Modeling gamma knife radiosurgical toxicity for multiple brain metastases

BACKGROUND AND PURPOSE

Radiation oncology protocols for single fraction radiosurgery recommend setting dosing criteria based on assumed risk of radionecrosis, which can be predicted by the 12 Gy normal brain volume (V12). In this study, we show that tumor surface area (SA) and a simple power-law model using only preplan variables can estimate and minimize radiosurgical toxicity.

MATERIALS AND METHODS

A 245-patient cohort with 1217 brain metastases treated with single or distributed Gamma Knife sessions was reviewed retrospectively. Univariate and multivariable linear regression models and power-law models determined which modeling parameters best predicted V12. The V12 power-law model, represented by a product of normalized Rx dose Rxn, and tumor longest axial dimension LAD (V12 ∼ Rxn1.5*LAD2), was independently validated using a secondary 63-patient cohort with 302 brain metastases.

RESULTS

Surface area was the best univariate linear predictor of V12 (adjR2 = 0.770), followed by longest axial dimension (adjR2 = 0.755) and volume (adjR2 = 0.745). The power-law model accounted for 90% variance in V12 for 1217 metastatic lesions (adjR2 = 0.906) and 245 patients (adjR2 = 0.896). The average difference ΔV12 between predicted and measured V12s was (0.28 ± 0.55) cm3 per lesion and (1.0 ± 1.2) cm3 per patient. The power-law predictive capability was validated using a secondary 63-patient dataset (adjR2 = 0.867) with 302 brain metastases (adjR2 = 0.825).

CONCLUSION

Surface area was the most accurate univariate predictor of V12 for metastatic lesions. We developed a preplan model for brain metastases that can help better estimate radionecrosis risk, determine prescription doses given a target V12, and provide safe dose escalation strategies without the use of any planning software.

Predictive Factors for Response to Adaptive Therapy in Thoracic Stereotactic Ablative Radiotherapy

PURPOSE/OBJECTIVE(S)

Online adaptive radiotherapy (ART) has been increasingly adopted for clinical use. However, ART for thoracic malignancies has lagged beyond its implementation for other primary cancers. Efforts are needed to identify optimal patients for ART by finding trends for changes in tumor position, shape, or proximity to OARs are needed. We hypothesized tumor size, histology, pre-RT SUV value, and intrathoracic location could influence how tumors change during cone beam computed tomography (CBCT)-based ART Stereotactic Ablative Radiotherapy (SAbR) for thoracic disease.

MATERIALS/METHODS

Data was collected from a prospective registry of patients who received CBCT-ART and SAbR for primary and secondary lung tumors. Dosimetry data was obtained from the simulation planning and the daily adaptive workflow. Central lung tumors were defined as those located within 2 cm of the bronchial tree. Plans were either delivered as per simulation or through the online adaptive workflow delivery (AD). Change in planning tumor volumes (PTV) were calculated between initial and final fractions (ΔPTV).

RESULTS

A total of 42 patients with a median age of 67 (range 17-90) and median 8.3 months follow up, treated between June 2021 and December 2022 were included. Most patients had NSCLC or presumed NSCLC (73.85%, 31/42), and most lesions were peripheral (61.9%, 26/42) versus central (31%, 13/42) or apical (7.1%, 3/42). Mean dose and median fractions were 52.5 Gy (SD 8.07) and 5 (range 3-5) while median initial (i) PTV was 31.75 cm3 (IQR 42.3 cm3). On average, ΔPTV decreased by 4.9% (SD 21) and volume shrunk by 5 cm3 (SD 14.5). AD improved per fraction PTV coverage and conformality while esophageal, cardiac, and spinal cord dose were significantly decreased (all p < 0.05), and most fractions were delivered with AD (73.4%, 138/188). AD was aborted most often for small iPTVs. ΔPTV grew >10% for two lesions though their iPTV were < 10 cm3. 12/42 ΔPTV were >10% smaller by the end of RT and corresponded to larger iPTVs. Age, lung primary, metastatic disease, smoking status, and tumor location were not predictive for >10% decrease in ΔPTV. Among 24 biopsy-proven NSCLC ΔPTV was >10% smaller in 6/12 patients (50%) with adenocarcinoma and only in 2/12 (16.7%) with SCC, although this was not significant on χ2 testing (p = 0.08). There were no differences in local, regional, distant failure or death comparing those with a ΔPTV of >10% vs <10% (all p > 0.1). Comparing pre-treatment PET SUV and tumor response, lower SUVs appear to be associated with more PTV shrinkage, with no significant PTV change plateauing at SUV 20. However, this analysis was limited by the number of patients with high SUV values.

CONCLUSION

CBCT-ART SAbR is associated with improved PTV coverage, target conformality, and reduced OAR dose. Large iPTV and adenocarcinomas were more likely to decrease >10%. High metabolic activity appeared predictive for a lack of significant ΔPTV. Further clinical and radiographic features should be explored to predict response to ART.

Cardiac Sparing with Volumetric Modulated Arc Therapy Enabled Total Body Irradiation (CS VMAT-TBI)

PURPOSE/OBJECTIVE(S)

Volumetric modulated arc therapy (VMAT) enabled total body irradiation (TBI) has replaced conventional TBI in our institution given the improved treatment accuracy, patient comfort, and dose modulation ability. The risk of cardiovascular disease is several folds higher among transplant patients who receive TBI, likely related to dose to the heart. We hypothesize that a cardiac-sparing (CS) VMAT-TBI technique is feasible and can meaningfully reduce dose to the heart while still adequately covering nearby lymphatic tissue.

MATERIALS/METHODS

VMAT-TBI is delivered via multi-isocentric external beams in a frame-based setup. Heart is contoured as per published guidelines. A lymph node contour, which includes tonsils, neck nodal stations, mediastinal, abdominal, retroperitoneal, and pelvic nodes is created. Coverage of the lymph node contour is prioritized over organ-sparing during inverse optimization; with a goal of V90% greater than 99.5% and mean dose less than 800 cGy for the lymph nodes and heart, respectively. An IRB-approved retrospective review was performed with mean heart dose collected for all patients treated with CS VMAT-TBI and compared to a representative cohort of five patients treated with VMAT-TBI without cardiac sparing.

RESULTS

Thirty-one patients were treated with CS VMAT-TBI between 2020-2022 with a median follow up time of 11.5 months. Mean heart dose was 796 ± 71 cGy in the CS VMAT-TBI compared to 1247 ± 29 cGy in the VMAT-TBI group without cardiac sparing (p < 0.001). Of those treated with CS VMAT-TBI, three patients relapsed; one relapse occurred in bone marrow only, one relapse occurred in bone marrow and cervical, thoracic, and intra-abdominal lymphoid tissues, and one patient was simulated but never received induction therapy due to overt progression. 100-day relapse-free survival and overall survival were 82.5% and 86.2%, respectively. Median survival time has not been met.

CONCLUSION

Cardiac sparing is feasible in VMAT-TBI and is associated with significant decrease in mean heart dose of ∼450 cGy. This is estimated to confer a 33.3% decreased absolute risk for lifetime major coronary events compared to patients treated with VMAT-TBI without cardiac sparing. Although limited by short follow-up time, there does not appear to be a significant risk for early relapse despite de-escalating cardiac tissue, likely due to prioritizing coverage of lymph nodes. Prospective clinical studies are needed to further validate cardiac and other organ at risk sparing VMAT-TBI techniques.

Towards Biology-Guided Radiotherapy Planning and Delivery on a Novel O-Ring PET-Linac Platform: Extended Beyond Bone and Lung Lesions

PURPOSE/OBJECTIVE(S)

Biology-guided radiotherapy (BgRT) with FDG signal collected via an on-board positron emission tomography (PET) system integrated in an O-ring gantry Linac was recently cleared by the FDA for lung and bone lesions. This study aims to determine if BgRT plans, guided via PET signal, are clinically acceptable for FDG-avid lesions in disease sites beyond bone and lung.

MATERIALS/METHODS

Ten patients previously treated for lesions in the liver, head and neck (HN), pancreas, renal and pelvic-abdominal lymph nodes were identified. Diagnostic PET/CT images of these treatment sites were first collected and processed/converted to mimic PET images that are acquired on PET-Linac and would be used to guide the delivery. For BgRT planning, the PTV was generated with 5 mm margin from GTV and a Biology Tracking Zone was generated including the anticipated full range of target motion. BgRT plans, guided by the emulated PET signal, were generated with 46Gy in 3 fractions for liver and 40Gy in 5 fractions for all other sites. BgRT plan deliverability was first assessed by evaluating the Activity Concentration (AC) and Normalized Target Signals (NTS) on converted PET images with the goal to meet NTS >2 (hard constraint) and AC >5kBq/ml (goal). BgRT plan quality was then evaluated with institutional guidelines on PTV coverage, OAR doses, conformity index (CI) and Heterogeneity index (HI).

RESULTS

BgRT plans were successfully generated for 11 target lesions among ten patients. The average diagnostic PET SUV, derived NTS and AC on converted PET images were 12.62, 9.33 and 12.10 kBq/ml, respectively. All images met the NTS constraints, and 8/11 plans met the AC goal for deliverability. All plans met the OAR hard constraints such as max dose on duodenum, small bowel, large bowel and spinal cord. Five of 11 plans had a limiting GI structure that resulted in an expected reduction in PTV coverage with an average PTV V100% = 77.9%, CI of 1.4, HI of 1.36 and max dose of 133.8%. The other 6 of 11 cases met the PTV V100% = 95%, had an average CI of 1.1, HI of 1.28 and Dmax of 127.67%. The estimated average time for BgRT delivery was 17 mins 25 secs. Although these plan parameters are deemed to be clinically acceptable, heterogeneity was detected inside the target region and suboptimal dose fall off was observed in some cases that may be caused by current implementation.

CONCLUSION

This preliminary study showed that BgRT plans were generated successfully with emulated PET images on 11 treatment sites covering HN, abdominal and pelvic regions. All plans met NTS constraints and 8 out of 11 met AC goals for deliverability. The plan quality of all BgRT plans were clinically acceptable based on institutional constraints. Further investigations are required to test more patients/sites for BgRT plan feasibility. Dosimetric benefit from margin reduction of BgRT target should also be investigated in future study.

Predicted Cardiac Toxicity in Daily Cone-Beam CT-Based Online Adaptive Stereotactic Partial Breast Irradiation with Decreased PTV Margins

PURPOSE/OBJECTIVE(S)

Partial breast irradiation (PBI) targets a smaller volume over less time compared to whole breast radiation, but the organ-at-risk (OAR) sparing allowed by its large (up to 1 cm) PTV can be improved. The heart is sensitive to low doses with conventional fractionation and NTCP models have been created for heart substructures. We hypothesized that daily online adaptive stereotactic PBI (A-SPBI) IMRT with 3-mm PTV improves dosimetry and predicted cardiac toxicity risk.

MATERIALS/METHODS

Patients treated with daily CBCT-based online A-SPBI IMRT were excluded if the minimum heart dose was <1 Gy. IMRT radiation plans with 3-mm PTV margins were recreated with 1-cm margins per the Florence APBI IMRT trial planning guideline. Dose statistics were converted to the equivalent doses in 2-Gy fractions (EQD2) using α/β = 3 for use in NTCP models and for comparison using paired t tests, with differences considered significant if p≤0.05.

RESULTS

The table details heart, left anterior descending artery (LAD), and left (LV) and right ventricle (RV) EQD2 statistics for 4 left-sided and 4 right-sided 3-mm PTV plans and their 1-cm PTV replans. For 2 patients with non-zero LV V5, 9-year excess cumulative risk of acute coronary event was <0.001% for both margin sizes. No plan reached thresholds for increased risk of non-cardiac death, major adverse cardiac event, or >10% decrease in LV ejection fraction.

CONCLUSION

Given the established relationship between low MHD and cardiac events, the significant decrease in MHD revealed in comparisons of 3-mm and 1-cm PTV A-SPBI plans of our first 8 patients is promising; we expect the forthcoming larger sample size to show significant differences in substructure doses. NTCP models created for non-IMRT breast plans and targets with higher heart exposure did not predict clinically-relevant differences in cardiac risk. NTCP model development for the low heart dose achieved with A-SPBI would define expected benefit in these patients; in their absence, daily adaptation should be considered in patients with unfavorable anatomy or cardiac risk factors.

