Use of Focal Radiotherapy Boost for Prostate Cancer and Perceived Barriers toward its Implementation: A Survey

PURPOSE/OBJECTIVE(S)

In a recent phase III randomized control trial (FLAME), delivering a focal radiotherapy (RT) boost to tumors visible on MRI was shown to improve outcomes for prostate cancer patients without increasing toxicity. The aim of this study was to assess how widely this technique is being applied in current practices worldwide as well as physicians' perceived barriers toward its implementation.

MATERIALS/METHODS

An online survey assessing the use of intraprostatic focal boost was conducted in December 2022 and February 2023. The survey link was distributed to radiation oncologists worldwide via email list, group text platform, and social media. Survey questions included how many prostate cancer cases participants treat in a typical month; how often they use focal boost, if at all; the degree to which their practice is genitourinary (GU)-subspecialized; main barriers to implementing focal boost more often in their practice; and demographic information. Subgroup analyses were also conducted for participants from high-income or low-to-middle-income countries, as defined by the World Bank.

RESULTS

The survey initially collected 205 responses from various countries over a two-week period in December 2022. The survey was then reopened for one week in February 2023 to allow for more participation, leading to a total of 263 responses. The highest-represented countries were the United States (42%), Mexico (13%), and the United Kingdom (8%). The majority of respondents worked at an academic medical center (52%) and considered their practice to be at least partially GU-subspecialized (74%). 57% of participants overall reported not routinely using intraprostatic focal boost. Even among complete subspecialists, a substantial proportion (39%) do not routinely use focal boost. Less than half of participants in both high-income and low-to-middle-income countries were shown to routinely use focal boost. Perceived barriers to implementation are shown in Table 1.

CONCLUSION

Despite the promising level 1 results of the FLAME trial, many radiation oncologists worldwide are not routinely offering focal RT boost. Adoption of this technique might be accelerated by increased access to high-quality MRI, better registration algorithms of MRI to CT simulation images, physician education on benefit-to-harm ratio, automated planning algorithms, and physician training on contouring prostate lesions on MRI.

Consolidative Radiotherapy for Residual PET-Avid Disease on Day +30 Post CAR T-Cell Therapy in Non-Hodgkin Lymphoma

PURPOSE/OBJECTIVE(S)

Up to30% of non-Hodgkin lymphoma (NHL) patients achieve a partial response (PR) to anti-CD19 Chimeric Antigen Receptor T-cell Therapy (CART) on day +30. Most PR patients relapse and only 30% achieve spontaneous complete response (CR) without additional therapies. This study is the first to report on the role of consolidative radiotherapy (cRT) for PR PET-avid disease on day +30 post-CART in NHL.

MATERIALS/METHODS

Aretrospective review across 3 institutions from 2018 to 2022 identified 60 patients with B-cell NHL who received CART and achieved PR (Deauville 4-5) with <5 PET-avid disease sites on day +30. Progression-free survival (PFS) was defined from CART infusion to any disease progression. Overall survival (OS) was defined from CART infusion to death. Local relapse-free survival (LRFS), calculated based on the total number of PR sites, was defined from CART infusion to local relapse (LR) in the PR site identified on day +30. cRT was defined as comprehensive (compRT) - treated all PR PET-avid sites - or focal (focRT).