Multi-Institutional Phase II Trial Using Dose Escalated Five Fraction Stereotactic Partial Breast Irradiation (S-PBI) with GammaPodTM for Early-Stage Breast Cancer

PURPOSE/OBJECTIVE(S)

We report on our early experience of a multi-institutional phase II study of dose escalated five fraction stereotactic partial breast irradiation (S-PBI) for early-stage breast cancer after partial mastectomy using the GammaPodTM stereotactic radiation system.

MATERIALS/METHODS

Patient eligibility included DCIS or invasive epithelial histologies, AJCC clinical stage 0, I, or II with tumor size < 3 cm, and negative margins. Prior safety of Phase I dose escalation has been reported. Dose was 40 Gy delivered in 5 fractions to the CTV, and minimum dose 30 Gy in 5 fractions to the PTV. CTV margin was 1 cm and PTV margin 3 mm. For PTV cavities larger than 100cc, dose was reduced to 35Gy in 5 fractions to the CTV and 30 Gy in 5 fractions to the PTV. Primary endpoint of the study is to determine the 3-year patient global cosmesis score (4-point scale excellent, good, fair, or poor) and adverse cosmesis using a dose escalated approach with smaller PTV margins than conventional methods. Both patients and physicians completed baseline and subsequent cosmesis outcome questionnaires. Treatment related toxicity was graded using the NCI version 4.0 and RTOG/EORTC late radiation scale.

RESULTS

From 3/2019-10/2021, 74 patients were treated respectively. Of these, 38 were treated to 40Gy and 36 were treated to 35 Gy. Median follow up (f/u) was 24 months (mo), range (r) 3-39mo. Median age was 63 years (r 43-77). Histology included 28 DCIS, and 46 invasive carcinomas. 45/46 invasive tumors were ER+. 60/74 (81%) patients received endocrine therapy, and 7/74 patient received chemotherapy. There were 221 acute grade 1 toxicities, and 28 Grade 2 toxicities. No grade 3 or higher acute toxicities were reported (< 90 days). The most common Grade 2 toxicities were radiation dermatitis (10), breast pain (8), blister (4), skin infection (2), nipple discharge (2), and fatigue (2). In the late period, there were 54 Grade 1 late toxicities, 4 Grade 2 late toxicities, and no Grade 3 or higher late toxicities. Grade 2 toxicities included fibrosis (2), and pain (2). Two patients developed grade 1 asymptomatic nonpalpable fat necrosis both diagnosed at 12 months after radiation treatments. The most common grade 1 late toxicities were breast pain (14), hyperpigmentation (8), fibrosis (10), and fatigue (5). Physicians scored cosmesis excellent or good 70/73 (95.8%), 58/60 (96.7%), 36/36 (100%),17/17(100%) respectively at baseline, 12 months, 24 months, and 36months post SBRT, while patients scored the same periods 62/71 (83.7%), 53/59 (89.8%), 33/36 (91.6%), 17/18 (94.4%). There have been no reports of disease recurrences.

CONCLUSION

Results at 24-month median follow-up, of our dose escalated stereotactic partial breast 5 fraction regimen, has low acute and late toxicity, while maintaining high proportion of excellent/good cosmetic outcomes. Continued analysis of all cohorts is in progress.

CLINICAL TRIALS

gov identifier is NCT03581136.

Assessment of Cardiac Radiation Dose in the Co-60 Prone Based Stereotactic Partial Breast Irradiation (CP-sPBI) Using the Distance from the Heart to the Planning Treatment Volume as a Surrogate Marker

PURPOSE/OBJECTIVE(S)

Irradiation of the breast has shown to provide sharp dose gradients using Co-60 prone based stereotactic partial breast irradiation (CP-sPBI), a contemporary device for stereotactic radiotherapy for breast cancer (BC) for accelerated partial breast irradiation (APBI). In addition, the precise setup of CP-sPBI permits a small planning treatment volume (PTV) margin of 3 mm creating a greater distance from PTV to organs at risk. However, to date the factors that influence dose gradients and subsequent cardiac doses of ionizing radiation using CP-sPBI have not been well-studied. Here we evaluate distance of the heart to the lumpectomy PTV cavity and how this effects cardiac dose.

MATERIALS/METHODS

A retrospective database of 113 consecutive patients treated by CP-sPBI for APBI from March 2019 to February 2023 who were treated with 30 Gy in 5 fractions were queried for analysis. The minimum distance from the heart to the PTV (hP) was measured in either the axial or sagittal view. A group of 28 patient cases were randomly selected to achieve an even distribution of 28 cases with hP < 2.75 cm and hP ≥ 2.75 cm to compare cardiac toxicities based on hP. Descriptive analyses were performed to evaluate various cardiac dosimetric parameters based on laterality of BC and hP, using the student's t test.

RESULTS

The mean (range) hP was 4.58 cm (0.80-12.23) for all cases. The subgroup analyses of 28 patient cases with cardiac parameters showed the heart mean (range) dose of 1.20 Gy (0.01-2.11). The mean and max heart dose to the left-sided BC were similar to those to the right-sided BC (mean dose: 1.20 vs. 1.19 Gy; P = 0.97 and max dose: 10.47 vs. 5.66 Gy; P = 0.06). An inverse correlation between hP and mean heart dose was shown with the correlation coefficient of -0.81. Using a cutoff of 2.75 cm hP, the differences between hP < 2.75 and hP ≥ 2.75 cm for all cardiac dosimetric evaluations were all statistically significant, including mean (1.67 vs. 0.79 Gy; p<0.01) and maximal heart dose (14.48 vs. 4.11 Gy; p<0.01) CONCLUSION: CP-sPBI treatment delivery system was able to achieve acceptable clinically relevant heart dosimetric parameters when delivering 5 fraction APBI with a mean heart dose of 1.20 Gy for all locations of PTV cavity volume in the breast. Due to CP-sPBIs excellent dose fall-off characteristics, APBI using CP-SPBI showed clinically acceptable cardiac dosimetric parameters, particularly for PTVs located > 2.75 cm from the heart.

Observed and Predicted Toxicity in Daily Cone-Beam CT-Based Online Adaptive Stereotactic Partial Breast Irradiation with Decreased PTV Margins

PURPOSE/OBJECTIVE(S)

Accelerated partial breast irradiation (APBI) delivers smaller radiation volumes over less time compared to whole breast irradiation (WBI), but the organ-at-risk (OAR) sparing allowed by its large (up to 1 cm) planning target volume (PTV) can be improved. PTV can be decreased with daily online adaptive planning, which we hypothesized yields low rates of adverse events observed and predicted by normal tissue complication probability (NTCP) models.

MATERIALS/METHODS

Intensity-modulated (IMRT) cone-beam CT (CBCT)-based daily online adaptive stereotactic PBI (A-SPBI) plans with 3-mm PTV from 8 patients were recreated with 1-cm PTV per the Florence APBI IMRT trial planning guideline. Dose statistics with evidence for association with toxicity were compared. Documented toxicities were collected for patients treated with A-SPBI with a minimum follow-up of 3.5 months and Common Terminology Criteria for Adverse Events (CTCAE) v.5.0 grade was assigned. Using α/β = 3 for breast and lung, dose statistics were converted to equivalent doses in 2-Gy fractions (EQD2) for use in NTCP models and for comparison using paired t tests, with differences considered significant if p≤0.05.

RESULTS

The table details EQD2 dose statistics for breast, lung, and cosmetic toxicity for A-SPBI plans with 3-mm PTV and their 1-cm PTV re-plans in 8 patients. PTV volume, mean lung dose (MLD), and lung V5, V20, and V30 were significantly lower in 1-cm plans. Acute, subacute (3-6 months), and late toxicities were collected for 30 patients followed for a median of 8 months (range 4-13 months). Radiation dermatitis was the most common acute toxicity (n = 16, 53%), followed by hyperpigmentation (n = 12, 40%), fibrosis (n = 9, 30%), and fatigue (n = 9, 30%). One grade 3 radiation dermatitis was the only grade ≥3 toxicity. Six patients (20%) acutely developed breast or axillary edema: 4 (13.3%) resolved, and 2 (6.7%) developed acutely and persist at last follow-up, >6 months after RT. No patient had a lung V20, V30, or MLD meeting thresholds for radiation-induced lung injury, radiation pneumonitis, or symptomatic or imaging-based pneumonitis models, respectively. The breast V55 model predicted a median risk of unfavorable cosmesis of 33% (range 26-44%) for A-SBPI plans and 35% (range 28-51) for 1-cm PTV plans (p = 0.28).

CONCLUSION

Observed acute toxicities are tolerable and rarely persist in patients treated with A-SPBI with 3-mm PTV margins with daily CBCT-based online adaptation. NTCP modeling predicts similar cosmetic outcome to 1-cm margins. The significant reduction in ipsilateral lung dose with a 3-mm PTV in our first 8 patients especially supports daily adaptation in low-risk breast cancer patients with smoking history and/or lung comorbidity.

Financial Toxicity and Patient Experience Outcomes on a Multi-Institutional Phase I Single Fraction Stereotactic Partial Breast Irradiation Protocol for Early-Stage Breast Cancer

PURPOSE/OBJECTIVE(S)

Given the demonstrated financial toxicity (FT) of radiation treatment on breast cancer patients shown in both conventional and our recent 5 fraction stereotactic APBI (S-PBI) study, we assessed the FT, as well as patient-reported utility, quality-of-life and patient experience measures, on patients treated in our phase I single fraction S-PBI trial.

MATERIALS/METHODS

A phase I single fraction dose escalation trial of S-PBI for early-stage breast cancer was conducted. Women with in-situ or stage I-II (AJCC 6) invasive breast cancer following breast conserving surgery were treated with S-PBI in 1 fraction to a total dose of 22.5, 26.5 or 30 Gy (Clinical trials.gov ID NCT02685332). At one month follow-up, patients were asked to complete our novel "Patient Perspective Cost and Convenience of Care Questionnaire". Patients also completed the EQ-5D-5L, including the visual analogue scale of overall health (VAS), at enrollment, 6, 12-, 24-, 36-, and 48-month follow-up.

RESULTS

Of 29 patients enrolled and treated, questionnaire data was available for all patients. Our trial encompassed a wide range of annual household incomes, education, and employment status. Overall, 44.8% (n = 13/29) of patients reported that radiation treatment presented a financial burden. Interestingly, no demographic information, such as patient race, marital status, education, household income, or employment during treatment predicted perceived FT. Patients reporting FT trended towards younger age (median 64 vs 70.5) and having a cancer related co-pay similar to our 5 fraction S-PBI FT trial; however, due to the small size of this study, this did not reach significance (p = 0.24 and 0.10, respectively). VAS and utility scores were calculated per the EQ-5D-5L and remained unchanged from baseline through 4-year follow-up. Likewise, there was no difference in the utility or VAS between patients who reported FT and those who did not. Interestingly, while patient reported cosmesis was similar for all patients at enrollment, patients who reported FT noted significantly worse cosmesis scores (fair/poor vs good/excellent) at 6 month and 2-year follow-ups (p = 0.01 and 0.04, respectively). Finally, patients were surveyed on treatment related disruption to their daily activities and enjoyment of life. The median values were 0 (scale 0-10, with 0 being no disruption) regardless of perceived FT. Patients were also uniformly satisfied with treatment time with a median score of 10 (scale 0-10, 10 being most satisfied).

CONCLUSION

Here, we show that despite using SPBI in a single fraction, nearly half of the patients treated still reported FT of treatment. Importantly, single fraction S-PBI has no negative impact on patient VAS or utility scores, and all patients were uniformly satisfied with treatment time without significant disruption to their life.

Could Poor Outcomes for Patients with Limited Lung Function Treated with SAbR Necessitate PULSAR?

PURPOSE/OBJECTIVE(S)

Stereotactic ablative radiotherapy (SAbR) employs precise targeting and delivery of ablative radiation doses in patients with medically inoperable early-stage non-small cell lung cancer, as well as patients with pulmonary metastases. SAbR is well tolerated with few studies reporting a minimal decline in pulmonary function tests (PFTs). However, poor pulmonary function is considered a risk factor for radiation induced lung toxicity. Personalized Ultrafractionated Stereotactic Adaptive Radiotherapy (PULSAR) is an adaptive radiation therapy regimen where radiation pulses are delivered over longer periods of time, thereby allowing for modification of the treatment based on the patient's response, as well as limiting toxicities. As such, we hypothesize that treating patients with poor pulmonary function using a PULSAR approach is better tolerated in when compared to patients treated with SAbR.

MATERIALS/METHODS

We performed a retrospective review of our institutional database of patients treated with SAbR to lung lesions from 2005 to 2022. We assessed the overall survival in stage-matched patients with normal vs poor lung function who received SAbR (40 patients in each cohort). Patients with decreased lung function included those with a diagnosis of moderate/severe COPD, restrictive lung disease, or patients needing home oxygen at the time of treatment. We then analyzed PFTs changes for patients receiving SAbR, and evaluated these changes relative to treatment delivery.