RESULTS

Followingday +30 PET scan, 45 PR patients were observed and 15 received cRT. Only one patient received consolidative systemic therapy and belonged to the cRT group. Prior to CART, bridging RT was given to 13 patients (9 in observation group and 4 in cRT group). There were no significant differences in the pre-CART and day +30 baseline characteristics, including the median size and SUVmax of the PR sites, between the two groups. However, the median number of PR sites on day +30 was higher in the cRT group (2 [range 1-3] vs 1 [range 1-3], p = 0.003). The median equivalent 2 Gy dose was 39.1 (Interquartile range 36.8-41) Gy, and the most common cRT regimen was 37.5 Gy in 15 fractions. The median follow-up was 21 months. Among the observed patients, 15 (33%) achieved spontaneous CR, and 27 (60%) experienced disease progression with all relapses involving the initial PR sites. Among patients who received cRT, 10 (67%) achieved CR, and 3 (20%) had disease progression with no relapses in the radiated PR sites. None of the 10 cRT patients achieving CR relapsed or required subsequent therapies. The 2-year PFS was 80% and 37% (p = 0.012) and the 2-year OS was 78% and 43% (p = 0.12) in the cRT and observation groups, respectively. Patients consolidated with compRT (n = 12) had superior 2-year PFS (92% vs 37%, p = 0.003) and 2-year OS (86% vs 43%, p = 0.048) compared to observed or focRT patients (n = 48). There were no grade 3+ RT-related toxicities. A total of 90 PR sites were identified; 64 were observed and 26 received cRT. Fourteen (22%) observed PR sites achieved spontaneous sustained CR and 42 (66%) experienced LR. Twenty-four (92%) PR sites consolidated with cRT achieved sustained CR and none experienced LR. The 2-year LRFS was 100% in the cRT sites and 31% in the observed sites (p<0.001).

CONCLUSION

NHL patients who achieve PR by PET to CART are at high risk of local progression. cRT for residual PET-avid disease on day +30 post-CART appears to alter the pattern of relapse and improve LRFS and PFS.

Predictors of Local Control with Palliative Radiotherapy for Multiple Myeloma

PURPOSE/OBJECTIVE(S)

Palliative radiotherapy (RT) is employed for patients with multiple myeloma to improve or prevent symptoms. However, the optimal dose fractionation is not well defined. The role of cytogenetics in informing RT warrants further study. We performed an institutional analysis of patients with multiple myeloma receiving palliative RT and assessed factors associated with local progression, with a focus on dose fractionation and cytogenetic abnormalities.

MATERIALS/METHODS

We queried a prospectively maintained, departmental database for consecutive patients who received palliative RT for multiple myeloma at our institution from 2015 to 2020. Double- and triple-hit were defined as the presence of two and three high-risk cytogenetic abnormalities. RT dose fractionation data were extracted from the database. Follow-up imaging was used to evaluate for progression.

RESULTS

A total of 239 patients with 362 treated lesions were included. Twenty-five patients (10.4%) with 39 lesions had double-hit cytogenetics, and 4 patients (1.7%) with 7 lesions were triple-hit. Patients had the following number of lesions treated with RT: 1 (156, 65.3%), 2 (53, 22.2%), 3 (17, 7.1%), or >3 (13, 5.4%). The most commonly targeted sites were spine (125, 34.5%), abdomen/pelvis (67, 18.5%), and lower extremity (53, 14.6%). Most lesions received doses of 20 Gy/5 fx (132, 36.5%), 8 Gy/1 fx (93, 25.7%), or 30 Gy/10 fx (48, 13.3%). RT equivalent dose in 2 Gray fractions (EQD2) was <2000 cGy for 126 lesions (34.8%) and ≥2000 cGy for 236 lesions (65.2%). At a median follow-up of 4.3 years, the risk of local progression on a per lesion basis at 1 and 4 years was 7.8% (95% CI: 5.5-11.1) and 13.4% (10.3-17.5), respectively. No cytogenetic abnormalities were correlated with local progression. Factors significant on univariate analysis included female sex [hazard ratio (HR): 1.94 (1.02-3.71), p = .045], LDH at diagnosis [HR per 10 units/liter: 1.04 (1.09-1.08), p = .016], and number of treated lesions [HR per lesion: 1.38 (1.02-1.89), p = .039]. These three covariates were included on multivariable analysis, and the only covariate to approach significance was number of treated lesions [HR for >3 versus 1: 2.43 (0.88-6.74), p = .059]. In the overall cohort, EQD2 did not impact risk of progression. Among those with >3 treated lesions, EQD2 ≥2000 cGy was associated with a significantly lower risk of progression [HR: 0.05 (0.01-0.23), p<.001]. Double- and triple-hit status were not correlated with progression. Median overall survival in all patients was 4.1 years versus 1.5 and 0.6 years in those with double- and triple-hit disease, respectively.