RESULTS

Stage-matched Kaplan-Meier analysis of patients with normal vs poor lung function receiving SAbR revealed a statistically significant difference in survival with Log-rank test p = 0.007. Of the patients with PFTs, 45 (90%) received SAbR with two to three treatments weekly, while 5 (10%) were treated on a PULSAR regimen with one fraction every week to three weeks. No trends or significant differences are observed in the changes of total lung capacity (TLC), the first second of exhalation (FEV1), forced vital capacity (FVC) or FEV1/FVC ratios. However, we did note variations in the diffusing capacity of the lung for carbon monoxide (DLCO). The mean difference in DLCO for the SAbR and PULSAR groups were -26.07% (95% CI: -31.28 to -20.87, p < 0.0001), and -10.52% (95% CI: -40.74 to 19.69, p = 0.388), respectively.

CONCLUSION

We observed a significant difference in overall survival between patients with normal vs poor lung function receiving SAbR. In a preliminary analysis, we discovered a small decline in DLCO for patients treated with regularly scheduled SAbR treatments. In the patients treated on the PULSAR regimen, however, this change in DLCO is not statistically significant. While this data suggests that increasing the time frame between individual doses of radiation may result in better toleration of radiotherapy in this patient population, the sample size of patients treated via PULSAR is limited, and longer follow-up is needed to further evaluate the potential benefits.

Predicting Neurocognitive Decline in Multiple Brain Metastases Patients Undergoing Distributed Stereotactic Radiosurgery

PURPOSE/OBJECTIVE(S)

Stereotactic radiosurgery (SRS) is the standard of care for treating a limited number (<3) of brain metastasis (BMs), which offers reduced neurotoxicity compared to whole brain radiotherapy (WBRT). Contemporary advancements in SRS made it possible to also commonly treat multiple (>4) BMs (mBMs). Emphasizing the value of preserving quality of life (QoL) after SRS, there is an urgent need for a systematic study of potential neurocognitive decline in patients receiving SRS treatment for mBMs. The purpose of this study is to use routine MRIs to predict neurocognitive decline for patients treated with distributed SRS, allowing for timely and effective treatment strategy design.

MATERIALS/METHODS

This study uses data from an institutional phase I/II clinical trial to determine the neurocognitive decline in patients with (>6) mBMs treated with distributed SRS. In the first 12 months post-SRS, participants are followed and evaluated with routine MRIs and the Hopkins Verbal Learning Test-Revised (HVLT-R) at 2 to 3-month intervals. Changes in HVLT-Delayed Recall scores between two visits are used to define neurocognitive decline. For each visit, an in-house deep learning model segments 66 cortical and 55 subcortical brain regions of interest (ROIs) from the T1 structural MRI and extracts 253 ROI features, including the surface area and thickness of cortical ROIs, and the volume of all ROIS. The difference in ROI features between two visits, together with other clinical factors (e.g., prescription, number of BMs, etc.), is considered as one sample. The study included 22 subjects with 91 visits, resulting in 171 samples with neurocognitive decline labels. The entire sample set is split into 10 folds on patient level for cross validation. In each fold, feature engineering is conducted to remove redundancy and to select the most-important features. The top 20% most frequently selected features are applied with Support Vector Machine to predict the neurocognitive decline label of each sample.

RESULTS

As a preliminary result, the proposed method achieves an accuracy of 76%, with an area under the curve (AUC) of 0.75, sensitivity of 0.65 and specificity of 0.83 for predicting neurocognitive decline in mBMs SRS patients using only routine T1 MRIs. The volume of lateral occipital complex, the thickness of inferior parietal lobe and postcentral gyrus, and the surface area of lateral orbitofrontal cortex and pars triangularis are identified as the 5 most important features for this task.

CONCLUSION

Our method shows promising findings for post-SRS neurocognitive decline prediction solely based on routine baseline and follow-up MRIs. In addition, it can identify critical brain ROIs associated with the post-SRS cognitive function. This method has the potential to assist treatment planning strategy to help preserve patients' QoL.

Stereotactic Ablative Radiotherapy for the Treatment of Glandular Metastases from Renal Cell Carcinoma

PURPOSE/OBJECTIVE(S)

Glandular metastases including pancreatic and adrenal sites of disease are associated with renal cell carcinoma (RCC) of indolent biology. Adrenal and pancreatic metastases may develop in isolation or involve other organs and are associated with prolonged survival. Glandular metastases can be treated with systemic therapy, stereotactic ablative radiotherapy (SAbR) or surgical resection and the optimal management of these patients is unknown. There is paucity of data on SAbR for RCC glandular metastases. We hypothesize that ablative doses of radiation therapy utilizing SAbR are associated with high rates of local control greater than 90%, with minimal or no acute grade 3 toxicities or higher with this approach. Here, we report local control (LC), progression-free survival (PFS), overall survival (OS) rates as well as toxicities related to SAbR for RCC metastases to the pancreatic and adrenal glands.

MATERIALS/METHODS

This IRB-approved, single-institution, retrospective study included patients with RCC metastases to the adrenal glands and pancreas treated with SAbR. Data on patient demographics, functional status, tumor characteristics, International Metastatic RCC Database Consortium (IMDC) risk category, local and systemic treatments, toxicities, and outcomes were collected and analyzed. RECIST 1.1 principals were utilized to determine LC rates and PFS. PFS was determined from the initiation of SAbR to progression (at SAbR-treated or other sites), or death. OS was defined from the start of SAbR to death. Two independent reviewers assessed these measures and analyzed patient electronic health records for toxicities using CTCAE v5 and relatedness scores.

RESULTS

A total of 50 RCC patients were included in this study with 36 adrenal and 20 pancreatic metastases treated with SAbR. Median dose fractionation used was 40 Gray delivered in 5 fractions. Sixteen patients (32%) were treatment naïve with oligometastatic disease, and thirty-four (68%) were oligo-progressive on systemic therapy with 1-3 prior lines of systemic therapy. For treated adrenal metastatic lesions at 1 year, patients demonstrated a 75.3% OS, 46.7% PFS, and LC of 93.3%. For treated pancreatic metastatic lesions at 1 year, patients demonstrated a 100% OS, 48.6% PFS, and LC of 100%. At 1 year, there was an OS of 82.2%, PFS of 48.2%, and LC of 95.9 % in the combined cohort. The percentage of patients experiencing an acute grade 2 or 3 toxicity attributed to adrenal or pancreatic gland SAbR was 7.4%. There were no acute grade >3 toxicities. The percentage of patients experiencing a late grade 2 or 3 toxicity was 9.3%. Median time to late adverse events was 37.4 months.

CONCLUSION

SAbR of RCC metastases to the pancreas and adrenal glands is feasible, safe and appears to be effective. Median PFS and OS in this cohort compared favorably to those reported in historical cohorts and is consistent with indolent disease.

Analysis of the Measured FDG Uptake from the First-in-Human Clinical Trial of Biology-Guided Radiotherapy

PURPOSE/OBJECTIVE(S)

The RefleXion X1 system is a novel linear accelerator equipped with dual 90° PET arcs incorporated into its architecture to capture emissions from tumors and designed to respond by directing the radiation beam towards target. This study reports on the measured FDG uptake from the first in human multi-institutional clinical trial (BIOGUIDE-X) evaluating the performance and safety of the RefleXion X1 PET-LINAC.

MATERIALS/METHODS

A total of nine patients treated with stereotactic body radiotherapy (SBRT) for lung (5) and bone (4) tumors were enrolled in the Cohort II of this study after screening their pre-study diagnostic PET/CT, acquired up to 60 days prior to enrollment, to ensure their tumor size between 2 to 5 cm and SUVmax >6. After CT simulation, the tumor and OARs were delineated, and patients had a 4-pass Imaging-only (BgRT Modeling) PET/CT acquisition on the X1 system to generate biology-guided radiotherapy (BgRT) plans. Before the patients' first and last SBRT fractions, they were injected with FDG, and short PET pre-scan (1-pass) was performed on the X1 followed by a long-PET acquisition (4-pass) to emulate the expected BgRT dose distribution without firing beam. Patients were also imaged on a third-party diagnostic PET/CT scanner after the last-fraction X1 scan. This study compares the SUVmax from the screening PET/CT, X1 Imaging-only scan, X1 PET pre-scan and long scan before the first and last-fractions, and final diagnostic PET/CT.

RESULTS

The median time from injection to PET imaging was 84 ± 15.4 mins for X1 Imaging-only (used for generating BgRT plans), 77 ± 21.6 mins for X1 pre-scan (safety check before treatment start), 108+/- 22 mins for X1 long-PET (used to emulate treatment delivery), and 161 ± 23 mins for final diagnostic PET. For a nominal 10 mCi injection, the mean SUVmax for screening imaging performed on the diagnostic PET/CT was 10.8 ± 4.3. For a 15 mCi nominal injection, the mean SUVmax calculated on the X1 was 5.3 ± 2.6, 5.4 ± 2.0, 5.5 ± 2.6, 5.2 ± 1.8 and 5.4 ± 2.2 for the Imaging-only, first-fraction PET pre-scan, first-fraction long PET scan, last-fraction PET pre-scan, and last-fraction long PET scan, respectively. The overall median SUVmax for all patients across all timepoints and scans with X1 was calculated to be 4.8 with a range of 2.4 to 9.8. The median SUVmax for the diagnostic PET/CT scan after the last fraction X1 scan was 15.8 with a range of 8.5 to 27.7.

CONCLUSION

The dual PET arcs and limited axial extent of the X1 PET subsystem results in lower system sensitivity in comparison to diagnostic PET scanners equipped with full ring and larger axial extent, as expected. With the same FDG injection, the RefleXion X1 produced SUVmax values that were 30.4 % of the diagnostic PET/CT scanners' values. Nevertheless, the X1 collected sufficient emission data to enable successful completion of emulated BgRT deliveries that met dose accuracy criteria in a clinical setting.

Imaging Performance of the PET Scan on a Novel Ring Gantry-Based PET/CT Linear Accelerator System in the First-in-Human Study of Biology-Guided Radiotherapy

PURPOSE/OBJECTIVE(S)

Biology-guided radiotherapy (BgRT) is a novel tracked dose delivery modality using real-time positron emission tomography (PET) to guide radiotherapy beamlets. The present study was performed with sequential cohorts of participants to evaluate the performance and safety of BgRT. Primary endpoints were previously reported. We hereby report on one of the secondary endpoints assessing a novel treatment planning machine with integrated dual kVCT/PET imaging ("novel device") performance in comparison to a third-party diagnostic PET/CT scan.

MATERIALS/METHODS

This single-arm, open-label, prospective study included participants with at least 1 FDG-avid targetable primary or metastatic tumor (≥2cm and ≤5cm) in the lung or bone. PET imaging data were collected on the novel device and on a third-party diagnostic PET/CT performed in sequence once at the planning timepoint in Cohort I, and immediately before the last fraction among patients undergoing stereotactic radiotherapy in Cohort II. Three central read radiation oncologists (CRRO) provided an interpretation of the novel device PET scans which were compared to an agreement standard based on 3 central radiologists' review of the paired diagnostic PET/CT scan. Positive percent agreement for localization of the target tumor within the biology-tracking zone (BTZ) was the key metric because it reflects whether advancing patients to subsequent steps in the BgRT workflow based on the novel device's imaging was ultimately appropriate.

RESULTS

In Cohort 1, 6 image comparisons were performed. The positive (%) agreement for the aggregate radiation oncologist review was 100% (5/5), reflecting that in all 5 cases where the aggregate radiation oncologists deemed the tumor to fall within the BTZ based upon the novel device PET images, the central radiologists came to the same conclusion upon review of the paired diagnostic PET/CT images. The overall (%) agreement for the aggregate radiation oncologist review was 83.3% (5/6): localization was not established on the novel device in 1 case, even though it was established on the diagnostic PET/CT. This would not pose risk in real world practice as BgRT candidacy would be aborted for tumors not visible on the novel device. In Cohort II, among the 7 image comparisons, there was 100% positive percent agreement between the aggregate CRRO and the agreement standard as the localization criteria was met in both scans for all 7 patients. This was concordant with a 100% overall percent agreement.

CONCLUSION

This investigation demonstrated a 100% positive percent agreement between central review of this novel device images by radiation oncologists and central review of the accompanying third-party PET/CT images by radiologists. There were no cases where a positive localization by the aggregate CRRO was not confirmed by the third-party PET/CT standard, providing evidence against the likelihood of falsely positive localizations on the novel device that would inappropriately advance patients in the workflow.

Dosimetric Comparison of Adaptive Radiotherapy Modalities for Stereotactic Partial Breast Irradiation

PURPOSE/OBJECTIVE(S)

An increase in the availability of adaptive radiotherapy (ART) platforms have proven to be effective in the treatment of a variety of sites. In this study, we aim to evaluate the effectiveness of non-adaptive RT and 3 different ART platforms: (1) CBCT-based, (2) CT-based, and (3) MRI-based for stereotactic partial breast irradiation (SPBI).

MATERIALS/METHODS

Data were collected from 32 patients (16 left and 16 right breast) treated at a single institution. 16 patients (8 left and 8 right) treated using the non-ART platform were re-planned onto two different ART platforms, CBCT- and MRI-based. The remaining 16 patients treated using CT-based adaptive platform were not re-planned due to the prone patient treatment position (others systems supine). All cases were planned to 30 Gy in 5 fractions. Plan quality was evaluated based on pre-defined planning goals to the OARS: ipsilateral and contralateral lungs (Dmean, Dmax, V20 Gy, V9 Gy), ipsilateral (V15 Gy, V30 Gy) and contralateral breasts (Dmax), heart (Dmean, Dmax, V3 Gy, V1.5 Gy), skin (Dmax, V36.5 Gy), and rib (Dmax, V30 Gy). Target goals were defined by Dmax, Dmin, gradient index, and paddock conformality index. Re-planned cases were compared within the cohort using a paired t-test and a 2-sided t-test was used comparing to the CT-based platform.

RESULTS

Comparing the left and right breast cohort across all platforms, the CT-based ART system showed a signification dose reduction in Dmean (p<0.001 for all platforms), Dmax (p<0.001 for left breast, p<0.03 for right breast) and V9 Gy (p<0.004 for left breast, p<0.001 for right breast) to the ipsilateral lung, V15 Gy (p<0.004 for left breast cohort) to the ipsilateral breast, and Dmax to the contralateral breast (p<0.001) and ribs (p = 0.01, p<0.001, p = 0.01 for CBCT-ART, MRI-ART, and non-ART for left breast cohort only). On average, the MR-Linac platform showed the least degree of OAR sparing across nearly all dosimetric parameters evaluated when compared to all modalities, especially for contralateral lung Dmean and Dmax (p<0.05 for all dosimetric parameters for all platforms) and contralateral breast Dmax (p<0.003 for all platforms). The CBCT-based platform showed superior dose reduction in contralateral lung mean (p<0.03 for all platforms) and heart Dmean (p = 0.065, p<0.001, p = 0.045 for non-adaptive, MRI-ART, and CT-ART for left breast and p<0.008 for right breast). PTV coverage was comparable across all platforms, averaging at approximately 95%. The CT-based ART platform showed a significantly reduced gradient index relative to the CBCT- and MRI-based platforms (p<0.001).

CONCLUSION

For SPBI treatments, the CT-based ART platforms displayed a higher degree of OAR sparing for many of the dosimetric parameters recorded relative to the other ART and non-ART platforms presented. The MRI-based system typically showed less reduced OAR sparing; however, the advantage of the system is shown if soft tissue contrast is needed. PTV coverage remained comparable across all platforms.

Workflow Considerations for Biology-Guided Radiotherapy (BgRT) Implementation

PURPOSE/OBJECTIVE(S)

Biology-guided radiotherapy (BgRT) is a novel platform that combines real-time PET imaging with a 6MV Linac to target tumors. The performance and safety of BgRT was assessed in the BIOGUIDE-X clinical trial. This study aims to report on the BgRT workflow steps and assess the time required for each step of the BgRT process during this trial.

MATERIALS/METHODS

A total of nine patients were enrolled in the second Cohort of the BIOGUIDE-X study which included patients treated with stereotactic body radiotherapy (SBRT) for lung tumors (5) and bone tumors (4). The pre-treatment BgRT workflow includes CT simulation, contouring, imaging-only (BgRT Modeling) PET acquisition, BgRT planning, patient specific QA and plan approval. The imaging-only PET acquisition on the X1 collects a representative PET volumetric 3D image and is an input to develop the BgRT treatment plan. The steps during the BgRT delivery session are kVCT localization, PET pre-scan, PET evaluation and BgRT delivery. The PET PreScan is a 1-pass short-duration PET acquisition that is used to confirm that the PET biodistribution on the day of treatment is consistent with that of the imaging-only PET. During BIOGUIDE-X, the BgRT delivery step was replaced by a 4-pass long-PET acquisition that was used to emulate the expected BgRT dose distribution without turning the beam on. To assess BgRT workflow, times from 18F-FDG injection to image-only PET acquisition, 18F-FDG injection to PET pre-scan, Pre-scan to PET evaluation, and PET evaluation to BgRT delivery (long PET acquisition) were recorded.

RESULTS

Time between the 18F-FDG injection and the X1 imaging-only PET scan was 84 ± 19 minutes which includes time for 18F-FDG update. Average time to perform imaging-only PET scan was 26 ± 4 minutes. During the BgRT 'delivery' session, the mean time between the kVCT acquisition and PET pre-scan acquisition was 7 ± 3 minutes. The mean time to acquire a 1-pass PET pre-scan was 6 ± 1 then followed by 6 ± 1 minutes for the PET pre-scan dose calculation to estimate the BgRT doses that it would have delivered for this fraction. On average, the PET reconstruction, the PET signal localization verification and the evaluation of safety metrics took 11 ± 4 minutes. The mean time for BgRT 'delivery' was 27 ± 5 minutes based on the 4-pass long PET acquisition. Time from the start of the BgRT session to the end of the BgRT 'delivery' with this version of the investigative product release was 65 ± 9 minutes.

CONCLUSION

The new processes introduced by the BgRT technology were evaluated and found clinically feasible. Improvements are being undertaken to shorten the time required for each step and to increase patient comfort ahead of BgRT clinical implementation.

Tracking Changes in Global Longitudinal Strain in Lung Cancer Patients Receiving Thoracic Radiation

PURPOSE/OBJECTIVE(S)

Thoracic radiation improves survival in many lung cancer patients. However, radiation-induced cardiotoxicity is a major source of morbidity and mortality in such patients. Global longitudinal strain (GLS), a novel echocardiography (ECHO) method of assessing left ventricular function, has been shown to predict long-term adverse cardiovascular risk in diverse patient populations. We hypothesized that receipt of thoracic radiation is associated with GLS changes in lung cancer patients.

MATERIALS/METHODS

We retrospectively identified patients with lung cancer treated at our institution between 2005-2020 who had ECHOs performed both before and after RT, and in whom GLS was extractable. ECHO Board-Certified cardio-oncologists measured GLS and left ventricular ejection fraction (LVEF) from these ECHOs.

RESULTS

A total of 40 patients met inclusion criteria. Median time to ECHO was 78 days prior and 172 days after RT. Two chamber (2C), 3C, 4C, and average GLS were significantly decreased after RT on paired t-test [mean difference (SD) 2.23 (3.29), 2.99 (2.78), 2.25 (3.63), 2.51 (2.66) respectively, all p < 0.001]. Thirteen patients (32.5%) had abnormal GLS (<18%) prior to RT. 5 of those 13 patients (38.5%) had abnormal LVEF (< 50%). 27/40 patients (67.5%) had an abnormal GLS or clinically significant (≥15%) drop in GLS after RT. This difference (32.5% patients pre-RT vs 67.5% post-RT) was statistically significant (p < 0.01). Among patients (n = 27) who had normal LVEF before RT, 1 patient (3.7%) developed abnormal LVEF (<50%) after RT. Backwards logistic regression showed significant interaction between heart volume receiving 5 Gray and change in GLS.

CONCLUSION

This cohort exhibited a significant decrease in 2C, 3C, 4C, and average GLS after RT. ∼1/3 of patients had abnormal GLS at baseline (suggesting a high-risk group for cardiac complications) and 67.5% of patients had clinically significant decrease in GLS after RT. Among the patients with normal GLS before RT, although 51.9% of patients demonstrated a clinically significant drop in GLS after RT, only 3.7% of patients developed abnormal LVEF, suggesting that this is a late occurrence. GLS changes may serve as a valuable tool for early identification of patients who are at high risk for future cardiac complications after receiving thoracic radiation.

Phase I Trial of 'Re-Priming' Radiation Therapy for Relapsed/Refractory Non-Hodgkin Lymphoma Patients in Incomplete Response after Chimeric Antigen Receptor T-Cell (CAR-T) Therapy

PURPOSE/OBJECTIVE(S)

Inpatients with relapsed/refractory non-Hodgkin lymphoma (R/R NHL) treated with CD19-directed CAR-T, only ∼40% achieve complete response (CR) by day 30 PET/CT evaluation. Of those who do not, the large majority (∼70%) ultimately fail, providing an ideal target for early therapeutic intervention to 're-prime' CAR-T. Preclinical and early clinical studies suggest potential synergy and immune augmentation when combining RT with CAR-T. Here we report the phase I results of a prospective phase I/II clinical trial hypothesizing that early salvage focal RT to poor responding sites of disease after CAR-T in R/R NHL patients is safe (phase I) and will improve conversion to CR by day 90 post-CAR-T PET/CT from 29% (historical control) to 58% (phase II).

MATERIALS/METHODS

Weopened a single-arm open-label phase I/II prospective clinical trial at our institution for R/R NHL patients treated with CD19-directed CAR-T with incomplete response on day 30 post-CAR-T PET/CT scan (defined as Lugano > = 4). The phase I component used a 'Rolling 6' design with 6 patients enrolled concurrently at the "definitive" dose level (40-50 Gy EQD2 [i.e., 30 Gy in 5 fractions], with de-escalation to "palliative" dose level (20-32.5 Gy EQD2 [i.e., 20 Gy in 5 fractions]) if >2 dose-limiting toxicities (DLT) observed. Hypofractionated regimens (i.e., 5 fractions) directed only to residual FDG-avid disease were recommended to minimize lymphopenia and potentially result in a more favorable immune microenvironment. DLT rate was defined within 60 days of RT by CTCAE v5.0 grade 4+ hematologic, grade 3+ dermatitis/burn, pneumonitis, enteritis, or other toxicity attributable to RT, as well as new grade 3+ cytokine release syndrome (CRS) per ASTCT consensus guidelines or grade 3+ neurotoxicity per ASTCT ICANS consensus guidelines for adults.

RESULTS

BetweenApril 2021 and July 2022, 6 patients were enrolled. All 6 patients had diffuse large B-cell lymphoma (DLBCL), with 3/6 (50%) transformed from low-grade follicular lymphoma. 2/6 had primary refractory DLBL, while the other 4/6 had median 2.5 lines of treatment prior to CAR-T. No patient had prior RT to a site of residual FDG-avid disease on day 30 post-CAR-T PET/CT. 5/6 patients were treated to 30 Gy in 5 fractions, with the remainder patient treated to 36 Gy in 10 fractions. No grade 3+ DLTs related to RT were observed in the 60-day post-RT period. RT related toxicities included grad 1 alopecia, grade 1 radiation pneumonitis, grade 1 nausea & vomiting, and grade 2 skin infection.

CONCLUSION

Early salvage focal "definitive" dose RT to sites of incomplete response on day 30 post-CAR-T PET/CT for R/R/ NHL patients was safe with no de-escalation of dose needed. This dose will used in the subsequent phase II component of the trial.

Post-Progression Survival in Patients with Oligometastatic or Polymetastatic Pancreatic Adenocarcinoma

PURPOSE/OBJECTIVE(S)

Distant progression following surgical resection of stage I-III pancreatic ducal adenocarcinoma (PDAC) is a major cause of morbidity and mortality. Herein, we investigated the impact of tumor burden at the time of distant progression on survival. We hypothesize that patients with limited number of metastases (≤5) in a single organ will have improved survival post progression.

MATERIALS/METHODS

We queried our institutional database for patients with the following inclusion criteria: 1-Stage I-III PDAC who underwent curative resection, and 2-Metachronous single organ (liver or lung) distant failure >3 months from the date of surgery. Patients with serosal and/or multiple organ metastases were excluded. Single organ metastases other than liver or lung were also excluded. Patients were stratified into oligometastatic (≤5 tumors), and polymetastatic (>5 tumors). Primary endpoint was survival post failure, while secondary endpoints were distant failure free survival (DFFS) and overall survival. Reverse KM curve was used to calculate median follow up. KM curves were plotted for DFFS identified from date of surgery until date of distant failure, survival post failure was identified from date of distant failure until death/last follow up, and overall survival was identified from date of surgical resection until death/last follow up.