CONCLUSION

In this large, institutional study of patients with multiple myeloma, palliative RT achieves durable long-term local control. Patients with high disease burden may be at increased risk of progression at treated sites. This group may benefit from an EQD ≥2000 cGy. Cytogenetics, including double- and triple-hit status, do not appear to influence RT response.

Impact of Prostate Cancer Treatment with Low Dose Rate Brachytherapy on Testosterone: A Retrospective Analysis

PURPOSE/OBJECTIVE(S)

Decrease in serum testosterone counts have been reported in the literature following external beam radiotherapy (EBRT), with a suggested association to low dose irradiation of the testes occurring with historical and modern external techniques. Low dose rate (LDR) brachytherapy has been described as exposing the testes to between 2 and 19 cGy compared with 196-220 cGy with EBRT. This decrease in excess dose is hypothesized to spare post-treatment testosterone decrease and subsequent change in patient-perceived quality of life. Here, we retrospectively evaluate LDR-treated prostate cancer patient testosterone change in a single-institution patient cohort.

MATERIALS/METHODS

Patients with prostate cancer who had previously received LDR brachytherapy were identified, and patients with prior baseline total testosterone lab values as well as a lab value within one year post-treatment were identified. Patients receiving concurrent androgen deprivation therapy or EBRT were excluded. The closest baseline values prior to and after LDR treatment were used for before/after comparison. Samples were compared using the paired t-test.

RESULTS

A total of 1,463 patients receiving LDR were identified with data available for analysis between 1998 and 2023; of these, 139 patients met the above criteria for analysis. Mean age was 66 (median 67; range: 47 - 79). 5 patients received 110 Gy, 2 received 120 Gy, and the remainder 145 Gy, all conducted with I-125. Total mCi delivered ranged from 20.3 mCi to 56.7 mCi (median 37.6 mCi). Approximately 57% were GS6, 42% G7, and < 1% G8. Approximately 80% of patients had T1c disease, with 19% T2 and < 1% T3a. All patients were cN0M0. Mean pre- and post-treatment testosterone were 385.5 ng/dL and 382.9 (SD: 170.9, 150.9; mean difference 2.65 [95% CI: -15.6, 20.9]), respectively, with no statistical change noted (p = 0.774).

CONCLUSION

Testosterone levels have been reported to drop following definitive EBRT owing to excess dose delivery to the testes. On review of our institutional experience in definitive LDR brachytherapy for patients treated without ADT administration, no change in testosterone levels were noted.

Assessment of Minimum Dose as a Strong Predictor of Local Failure after Spine SBRT

PURPOSE/OBJECTIVE(S)

Stereotactic body radiation therapy (SBRT) has demonstrated robust clinical benefits in carefully selected patients, improving local control and even overall survival (OS). Even so, a wide range of dose-fractionation schemes are used in clinical practice. We seek to assess a large database to determine clinical and dosimetric predictors of local failure after spine SBRT.

MATERIALS/METHODS

From a large institutional database, spine SBRT treatments with subsequent imaging follow-up to assess local control were identified. Patients were treated with a simultaneous integrated boost technique using 1 or 3 fractions, generally delivering 20-24 Gy in 1 fraction to the high dose volume and 16 Gy to the low dose volume (or 30-36 Gy and 24 Gy for 3 fraction treatments). Exclusions included: lack of imaging follow-up, proton therapy, and benign primary histologies. Statistical analyses included Cox proportional hazards analyses and the robust log-rank statistic for cut-point analysis. The cumulative incidence of local failure with death as a competing risk was considered as the primary endpoint.

RESULTS

A total of 522 eligible spine SBRT treatments (68% single fraction) were identified in 377 unique patients. Patients had a median OS of 43.7 months (95% confidence interval: 34.3-54.4). The cumulative incidence of local failure was 19.3% (15.3-23.2) at 1 year and 25.6% (21.1-29.9) at 2 years. Univariate analysis identified that the minimum dose (normalized for the prescription dose) was a strong predictor of local failure (p = 0.0093). Among patients treated with a single fraction, statistical significance was maintained (p = 0.024). No other dosimetric factors were predictive of local failure. In a cut point analysis, the log-rank statistic was maximized at 15.8 Gy minimum dose for single-fraction treatment (HR = 0.51, 95% CI: 0.34 - 0.75, p = 0.0009). Cumulative incidence of local failure was 15.1% (9.8-20.2) vs. 24.7% (17.2-31.5) at 1 year using this cut-off. Comparable local control was demonstrated with a minimum dose of 14 Gy (HR = 0.57, 95%: 0.37 - 0.87, p = 0.009), with reduced local control with lower minimum doses. Among a range of clinical factors assessed, only epidural and soft tissue involvement were predictive of local failure (HR = 1.80 and 1.98, respectively). Multivariable analyses incorporating soft tissue involvement, epidural extension, and multilevel disease confirmed the 15.8 Gy cutoff for single fraction cases (HR = 0.58, 95% CI: 0.38-0.88, p = 0.011).

CONCLUSION

Spine SBRT offers favorable local control using a range of dose-fractionation schemes; however, minimum dose has a strong association with local control, unlike any other dosimetric factors tested. Furthermore, statistical significance was maintained even when considering epidural extension and potential limitations from dose to the spinal cord. Our data suggests that the minimum dose should be prioritized during treatment planning, ideally to at least 14 - 15.8 Gy for single fraction.

Multi-Institutional Analysis of Metastasis Directed Therapy with or without Androgen Deprivation Therapy in Oligometastatic Castration Sensitive Prostate Cancer

PURPOSE/OBJECTIVE(S)

Several prospective trials in oligometastatic castration sensitive prostate cancer (omCSPC) have shown metastasis-directed therapy (MDT) can delay time to progression and initiation of androgen deprivation therapy (ADT) compared to observation. However, the optimal integration of ADT with MDT remains unclear. Here we report a multi-national, multi-institutional retrospective cohort of omCSPC treated with MDT to characterize the long-term outcomes of patients treated with MDT alone or in combination with ADT.

MATERIALS/METHODS

Patients with a controlled primary site and omCSPC (defined as ≤ 5 lesions on conventional imaging) treated with MDT with or without concurrent ADT and with at least 36 months follow-up were retrospectively screened across 13 institutions. The primary endpoints included biochemical progression free survival (bPFS) and radiographic progression free survival (rPFS) calculated using Kaplan-Meier method and stratified by treatment group (MDT alone vs MDT + ADT). Multivariable Cox regression was performed adjusted for variables found to be prognostic on univariate analysis.

RESULTS

Among 414 patients screened, a total of 263 patients treated between 2003 and 2018 met inclusion criteria and included. Of these, 105 received MDT alone and 158 received MDT+ADT, with median follow-up of 49.5 and 54.5 months, respectively. The majority were metachronous (90%) and had bone lesions (60%). Median ADT duration was 21.3 months (IQR 12.0- 31.9). Patients who received ADT vs. no ADT had poorer prognostic features including 23% vs. 1% synchronous (p<0.001), and 55% vs 40% Gleason 8-10 (p = 0.012). ADT use was associated with a better 5-year bPFS 24% vs 11% (p<0.0001) and rPFS 41% vs 29% (p<0.001). On multivariable Cox regression adjusting for post-MDT PSA nadir and salvage therapy, ADT use maintained significance for both bPFS (HR 0.51 (0.36, 0.71), p<0.001) and rPFS (HR 0.67, 95% CI 0.46-0.96, p = 0.03).

CONCLUSION

Long-term outcomes with MDT alone suggest a small proportion of patients experience sustained disease control. The addition of ADT appears to improve rPFS, however prospective studies are needed in order to allow for personalization of care in patients with omCSPC.