RESULTS

Out of 128 patients who developed metachronous distant progression following surgical resection, we identified 76 patients who met the inclusion criteria with a median follow up of 50 months. Among those, at the time of distant failure, 63% (n = 48) and 37% (n = 28) patients had ≤5 vs >5 metastases respectively. Median number of metastases was one (range 1-5) and eight (range 6-33), while 12 and 11 patients developed local failure in the oligometastatic and polymetastatic cohorts respectively. Among the 48 patients who developed oligometastases, 69% (n = 33) and 31% (n = 15) had liver and lung metastases respectively. On the other hand, 68% (n = 19) and 32% (n = 9) had liver and lung polymetastases respectively. Median DFFS was 11, and 9 months (HR = 1.59, 95 % CI 0.95-2.64, p value = 0.046), survival post distant failure was 17.8 and 5.3 months (HR = 3.03, 95 % CI 1.52-6.01, p value<0.0001), and median survival was 29.8, and 16.7 months (HR = 2.52, 95 % CI 1.31-4.86, p value = 0.0007) among patients with oligometastases and polymetastases respectively.

CONCLUSION

Within the surgically resected stage I-III PDAC who developed single organ liver or lung metachronous disease, oligometastases (one-five lesions) were more prevalent, had more durable DFFS, had improved survival post failure, and a longer median survival compared to patients with polymetastatic recurrence (>five metastases). Trials on treatment of metastatic PDAC should stratify by number of metastases, and the oligometastatic subset may derive survival benefit from ablative radiation therapy.

The Changing Profile of Academic Radiation Oncology Leaders: Updates over the Past Decade

PURPOSE/OBJECTIVE(S)

To report objective characteristics of program directors (PDs) and chairpersons and examine contemporary trends of their demographic and academic profiles from 2013 to 2023. We hypothesize that there are significant changes in the profiles of our radiation oncology leaders over the past decade.

MATERIALS/METHODS

A total of 89 PDs and 85 chairpersons in the Accreditation Council for Graduate Medical Education (ACGME)-approved residency programs in the U.S were queried for analysis. Demographic data on race, ethnicity, post graduate training, years in practice were obtained from publicly available online resources (e.g., institutional websites and online networking services for physicians). Variables on academic productivity and professional accolades included Hirsh-index, National Institute of Health (NIH) research grant (R), the ASTRO fellowship designation, and leadership positions in professional society meetings. Descriptive analyses, including Fisher's exact tests, were performed to compare findings from the published article in 2013 on this topic (Wilson LD et al. IJROBP 2013).

RESULTS

A total of 36 out of 89 PDs (40.4%) and 11 out of 85 chairpersons (12.8%) were females, revealing higher proportion of females from the initial analysis: 40.4 vs. 24.1% for PDs (p = 0.025) and 12.8 vs. 9.2% for chairpersons (p = 0.618). 29 out of 89 (32.6%) PDs and 30 out of 85 (35.3%) chairpersons were non-White. The median length of practice for PDs and chairpersons were 11 and 29 years, respectively. 38 out of 89 PDs (42.7%) and 11 out of 85 (12.9%) chairpersons were employed at the institution of their training. 7 out of 89 (7.9%) for PDs and 51 out of 85 (60.0%) for chairpersons were awarded FASTRO designation. Median H-index showed increasing trends for PDs (14.5 vs 9) and chairpersons (40 vs 29) from the initial analysis.

CONCLUSION

While most PDs and chairpersons are males, female representation has increased in radiation oncology leadership in the last 10 years, most notably among PDs. Academic productivity among our leaders has also increased. These trends highlight the changes in the landscape of our leadership characteristics.

Consensus Quality Measures and Dose Constraints for Lung Cancer From the Veterans Affairs Radiation Oncology Quality Surveillance Program and ASTRO Expert Panel

PURPOSE

For patients with lung cancer, it is critical to provide evidence-based radiation therapy to ensure high-quality care. The US Department of Veterans Affairs (VA) National Radiation Oncology Program partnered with the American Society for Radiation Oncology (ASTRO) as part of the VA Radiation Oncology Quality Surveillance to develop lung cancer quality metrics and assess quality of care as a pilot program in 2016. This article presents recently updated consensus quality measures and dose-volume histogram (DVH) constraints.

METHODS AND MATERIALS

A series of measures and performance standards were reviewed and developed by a Blue-Ribbon Panel of lung cancer experts in conjunction with ASTRO in 2022. As part of this initiative, quality, surveillance, and aspirational metrics were developed for (1) initial consultation and workup; (2) simulation, treatment planning, and treatment delivery; and (3) follow-up. The DVH metrics for target and organ-at-risk treatment planning dose constraints were also reviewed and defined.

RESULTS

Altogether, a total of 19 lung cancer quality metrics were developed. There were 121 DVH constraints developed for various fractionation regimens, including ultrahypofractionated (1, 3, 4, or 5 fractions), hypofractionated (10 and 15 fractionations), and conventional fractionation (30-35 fractions).

CONCLUSIONS

The devised measures will be implemented for quality surveillance for veterans both inside and outside of the VA system and will provide a resource for lung cancer-specific quality metrics. The recommended DVH constraints serve as a unique, comprehensive resource for evidence- and expert consensus-based constraints across multiple fractionation schemas.

Stereotactic Radiosurgery vs Conventional Radiotherapy for Localized Vertebral Metastases of the Spine: Phase 3 Results of NRG Oncology/RTOG 0631 Randomized Clinical Trial

Importance

Spine metastasis can be treated with high-dose radiation therapy with advanced delivery technology for long-term tumor and pain control.

Objective

To assess whether patient-reported pain relief was improved with stereotactic radiosurgery (SRS) as compared with conventional external beam radiotherapy (cEBRT) for patients with 1 to 3 sites of vertebral metastases.

Design, Setting, and Participants

In this randomized clinical trial, patients with 1 to 3 vertebral metastases were randomized 2:1 to the SRS or cEBRT groups. This NRG 0631 phase 3 study was performed as multi-institutional enrollment within NRG Oncology. Eligibility criteria included the following: (1) solitary vertebral metastasis, (2) 2 contiguous vertebral levels involved, or (3) maximum of 3 separate sites. Each site may involve up to 2 contiguous vertebral bodies. A total of 353 patients enrolled in the trial, and 339 patients were analyzed. This analysis includes data extracted on March 9, 2020.

Interventions

Patients randomized to the SRS group were treated with a single dose of 16 or 18 Gy (to convert to rad, multiply by 100) given to the involved vertebral level(s) only, not including any additional spine levels. Patients assigned to cEBRT were treated with 8 Gy given to the involved vertebra plus 1 additional vertebra above and below.

Main Outcomes and Measures

The primary end point was patient-reported pain response defined as at least a 3-point improvement on the Numerical Rating Pain Scale (NRPS) without worsening in pain at the secondary site(s) or the use of pain medication. Secondary end points included treatment-related toxic effects, quality of life, and long-term effects on vertebral bone and spinal cord.

Results

A total of 339 patients (mean [SD] age of SRS group vs cEBRT group, respectively, 61.9 [13.1] years vs 63.7 [11.9] years; 114 [54.5%] male in SRS group vs 70 [53.8%] male in cEBRT group) were analyzed. The baseline mean (SD) pain score at the index vertebra was 6.06 (2.61) in the SRS group and 5.88 (2.41) in the cEBRT group. The primary end point of pain response at 3 months favored cEBRT (41.3% for SRS vs 60.5% for cEBRT; difference, -19 percentage points; 95% CI, -32.9 to -5.5; 1-sided P = .99; 2-sided P = .01). Zubrod score (a measure of performance status ranging from 0 to 4, with 0 being fully functional and asymptomatic, and 4 being bedridden) was the significant factor influencing pain response. There were no differences in the proportion of acute or late adverse effects. Vertebral compression fracture at 24 months was 19.5% with SRS and 21.6% with cEBRT (P = .59). There were no spinal cord complications reported at 24 months.

Conclusions and Relevance

In this randomized clinical trial, superiority of SRS for the primary end point of patient-reported pain response at 3 months was not found, and there were no spinal cord complications at 2 years after SRS. This finding may inform further investigation of using spine radiosurgery in the setting of oligometastases, where durability of cancer control is essential.

Trial Registration

ClinicalTrials.gov Identifier: NCT00922974.

Tissue assessment of therapeutic responses to neoadjuvant short course radiotherapy with and without anti-CD40 immunotherapy sotigalimab (sotiga) in rectal cancer

191

Background: There has been tremendous progress in the management of rectal cancer in the neoadjuvant setting and in non-operative management (NOM). However, there is a critical need to personalize systemic therapy and radiotherapy to achieve responses conducive for NOM. This study was initiated to profile immune changes to therapy in serial tumor tissue, blood, and stool from the INNATE trial (NCT04130854). Methods: INNATE, is a multi-institutional Phase II randomized trial for patients with Stage III or high-risk Stage II rectal cancer. Patients were randomized 3:2 to receive daily short course radiotherapy (SCRT- 5 Gy x 5) and 6 cycles of FOLFOX +/- 6 infusions of sotiga, an anti-CD40 agonist, followed by surgery. The primary end point is the pathologic complete response rate and additional clinical endpoints are being assessed. Biopsies of tumor and adjacent tissue before and 2 weeks after SCRT +/- sotiga prior to chemotherapy were obtained from consenting patients. Fresh tissue was digested into single cell suspension for scRNAseq with proteomic and immune repertoire analysis. Fixed tissue was processed for histology and multiplexed immunofluorescence. Here, we report integrated and batch effect removed data from 9 patients pre- and post-therapy and analyzed patients as their own control. Results: A total of 25 of 30 patients were enrolled at UTSW, 21 of whom underwent pre- and post-SCRT biopsies. The study population was diverse: 11 patients (37%) were Hispanic and 15 (50%) uninsured receiving care at the Dallas County hospital, Parkland. The median age was 55 (27-75) years and 13 (43.3%) were diagnosed prior to age 50. From integrated scRNAseq, we observed a significant induction of genes associated with M1- and M2-like macrophages, and dendritic cell antigen presentation in the SCRT alone group. This was accompanied by a robust Th1 and B cell response, but not T cell mediated cytotoxicity. In the SCRT + sotiga group there was a greater induction of genes associated with M1-like macrophages and dendritic cell antigen presentation, with no change in M2 genes. In lymphocytes, sotiga treatment led to an induction of genes related to Th1 and B cell response. Unlike SCRT, the combination therapy group had evidence of induced T cell mediated cytotoxicity. To better understand individual responses to therapy, we analyzed pre- and post-treatment samples for each patient. This enabled identification of features associated with poor and robust response in each treatment group. Conclusions: On treatment biopsies during neoadjuvant therapy for rectal cancer enables deep assessment of therapeutic response, provides insight into action of investigational agents, and may identify therapy specific predictive biomarkers. Our data shows that SCRT can induce immune responses and adaptive immune responses can be further induced by sotiga.

Impact of CDKN2A/B, MTAP, and TERT Genetic Alterations on Survival in IDH Wild Type Glioblastomas

PURPOSE

Poor outcomes in IDH wild-type (IDHwt) glioblastomas indicate the need to determine which genetic alterations can indicate poor survival and guidance of patient specific treatment options. We sought to identify the genetic alterations in these patients that predict for survival when adjusting particularly for treatments and other genetic alterations.

METHODS

A cohort of 167 patients with pathologically confirmed IDHwt glioblastomas treated at our institution was retrospectively reviewed. Next generation sequencing was performed for each patient to determine tumor genetic alterations. Multivariable cox proportional hazards analysis for overall survival (OS) was performed to control for patient variables.

RESULTS

CDKN2A, CDKN2B, and MTAP deletion predict for worse OS independently of other genetic alterations and patient characteristics (hazard ratio [HR] 2.192, p = 0.0017). Patients with CDKN2A copy loss (HR 2.963, p = 0.0037) or TERT mutated (HR 2.815, p = 0.0008) glioblastomas exhibited significant associations between radiation dose and OS, while CDKN2A and TERT wild type patients did not. CDKN2A deleted patients with NF1 mutations had worse OS (HR 1.990, p = 0.0540), while CDKN2A wild type patients had improved OS (HR 0.229, p = 0.0723). Patients with TERT mutated glioblastomas who were treated with radiation doses < 45 Gy (HR 3.019, p = 0.0010) but not those treated with ≥ 45 Gy exhibited worse OS compared to those without TERT mutations.