Sensitivity of the PROMIS-10 for Capturing Radiation-Related Quality of Life Changes

PURPOSE/OBJECTIVE(S)

Patient reported outcomes (PROs) are becoming more common when assessing the effects of radiotherapy (RT). The aim of this study was to assess the sensitivity of the Mental and Physical domains of the Patient-Reported Outcomes Measurement Information System 10 (PROMIS-10) to radiotherapy and determine what predictors were associated with change in quality of life.

MATERIALS/METHODS

Patients, regardless of cancer type, were enrolled on a multi-site prospective registry. Inclusion criteria included curative radiotherapy and completion of the PROMIS-10 prior to treatment (Baseline) and at End of Treatment (EOT). To assess the strongest predictors of change in the T score of mental and physical health, we included 14 demographic characteristics and treatment variables in a multivariable stepwise regression.

RESULTS

A total of 7,586 patients were eligible for the analysis. The median age was 65 (range 18-94), 54% were males, and 94% were white. A majority received photons (62.5%) and the others received protons (37.5%) with an average dose of 52.3 Gy (range 20-80 Gy) over an average of 22.6 fractions (range 1-66). Patient disease sites were sub-grouped into 12 categories: Breast (25.5%), GU (23.0%), H&N (11.1%), CNS (8.5%), Pancreas-Biliary (6.7%), Thoracic (5.7%), Soft Tissue/Bone (5.0%), Esophagus-Gastric (4.7%), Colorectal-Anus (4.4%), Heme/Lymph (2.6%), GYN (1.8%), and Skin/Melanoma (1.0%). For both outcomes, the model selected disease group as an important predictor and it explained the most variance in the outcome compared to the rest of the predictors. When probing the effect of disease group, H&N, Esophagus-Gastric, Skin/Melanoma, and Colorectal-Anus had the largest mean decrease in quality of life for both domains. For mental health, the model also selected radiation type. Patients treated with protons indicated a bigger decrease in mental health compared to patients treated with photons (b = 0.43, 95% CI: -0.01, 0.69). For physical health, the model selected total fractions, ethnicity, and T stage. As number of fractions increased, the physical health change scores became more negative, on average (b = -0.03, 95% CI: -0.05, -0.01). Hispanic/Latino patients indicated a smaller decrease in physical health compared to White (b = -1.50, 95% CI: -2.60, -0.40) and Unknown ethnicity patients (b = -1.82, 95% CI: -3.36, -0.27). Finally, patients with a T stage of 3 or greater indicated a smaller decrease in physical health than patients with a T stage less than 3 (b = 0.76, 95% CI: 0.35, 1.16).

CONCLUSION

The PROMIS-10 did not capture significant change for patients undergoing curative radiotherapy except for patients with Head & Neck, Esophagus-Gastric, Skin, and Colorectal-Anus cancer. Further analyses should explore which patients experience the greatest change in quality of life within disease group.

Long-Term Patient-Reported Bowel and Urinary Quality of Life in Patients Treated with Intensity-Modulated Radiotherapy and Intensity-Modulated Proton Therapy for Localized Prostate Cancer

PURPOSE/OBJECTIVE(S)

To assess long-term differences in patient-reported outcomes in bowel and urinary domains between intensity-modulated radiotherapy (IMRT) and intensity-modulated proton therapy (IMPT) for prostate cancer.

MATERIALS/METHODS

Bowel function (BF), urinary irritative/obstructive symptoms (UO), and urinary incontinence (UI) domains of EPIC-26 were collected in patients with T1-T2 prostate cancer receiving IMRT or IMPT at a tertiary cancer center (2015-2018). Mean changes in domain scores were analyzed from pretreatment to 24 months post-radiotherapy for each modality. A clinically meaningful change was defined as a score change >50% of the standard deviation of a baseline score.