CONCLUSION

In IDHwt glioblastomas, CDKN2A, CDKN2B, and MTAP predict for poor prognosis. TERT and CDKN2A mutations are associated with worse survival only when treated with lower radiation doses, thus potentially providing a genetic marker that can inform clinicians on proper dose-fractionation schemes.

Socioeconomic and demographic determinants of radiation treatment and outcomes in glioblastoma patients

Introduction

Poor outcomes in glioblastoma patients, despite advancing treatment paradigms, indicate a need to determine non-physiologic prognostic indicators of patient outcome. The impact of specific socioeconomic and demographic patient factors on outcomes is unclear. We sought to identify socioeconomic and demographic patient characteristics associated with patient survival and tumor progression, and to characterize treatment options and healthcare utilization.

Methods

A cohort of 169 patients with pathologically confirmed glioblastomas treated at our institution was retrospectively reviewed. Multivariable cox proportional hazards analysis for overall survival (OS) and cumulative incidence of progression was performed. Differences in treatment regimen, patient characteristics, and neuro-oncology office use between different age and depressive disorder history patient subgroups were calculated two-sample t-tests, Fisher's exact tests, or linear regression analysis.

Results

The median age of all patients at the time of initiation of radiation therapy was 60.5 years. The median OS of the cohort was 13.1 months. Multivariable analysis identified age (Hazard Ratio 1.02, 95% CI 1.00–1.04) and total resection (Hazard Ratio 0.52, 95% CI 0.33–0.82) as significant predictors of OS. Increased number of radiation fractions (Hazard Ratio 0.90, 95% CI 0.82–0.98), depressive disorder history (Hazard Ratio 0.59, 95% CI 0.37–0.95), and total resection (Hazard Ratio 0.52, 95% CI 0.31–0.88) were associated with decreased incidence of progression. Notably, patients with depressive disorder history were observed to have more neuro-oncology physician office visits over time (median 12 vs. 16 visits, p = 0.0121). Patients older than 60 years and those with Medicare (vs. private) insurance were less likely to receive as many radiation fractions (p = 0.0014) or receive temozolomide concurrently with radiation (Odds Ratio 0.46, p = 0.0139).

Conclusion

Older glioblastoma patients were less likely to receive as diverse of a treatment regimen as their younger counterparts, which may be partially driven by insurance type. Patients with depressive disorder history exhibited reduced incidence of progression, which may be due to more frequent health care contact during neuro-oncology physician office visits.

Neutrophilia and post-radiation thrombocytopenia predict for poor prognosis in radiation-treated glioma patients

Introduction

Poor outcomes in glioma patients indicate a need to determine prognostic indicators of survival to better guide patient specific treatment options. While preoperative neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and monocyte-to-lymphocyte ratio (MLR) have been suggested as prognostic systemic inflammation markers, the impact of post-radiation changes in these cell types is unclear. We sought to identify which hematologic cell measurements before, during, or after radiation predicted for patient survival.

Methods

A cohort of 182 patients with pathologically confirmed gliomas treated at our institution was retrospectively reviewed. Patient blood samples were collected within one month before, during, or within 3 months after radiation for quantification of hematologic cell counts, for which failure patterns were evaluated. Multivariable cox proportional hazards analysis for overall survival (OS) and progression-free survival (PFS) was performed to control for patient variables.

Results

Multivariable analysis identified pre-radiation NLR > 4.0 (Hazard ratio = 1.847, p = 0.0039) and neutrophilia prior to (Hazard ratio = 1.706, p = 0.0185), during (Hazard ratio = 1.641, p = 0.0277), or after (Hazard ratio = 1.517, p = 0.0879) radiation as significant predictors of worse OS, with similar results for PFS. Post-radiation PLR > 200 (Hazard ratio = 0.587, p = 0.0062) and a percent increase in platelets after radiation (Hazard ratio = 0.387, p = 0.0077) were also associated with improved OS. Patients receiving more than 15 fractions of radiation exhibited greater post-radiation decreases in neutrophil and platelet counts than those receiving fewer. Patients receiving dexamethasone during radiation exhibited greater increases in neutrophil counts than those not receiving steroids. Lymphopenia, changes in lymphocyte counts, monocytosis, MLR, and changes in monocyte counts did not impact patient survival.

Conclusion

Neutrophilia at any time interval surrounding radiotherapy, pre-radiation NLR, and post-radiation thrombocytopenia, but not lymphocytes or monocytes, are predictors of poor patient survival in glioma patients.

Ablative radiotherapy in oligometastatic pancreatic cancer to delay polyprogression, limit chemotherapy, and improve outcomes

PURPOSE

The oligometastatic state is observed in patients across many malignancies, with increased recognition regarding improved outcomes after local therapies. However, there is limited data specifically regarding pancreatic ductal adenocarcinoma (PDAC). We hypothesized that an oligometastatic pancreatic ductal adenocarcinoma (OPanc) phenotype would benefit from stereotactic ablative radiotherapy (SABR) to all active metastatic sites. Here, we report our institutional experience of SABR-treated OPanc to evaluate the feasibility of the approach.

METHODS AND MATERIALS

A retrospective review of patients with synchronous or metachronous OPanc (one to five metastases) who received SABR to all active metastatic sites was performed. We identified a comparable group of patients with similar metastatic burden, range of CA19-9 levels, and no progression for at least five months who did not receive SABR. We compared overall survival as the primary outcome, and polyprogression-free survival and time off chemotherapy as the secondary exploratory assessments. A third group presenting with stage IV PDAC and more than five distant lesions (polymetastatic) was identified to help define expected outcomes after polyprogression.

RESULTS

Our study included 20 patients with OPanc receiving SABR and 21 who did not. SABR was delivered to 38 metastatic tumors. Out of the 20 SABR-treated OPanc patients, 17 (85%) had six or more months of time off chemotherapy, compared to seven patients (33.3%) among the chemotherapy-treated group. Median polyprogression-free survival was 40 and 14 months (hazard ratio= 0.2, 95% confidence interval 0.07-0.54, p-value= 0.0009), and overall survival was 42 and 18 months (hazard ratio= 0.21, 95% confidence interval 0.08-0.53, p-value= 0.0003), for SABR and chemotherapy-treated cohorts, respectively.

CONCLUSIONS

Management of OPanc with SABR as local regional therapy could improve outcomes in a selected population and warrants prospective evaluation.

Combining Serial and Parallel Functionality in Functional Lung Avoidance Radiation Therapy

PURPOSE

Functional lung avoidance (FLA) radiation therapy (RT) aims to minimize post-RT pulmonary toxicity by preferentially avoiding dose to high-functioning lung (HFL) regions. A common limitation is that FLA approaches do not consider the conducting architecture for gas exchange. We previously proposed the functionally weighted airway sparing (FWAS) method to spare airways connected to HFL regions, showing that it is possible to substantially reduce risk of radiation-induced airway injury. Here, we compare the performance of FLA and FWAS and propose a novel method combining both approaches.

METHODS

We used breath-hold computed tomography (BHCT) and simulation 4-dimensional computed tomography (4DCT) from 12 lung stereotactic ablative radiation therapy patients. Four planning strategies were examined: (1) Conventional: no sparing other than clinical dose-volume constraints; (2) FLA: using a 4DCT-based ventilation map to delineate the HFL, plans were optimized to reduce mean dose and V_13.50 in HFL; (3) FWAS: we autosegemented 11 to 13 generations of individual airways from each patient's BHCT and assigned priorities based on the relative contribution of each airway to total ventilation. We used these priorities in the optimization along with airway dose constraints, estimated as a function of airway diameter and 5% probability of collapse; and (4) FLA + FWAS: we combined information from the 2 strategies. We prioritized clinical dose constraints for organs at risk and planning target volume in all plans. We performed the evaluation in terms of ventilation preservation accounting for radiation-induced damage to both lung parenchyma and airways.

RESULTS

We observed average ventilation preservation for FLA, FWAS, and FLA + FWAS as 3%, 8.5%, and 14.5% higher, respectively, than for Conventional plans for patients with ventilation preservation in Conventional plans <90%. Generalized estimated equations showed that all improvements were statistically significant (P ≤ .036). We observed no clinically relevant improvements in outcomes of the sparing techniques in patients with ventilation preservation in Conventional plans ≥90%.

CONCLUSIONS

These initial results suggest that it is crucial to consider the parallel and the serial nature of the lung to improve post-radiation therapy lung function and, consequently, quality of life for patients.

Dose-Intensified Stereotactic Ablative Radiation for Localized Prostate Cancer

Purpose

Stereotactic ablative radiation (SAbR) has been increasingly used in prostate cancer (PCa) given its convenience and cost efficacy. Optimal doses remain poorly defined with limited prospective comparative trials and long-term safety/efficacy data at higher dose levels. We analyzed toxicity and outcomes for SAbR in men with localized PCa at escalated 45 Gy in 5 fractions.

Methods and Materials

This study retrospectively analyzed men from 2015 to 2019 with PCa who received linear-accelerator-based SAbR to 45 Gy in 5 fractions, along with perirectal hydrogel spacer, fiducial placement, and MRI-based planning. Disease control outcomes were calculated from end of treatment. Minimally important difference (MID) assessing patient-reported quality of life was defined as greater than a one-half standard deviation increase in American Urological Association (AUA) symptom score after SAbR.

Results

Two-hundred and forty-nine (249) low-, intermediate-, and high-risk PCa patients with median follow-up of 14.9 months for clinical toxicity were included. Acute urinary grade II toxicity occurred in 20.4% of patients. Acute grade II GI toxicity occurred in 7.3% of patients. For follow-up > 2 years (n = 69), late GU and GI grade ≥III toxicity occurred in 5.8% and 1.5% of patients, respectively. MID was evident in 31.8%, 23.4%, 35.8%, 37.0%, 33.3%, and 26.7% of patients at 3, 6, 12, 24, 36, and 48 months, respectively. The median follow-up for biochemical recurrence was 22.6 months with biochemical failure-free survival of 100% at 1 year (n = 226) and 98.7% for years 2 (n = 113) and 3 (n = 54).

Conclusions

SAbR for PCa at 45 Gy in 5 fractions shows an encouraging safety profile. Prospective studies with longer follow-up are warranted to establish this dose regimen as standard of care for PCa.

Discordance of patient- and physician-reported toxicities in two prospective trials of stereotactic body radiotherapy (SBRT) for localized prostate cancer

245

Background: SBRT for localized prostate cancer (PCa) is the focus of several ongoing and reported high-impact trials, which often focus on physician-reported toxicity (P-Tox) when comparing regimens. Patient-reported quality of life (PR-QoL) may differ and provide a more sensitive comparative metric of treatment burden, especially with fewer provider interactions during SBRT than during protracted RT courses. We evaluated the concordance of prospective genitourinary (GU) and gastrointestinal (GI) P-Tox and PR-QOL in men receiving SBRT for PCa. Methods: Data from two concurrently-enrolled prospective trials of SBRT in high-risk (Phase I Safety Endpoint, NCT01896271) and low-intermediate risk (Phase II GI Toxicity Endpoint, NCT02353832) PCa were used. Matching standardized schedules of collected PR-QoL [Expanded Prostate Cancer Index Composite (EPIC)] and P-Tox (CTCAE v5.0) were analyzed over the first 18 months of follow up, where symptoms are most pronounced. We assessed concordance of Grade≥2 GU/GI physician reported toxicity with PR-QoL declines exceeding anchor based minimal clinically important difference (MCID) thresholds (-6 urinary and -5 bowel summary scores, respectively) for each patient at each time point. Patients without baseline PR-QoL data were excluded in full, while time points with missing PR-QoL or P-Tox were excluded individually without imputation. Concordance was evaluated by Cohen’s kappa statistic. Results: From 101 patients, there were 256 (64%) follow up observations through 18 months with both PR-QoL and P-Tox at the time point and baseline. Concordance of PR-QoL and P-Tox was low at all time points for both GU and GI toxicity domains (mean kappa 0.093; Table). MCID was more often reported by patients than Grade≥2 toxicity by physicians (38% vs 17% for GU and 44% vs 10% for GI). There was little overlap of PR-QoL and P-Tox reporting: Grade≥2 P-Tox reported in 17% of observations with MCID in PR-QoL, while MCID in PR-QoL reported in 54% of observations of Grade ≥2 P-Tox. Mean concordance was similarly low when analyzing sub-groups of trial, investigator, and an alternative 2xMCID threshold. Conclusions: P-Tox and PR-QoL differed dramatically in two prospective studies of SBRT despite toxicity primary endpoints. This may reflect subjective and varying intervention thresholds driving P-Tox reporting, rather than actual patient burden. These data strongly support use of PR-QoL rather than P-Tox for SBRT comparative study endpoints and guidelines in this rapidly evolving space. [Table: see text]

Can stereotactic ablative radiotherapy for oligometastatic pancreatic cancer help avoid perpetual chemotherapy and improve outcomes?

571

Background: The oligometastatic state is increasing recognized and improved outcomes after local regional therapies have been observed in many malignancies, however there is a paucity of data on outcomes of patients with limited extent pancreatic ductal adenocarcinoma (PDAC). We hypothesize oligometastatic pancreatic cancer (OPanc) with 1-5 metastases would benefit from stereotactic ablative radiotherapy (SABR) to all active sites of disease, can improve outcome, and offer time off chemotherapy. Here in, we report our institutional experience of treating OPanc with SABR to evaluate the outcome and feasibility of the approach and compare outcomes with other institutional cohorts. Methods: A retrospective review was conducted on patients with stage IV PDAC who received SABR after noted to have OPanc. Patients with a histological diagnosis of PDAC, number of metastases ranging between 1-5, and who received SABR to all active disease at time of treatment were included. We identified a comparable group of 16 patients with similar metastatic burden but did not receive SABR. Overall survival and time off chemotherapy were evaluated in addition to assessment of each patients’ disease course. Results: Fourteen patients met the inclusion criteria. Five patients had metastases confined to lung only and nine to the liver only. Median baseline CA 19-9 was 105 U/mL (range < 1, 921 U/mL). Eight patients had metachronous OPanc diagnosis. SABR was delivered to 22 metastatic tumors. Median progression free and overall survivals were 25 and 12.8 months, and 46 and 14.5 months for the SABR treated and the chemotherapy cohorts respectively. A total of 85.7% of patients that received SABR had a chemotherapy treatment break of greater than 6 months. Conclusions: Management of OPanc (1-5 lesions) with SABR as local regional therapy could improve outcomes in this selected population and warrants prospective evaluation.

Outcome and Immune Correlates of a Phase II Trial of High-Dose Interleukin-2 and Stereotactic Ablative Radiotherapy for Metastatic Renal Cell Carcinoma

PURPOSE

This phase II clinical trial evaluated whether the addition of stereotactic ablative radiotherapy (SAbR), which may promote tumor antigen presentation, improves the overall response rate (ORR) to high-dose IL2 (HD IL2) in metastatic renal cell carcinoma (mRCC).

PATIENTS AND METHODS

Patients with pathologic evidence of clear cell renal cell carcinoma (RCC) and radiographic evidence of metastasis were enrolled in this single-arm trial and were treated with SAbR, followed by HD IL2. ORR was assessed based on nonirradiated metastases. Secondary endpoints included overall survival (OS), progression-free survival (PFS), toxicity, and treatment-related tumor-specific immune response. Correlative studies involved whole-exome and transcriptome sequencing, T-cell receptor sequencing, cytokine analysis, and mass cytometry on patient samples.

RESULTS

Thirty ethnically diverse mRCC patients were enrolled. A median of two metastases were treated with SAbR. Among 25 patients evaluable by RECIST v1.1, ORR was 16% with 8% complete responses. Median OS was 37 months. Treatment-related adverse events (AE) included 22 grade ≥3 events that were not dissimilar from HD IL2 alone. There were no grade 5 AEs. A correlation was observed between SAbR to lung metastases and improved PFS (P = 0.0165). Clinical benefit correlated with frameshift mutational load, mast cell tumor infiltration, decreased circulating tumor-associated T-cell clones, and T-cell clonal expansion. Higher regulatory/CD8⁺ T-cell ratios at baseline in the tumor and periphery correlated with no clinical benefit.

CONCLUSIONS

Adding SAbR did not improve the response rate to HD IL2 in patients with mRCC in this study. Tissue analyses suggest a possible correlation between frameshift mutation load as well as tumor immune infiltrates and clinical outcomes.

SAbR for High-Risk Prostate Cancer-A Prospective Multilevel MRI-Based Dose Escalation Trial

PURPOSE

Radiation dose intensification improves outcome in men with high-risk prostate cancer (HR-PCa). A prospective trial was conducted to determine safety, feasibility, and maximal tolerated dose of multilevel magnetic resonance imaging (MRI)-based 5-fraction SAbR in patients with HR-PCa.

METHODS AND MATERIALS

This phase I clinical trial enrolled patients with HR-PCa with grade group ≥4, prostate-specific antigen (PSA) ≥20 ng/mL, or radiographic ≥T3, and well-defined prostatic lesions on multiparametric MRI (mpMRI) into 4 dose-escalation cohorts. The initial cohort received 47.5 Gy to the prostate, 50 Gy to mpMRI-defined intraprostatic lesion(s), and 22.5 Gy to pelvic lymph nodes in 5 fractions. Radiation doses were escalated for pelvic nodes to 25 Gy and mpMRI lesion(s) to 52.5 Gy and then 55 Gy. Escalation was performed sequentially according to rule-based trial design with 7 to 15 patients per cohort and a 90-day observation period. All men received peri-rectal hydrogel spacer, intraprostatic fiducial placement, and 2 years of androgen deprivation. The primary endpoint was maximal tolerated dose according to a 90-day acute dose-limiting toxicity (DLT) rate <33%. DLT was defined as National Cancer Institute Common Toxicity Criteria for Adverse Events ≥grade 3 treatment-related toxicity. Secondary outcomes included acute and delayed gastrointestinal (GI)/genitourinary (GU) toxicity graded with Common Toxicity Criteria for Adverse Events.

RESULTS

Fifty-five of the 62 enrolled patients were included in the analysis. Dose was escalated through all 4 cohorts without observing any DLTs. Median overall follow-up was 18 months, with a median follow-up of 42, 24, 12, and 7.5 months for cohorts 1 to 4 respectively. Acute and late grade 2 GU toxicities were 25% and 20%, while GI were 13% and 7%, respectively. Late grade 3 GU and GI toxicities were 2% and 0%, respectively.

CONCLUSIONS

SAbR dose for HR-PCa was safely escalated with multilevel dose painting of 47.5 Gy to prostate, 55 Gy to mpMRI-defined intraprostatic lesions, and 25 Gy to pelvic nodal region in 5 fractions. Longer and ongoing follow-up will be required to assess late toxicity.

Preliminary Results of Multi-Institutional Phase 1 Dose Escalation Trial Using Single-Fraction Stereotactic Partial Breast Irradiation for Early Stage Breast Cancer

PURPOSE

We report on our early experience of our prospective multicenter phase 1 dose- escalation study of single-fraction stereotactic partial breast irradiation (S-PBI) for early stage breast cancer after partial mastectomy using a robotic stereotactic radiation system.

METHODS AND MATERIALS

Thirty women with in situ or invasive breast cancer stage 0, I, or II with tumor size <3 cm treated with lumpectomy were enrolled in this phase 1 single-fraction S-PBI dose-escalation trial. Women received either 22.5, 26.5, or 30 Gy in a single fraction using a robotic stereotactic radiation system. The primary outcome was to reach tumoricidal dose of 30 Gy in a single fraction to the lumpectomy cavity without exceeding the maximum tolerated dose. Secondary outcomes were to determine dose-limiting toxicity and cosmesis. Tertiary goals were ipsilateral breast recurrence rate, distant disease-free interval, recurrence-free survival, and overall survival.

RESULTS

From June 2016 to January 2021, 11, 8, and 10 patients were treated to doses of 22.5, 26.5, or 30 Gy in a single fraction, respectively, with median follow-up being 47.9, 25.1, and 16.2 months. No patients experienced acute (<90 days) grade 3 or higher treatment-related toxicity, and maximum tolerated dose was not reached. There were 2 delayed grade 3 toxicities. Four patients (13.8%) developed fat necrosis across all 3 cohorts, which compares favorably with results from other PBI trials. No dose cohort had a statistically significant cosmetic detriment from baseline to 12 months or 24 months follow-up by patient- or physician-reported global cosmetic scores. There were no reports of disease recurrence.

CONCLUSIONS

This phase 1 trial demonstrates that S-PBI can be used to safely escalate dose to 30 Gy in a single fraction with low toxicity and without detriment in cosmesis relative to baseline.

A Multi-Institutional Phase 2 Trial of High-Dose SAbR for Prostate Cancer Using Rectal Spacer

PURPOSE

High-dose SABR for prostate cancer offers the radiobiologic potency of the most intensified radiation therapy regimens but was associated with >90% rates of ulceration of the anterior rectal wall on endoscopic assessment; this infrequently progressed to severe rectal toxicity in prior prospective series. A multi-institutional phase 2 prospective trial was conducted to assess whether placement of a perirectal hydrogel spacer would reduce acute periprostatic rectal ulcer events after high-dose (>40 Gy) SABR.

METHODS AND MATERIALS

Eligible patients included men with stage ≤T2c localized grade group 1 to 3 prostate cancer, a prostate-specific antigen (PSA) level ≤15 ng/mL, American Urological Association Symptom Index = AUA-SI scores ≤18, and a gland volume ≤80 cm³. Patients underwent perirectal hydrogel spacer placement, followed by SABR of 45 Gy in 5 fractions every other day to the prostate only. Androgen deprivation was not allowed except for cytoreduction. The rectal wall was directly assessed by serial anoscopy during follow-up to determine whether the spacer would reduce acute periprostatic rectal ulcer events from >90% to <70% within 9 months of treatment.

RESULTS

Forty-four men were enrolled and 43 were eligible for protocol analysis. The median follow-up for surviving patients was 48 months. Acute periprostatic ulcers were observed in 6 of 42 patients (14.3%; 95% confidence interval, 6.0%-27%; P < .001) at a median of 2.9 months posttreatment (range, 1.7-5.6 months). All ulcers (grade 1, 5 ulcers; grade 2, 1 ulcer) resolved on repeat anoscopy within 8 months of incidence. There were no grade ≥3 late gastrointestinal toxicities; the incidence of late grade-2 gastrointestinal toxicities was 14.3%, with a prevalence at 3 years of 0%. No toxicities greater than grade 3 occurred in any domain. Four-year freedom from biochemical failure was 93.8% (95% CI, 85.2%-100.0%).

CONCLUSIONS

Temporary hydrogel spacer placement before high-dose SABR treatment for localized prostate cancer and use of strict dose constraints are associated with a significant reduction in the incidence of rectal ulcer events compared with prior phase 1/2 trial results.

Hydrogel Spacer Rectal Wall Infiltration Associated With Severe Rectal Injury and Related Complications After Dose Intensified Prostate Cancer Stereotactic Ablative Radiation Therapy

The risk of rectal toxicity during and after prostate cancer radiation therapy is common to all treatment regimens. Hydrogel rectal spacers are increasingly being used to mitigate this risk and to facilitate dose-escalation, but also may infiltrate the rectal wall, with unclear clinical implication. We present a case of significant infiltration associated with severe late rectal injury (grade 4) and further grade 3 to 4 sequelae (recto-urethral fistula and associated osteomyelitis requiring exenteration) after high-dose stereotactic body radiation therapy for localized prostate cancer. The injury's temporal pattern associated with the expected timing of gel dissolution and displacement of infiltrated rectal layers potentially toward high dose regions together suggest a contributing role of the infiltration to the injury. In light of the rapid increase of hydrogel rectal spacer utilization, we review the case's evolution, concerning imaging findings, and associated literature and make suggestions regarding treatment planning and endoscopic assessment in the setting of infiltration or expected injury.