RESULTS

A total of 82 patients treated with IMRT (52.2%) and 56 patients treated with IMPT (53.3%) completed the questionnaire at baseline and 24 months post-RT. There were no baseline differences in domain scores between treatment modalities. At 24 months post-radiotherapy, there was significant and clinically meaningful decline of BF mean score in the IMRT cohort (-4.52 [range -50, 29.17], p = 0.003), whereas the decline in BF score did not reach statistical significance (-1.88 [range -37.5,50], p = 0.046) when accounting for the Bonferroni adjustment nor clinical relevance in the IMPT cohort. A higher proportion of patients treated with IMRT had a clinically relevant reduction in BF when compared with IMPT (47.37% vs 25.93%, p = 0.017). The mean changes in UI and UO scores of the IMRT and IMPT cohorts were neither statically significant nor clinically relevant.

CONCLUSION

IMPT has less decrement in BF than IMRT at 24 months post-RT, while there was no differential effect on UO and UI.

Phase II Evaluation of Stereotactic Ablative Radiotherapy (SABR) and Immunity in 11C-Choline-PET/CT-Identified Oligometastatic Castration-Resistant Prostate Cancer

PURPOSE

Outcomes for resistant metastatic castration-resistant prostate cancer (CRPC) are poor. Stereotactic ablative radiotherapy (SABR) induces antitumor immunity in clinical and preclinical studies, but immunologic biomarkers are lacking.

PATIENTS AND METHODS

Eighty-nine patients with oligometastatic CRPC were identified by ¹¹C-Choline-PET (Choline-PET) from August 2016 to December 2019 and treated with SABR. Prespecified coprimary endpoints were 2-year overall survival (OS) and PSA progression. Secondary endpoints included 2-year SABR-treated local failure and 6-month adverse events. Correlative studies included peripheral blood T-cell subpopulations before and after SABR.

RESULTS

128 lesions in 89 patients were included in this analysis. Median OS was 29.3 months, and 1- and 2-year OS were 96% and 80%, respectively. PSA PFS was 40% at 1 year and 21% at 2 years. Local PFS was 84.4% and 75.3% at 1 and 2 years, respectively, and no grade ≥3 AEs were observed. Baseline high levels of tumor-reactive T cells (T_TR; CD8⁺CD11a^high) predicted superior local, PSA, and distant PFS. Baseline high levels of effector memory T cells (T_EM; CCR7^-CD45RA^-) were associated with improved PSA PFS. An increase in T_TR at day 14 from baseline was associated with superior OS.

CONCLUSIONS

This is the first comprehensive effector T-cell immunophenotype analysis in a phase II trial before and after SABR in CRPC. Results are favorable and support the incorporation of immune-based markers in the design of future randomized trials in patients with oligometastatic CRPC treated with SABR.

Design and modification of EGF4KDEL 7Mut, a novel bispecific ligand-directed toxin, with decreased immunogenicity and potent anti-mesothelioma activity

BACKGROUND

Potency, immunogenicity, and toxicity are three problems that limit the use of targeted toxins in solid tumour therapy.

METHODS

To address potency, we used genetic engineering to develop a novel bispecific ligand-directed toxin (BLT) called EGF4KDEL, a novel recombinant anti-mesothelioma agent created by linking human epidermal growth factor (EGF) and interleukin-4 (IL-4) to truncated pseudomonas exotoxin (PE38) on the same single-chain molecule. Immunogenicity was reduced by mutating seven immunodominant B-cell epitopes on the PE38 molecule to create a new agent, EGF4KDEL 7Mut.

RESULTS

In vitro, bispecific EGF4KDEL showed superior anti-mesothelioma activity compared with its monospecific counterparts. Toxicity in mice was diminished by having both ligands on the same molecule, allowing administration of a 10-fold greater dose of BLT than a mixture of monomeric IL4KDEL and EGFKDEL. EGF4KDEL 7Mut, retained all of its functional activity and induced about 87% fewer anti-toxin antibodies than mice given the parental, non-mutated form. In vivo, intraperitoneal (IP) injection of the BLT showed significant (P<0.01) and impressive effects against two aggressive, malignant IP mesothelioma models when treatment was begun 14-16 days post tumour innoculation.

CONCLUSION

These data show that EGF4KDEL 7Mut is a promising new anti-mesothelioma agent that was developed to specifically address the obstacles facing clinical utility of targeted toxins.