Phase II trial of stereotactic ablative radiation (SAbR) for oligoprogressive kidney cancer

4564

Background: Metastatic renal cell carcinoma (mRCC) patients on systemic therapy may experience oligoprogression. SAbR has been demonstrated to be safe and is associated with high local control rates in mRCC. In this prospective phase II single arm trial, we investigated SAbR to control oligoprogressive mRCC. Methods: Patients with mRCC who demonstrated response to systemic therapy with subsequent radiographic evidence of three or fewer sites of progression were treated with SAbR to all progressive sites. Systemic therapy was held during SAbR at the discretion of the treating oncologist. Follow-up included radiographic imaging at three-month intervals. Sequential SAbR for continued oligoprogression was allowed. The primary objective was extension of ongoing systemic therapy by >6 months in 40% of the patients. Progression was defined by any of these 3 criteria: (1) local failure at a radiated site; (2) progression ineligible for additional SAbR (>3 sites) or involving >30% of metastasis; or (3) progression as clinically determined by treating physicians. An exact binomial test was used to test the probability of postponing systemic therapy. Secondary endpoints focused on overall survival (OS), local control (LC) rates, toxicity, and health-related quality of life (QOL). Results: The trial completed accrual with enrollment of 20 patients who received SAbR to a total of 36 sites. At enrollment four, twelve, three, and one patients were on first, second, third, and fourth line of systemic therapy, respectively. Eleven were on immunotherapy and nine on a tyrosine-kinase inhibitor. Three patients required repeat SAbR to a new site for sequential disease control. At a median follow-up of 8.3 months (interquartile range 3.9 – 15.1), SAbR extended the duration of the ongoing systemic therapy by >6 months in 12 out of 17 patients (70.6%, 95% CI: 48.9%-92.3%). Thirteen out of 20 patients progressed with a median PFS of 8.7 months (95% CI: 3.2-12.4). Five patients died and the OS did not reach the median. LC was 36/36 (100%). Treatment related grade 1 and grade 2 toxicity was experienced by three and one patient, respectively; no grade 3 toxicities were reported. When compared to baseline, no significant decline in QOL was detected. Conclusions: SAbR extended PFS of ongoing systemic by >6 months in oligoprogressive patients with mRCC. SAbR was safe and did not adversely affect QOL. These data support further evaluation of SAbR for oligoproressive mRCC in a prospective randomized setting. Clinical trial information: NCT03696277.

Phase II trial of clinical activity and safety of ceritinib combined with stereotactic ablative radiotherapy (SABR) in lung adenocarcinoma patients

e21571

Background: ALK -targeting drugs and SABR are combined in patients with metastatic cancer, anecdotally yielding clinical benefit. However, the precise impact of the combination and the optimal time to introduce SABR remain unknown. Methods: This completed phase 2 study (NCT02513667) had a primary objective of doubling progression free survival (PFS) for ALK+ lung adenocarcinoma patients by consolidating all remaining disease with SABR, 8-10 weeks after ceritinib initiation. Patients who then progressed could receive repeat SABR as long as they then resumed ceritinib. Patients were divided into ALK-inhibitor naïve vs previously treated cohorts. Oligometastatic disease was NOT a requirement for study entry, CNS disease was permitted. Blood was serially analyzed for variation in 1. blood cfDNA detection of resistance mechanisms 2. flow cytometric analysis of white cell populations. Results: 14 patients were enrolled out of a planned 33; 7 female; 3 hispanic/latino; median age was 53 years (range 31-78); 5 patients had previously received crizotinib. 4 patients stopped ceritinib within 30 days due to toxicity, despite dose reductions or with-food administration. However, all patients still completed initial SABR consistent with protocol time-points. Patients predominantly had thoracic disease irradiated (11/14, 78%). Two patients had only brain metastases treated and 1 had bone only metastases treated. 4 had one fraction SBRT regimens (16-24 Gy per fraction) delivered to disease, 3 had three fraction SBRT regimens (9-11 Gy per fraction) delivered to disease, and 7 had five fraction SBRT or 15 fraction hypofractionated regimens (6 Gy per fraction or 3Gy per fraction, respectively) delivered to disease. Disease control in all irradiated areas was 100%. There was no significant grade 3 or higher toxicity associated with radiation. Broad variability in baseline and serial levels of circulating PMN-MDSC, VEGFR2, FoxP3+, CD56+CD16+ and various T-cell populations showed no clinical correlation. The trial terminated early due to increased use of alternative targeted therapies, thus the primary endpoint was not met. 8 patients had CR/PR/SD as best response. Including those who did not tolerate ceritinib, median PFS was 12 months, max of 31 months with 1 ongoing response. Conclusions: Consolidative SABR after ALK therapy is well tolerated, can be repeated and may prolong PFS compared to drug alone. Ceritinib toxicity meant higher rates of discontinuation but this did not prevent consolidative SABR in any patient. Clinical trial information: NCT02513667.

Fundamentals of Radiation Oncology for Neurologic Imaging

Although the physical and biologic principles of radiation therapy have remained relatively unchanged, a technologic renaissance has led to continuous and ever-changing growth in the field of radiation oncology. As a result, medical devices, techniques, and indications have changed considerably during the past 20-30 years. For example, advances in CT and MRI have revolutionized the treatment planning process for a variety of central nervous system diseases, including primary and metastatic tumors, vascular malformations, and inflammatory diseases. The resultant improved ability to delineate normal from abnormal tissue has enabled radiation oncologists to achieve more precise targeting and helped to mitigate treatment-related complications. Nevertheless, posttreatment complications still occur and can pose a diagnostic challenge for radiologists. These complications can be divided into acute, early-delayed, and late-delayed complications on the basis of the time that they manifest after radiation therapy and include leukoencephalopathy, vascular complications, and secondary neoplasms. The different irradiation technologies and applications of these technologies in the brain, current concepts used in treatment planning, and essential roles of the radiation oncologist in the setting of brain disease are reviewed. In addition, relevant imaging findings that can be used to delineate the extent of disease before treatment, and the expected posttreatment imaging changes are described. Common and uncommon complications related to radiation therapy and the associated imaging manifestations also are discussed. Familiarity with these entities may aid the radiologist in making the diagnosis and help guide appropriate management. ^©RSNA, 2020.

Safety and outcome of stereotactic body radiation therapy (SBRT) with rectal hydrogel spacer for prostate cancer

76

Background: Ultra-hypofractionated radiotherapy delivered using stereotactic body radiotherapy (SBRT) is a cost-effective treatment for localized prostate cancer. Optimal dosing remains unclear, as commonly used 30-40Gy/5fx regimens appear to overestimate hypofractionation’s control benefits. Here, we report the largest experience of 45Gy/5Fx of SBRT for prostate cancer patients treated with hydrogel peri-rectal spacer (‘hydrogel’). Methods: An IRB-approved retrospective protocol was used to conduct a registry search identifying all patients with prostate cancer who received 45Gy/5Fx between 2015-2019 with hydrogel. Genitourinary (GU) and gastrointestinal (GI) toxicities were defined using the NCI Common Toxicity Criteria for Adverse Events (CTCAE) v.5.0. The ASTRO-Phoenix failure definition of Nadir+2 ng/mL was used for biochemical failure. Results: We analyzed 250 low (9.2%), intermediate (85.2%), and high-risk (5.6%) prostate cancer patients with a median follow-up of 9.9 months (range: 0-45.7 months). Acute GU and GI grade ≥ II toxicities were noted in 15.2% and 7.2% of patients, respectively. Late GU grade II and III toxicities occurred in 24.0% and 1.2% of patients, respectively, while late GI grade II and III toxicities occurred in 4.0% and 0.4% of patients, respectively. In patients (N=44) with follow-up >2 years, late GU and GI grade III toxicities occurred in 4.55% and 2.27% of patients, respectively. A significant correlation was noted for acute GI and GU toxicity predicting the respective late GI and GU toxicity (p-value < 0.001 for both). Physician-reported Grade ≥ II new onset erectile dysfunction was 17.2%. A gradual decline in prostate-specific antigen with a mean nadir of 0.04 (95% CI: [0.018, 0.067]) at 36 months was noted. The actuarial freedom from biochemical failure was 96.33% at 3 years. Overall survival was 94.09% at 3 years with no deaths attributed to prostate cancer. Conclusions: SBRT treatment of 45Gy/5Fx with hydrogel is well tolerated with GU/GI toxicities comparable to those reported for conventional fractionation. Although short, the 3-year biochemical control rate is encouraging. Longer follow-up and prospective evaluation are warranted.

Prostate oncologic therapy while ensuring neurovascular conservation (POTEN-C): A phase II randomized controlled trial of stereotactic ablative body radiotherapy (SAbR) with or without neurovascular sparing for erectile function preservation in localized prostate cancer

TPS381

Background: Radiotherapy (RT) associated sexual dysfunction occurs in half of men following treatment for localized prostate cancer. Proposed mechanisms include vascular injury of adjacent internal pudendal arteries (IPA), penile bulb (PB), corpora cavernosa (CC) or neurovascular bundles (NVB). Ability to spare these structures has been limited by a presumed need to treat the entire prostate gland, while also preventing rectal injury. Recent innovations have challenged this issue: a) precise dose delivery with stereotactic ablative RT (SAbR), b) improved spatial mapping of clinically significant disease with mpMRI, c) rectal avoidance with rectal spacer use. Methods: POTEN-C is a multi-center phase II randomized control trial, which includes men with a) low-intermediate risk prostate cancer eligible for SAbR without ADT, b) potent by sexual composite score ≥60 on EPIC patient-reported quality of life instrument, c) mpMRI delineated disease (PIRADS v2 score 3-5) ≥5mm to at least one ‘spared’ NVB. After placement of rectal spacer gel and CT/MRI simulation, men are randomized to standard SAbR to 40-45Gy/5fx or neurovascular-sparing SAbR. In the sparing experimental arm, the prostate PTV is given 30Gy/5fx excluding unilateral ‘spared’ NVB, while a 40-45Gy PTV further excludes a 5mm protective shell on the unilateral ‘spared’ NVB+IPA+PB+CC. Centralized rapid review of initial contours/plans and online training materials are integrated. The primary endpoint is 2-year patient-reported potency, measured by EPIC sexual composite score. We hypothesize that neurovascular sparing SAbR will reduce 2-year EPIC score decline from a control of 20 to 10 (corresponding to a MCID). Assuming standard deviation 20, two-sided significance level 0.10 with two-sample t-testing, and 15% attrition, we intend to enroll 120 patients to provide 80% power to detect this difference. Secondary endpoints include sexual medication/aid use, relapse rates, GU/GI toxicity. Enrollment is ongoing. Details: http://www.poten-c.org . Clinical trial information: 03525262.

Stereotactic Body Radiation Therapy for Operable Early-Stage Lung Cancer: Findings From the NRG Oncology RTOG 0618 Trial

Importance

Stereotactic body radiation therapy (SBRT) has become a standard treatment for patients with medically inoperable early-stage lung cancer. However, its effectiveness in patients medically suitable for surgery is unclear.

Objective

To evaluate whether noninvasive SBRT delivered on an outpatient basis can safely eradicate lung cancer and cure selected patients with operable lung cancer, obviating the need for surgical resection.

Design, Setting, and Participants

Single-arm phase 2 NRG Oncology Radiation Therapy Oncology Group 0618 study enrolled patients from December 2007 to May 2010 with median follow-up of 48.1 months (range, 15.4-73.7 months). The setting was a multicenter North American academic and community practice cancer center consortium. Patients had operable biopsy-proven peripheral T1 to T2, N0, M0 non-small cell tumors no more than 5 cm in diameter, forced expiratory volume in 1 second (FEV1) and diffusing capacity greater than 35% predicted, arterial oxygen tension greater than 60 mm Hg, arterial carbon dioxide tension less than 50 mm Hg, and no severe medical problems. The data analysis was performed in October 2014.

Interventions

The SBRT prescription dose was 54 Gy delivered in 3 18-Gy fractions over 1.5 to 2.0 weeks.

Main Outcomes and Measures

Primary end point was primary tumor control, with survival, adverse events, and the incidence and outcome of surgical salvage as secondary end points.

Results

Of 33 patients accrued, 26 were evaluable (23 T1 and 3 T2 tumors; 15 [58%] male; median age, 72.5 [range, 54-88] years). Median FEV1 and diffusing capacity of the lung for carbon monoxide at enrollment were 72.5% (range, 38%-136%) and 68% (range, 22%-96%) of predicted, respectively. Only 1 patient had a primary tumor recurrence. Involved lobe failure, the other component defining local failure, did not occur in any patient, so the estimated 4-year primary tumor control and local control rate were both 96% (95% CI, 83%-100%). As per protocol guidelines, the single patient with local recurrence underwent salvage lobectomy 1.2 years after SBRT, complicated by a grade 4 cardiac arrhythmia. The 4-year estimates of disease-free and overall survival were 57% (95% CI, 36%-74%) and 56% (95% CI, 35%-73%), respectively. Median overall survival was 55.2 months (95% CI, 37.7 months to not reached). Protocol-specified treatment-related grade 3, 4, and 5 adverse events were reported in 2 (8%; 95% CI, 0.1%-25%), 0, and 0 patients, respectively.

Conclusions and Relevance

As given, SBRT appears to be associated with a high rate of primary tumor control, low treatment-related morbidity, and infrequent need for surgical salvage in patients with operable early-stage lung cancer.

Trial Registration

ClinicalTrials.gov Identifier: NCT00551369.