Predicting the Effect of Proton Beam Therapy Technology on Pulmonary Toxicities for Patients With Locally Advanced Lung Cancer Enrolled in the Proton Collaborative Group Prospective Clinical Trial

PURPOSE

This study aimed to predict the probability of grade ≥2 pneumonitis or dyspnea within 12 months of receiving conventionally fractionated or mildly hypofractionated proton beam therapy for locally advanced lung cancer using machine learning.

METHODS AND MATERIALS

Demographic and treatment characteristics were analyzed for 965 consecutive patients treated for lung cancer with conventionally fractionated or mildly hypofractionated (2.2-3 Gy/fraction) proton beam therapy across 12 institutions. Three machine learning models (gradient boosting, additive tree, and logistic regression with lasso regularization) were implemented to predict Common Terminology Criteria for Adverse Events version 4 grade ≥2 pulmonary toxicities using double 10-fold cross-validation for parameter hyper-tuning without leak of information. Balanced accuracy and area under the curve were calculated, and 95% confidence intervals were obtained using bootstrap sampling.

RESULTS

The median age of the patients was 70 years (range, 20-97), and they had predominantly stage IIIA or IIIB disease. They received a median dose of 60 Gy in 2 Gy/fraction, and 46.4% received concurrent chemotherapy. In total, 250 (25.9%) had grade ≥2 pulmonary toxicity. The probability of pulmonary toxicity was 0.08 for patients treated with pencil beam scanning and 0.34 for those treated with other techniques (P = 8.97e-13). Use of abdominal compression and breath hold were highly significant predictors of less toxicity (P = 2.88e-08). Higher total radiation delivered dose (P = .0182) and higher average dose to the ipsilateral lung (P = .0035) increased the likelihood of pulmonary toxicities. The gradient boosting model performed the best of the models tested, and when demographic and dosimetric features were combined, the area under the curve and balanced accuracy were 0.75 ± 0.02 and 0.67 ± 0.02, respectively. After analyzing performance versus the number of data points used for training, we observed that accuracy was limited by the number of observations.

CONCLUSIONS

In the largest analysis of prospectively enrolled patients with lung cancer assessing pulmonary toxicities from proton therapy to date, advanced machine learning methods revealed that pencil beam scanning, abdominal compression, and lower normal lung doses can lead to significantly lower probability of developing grade ≥2 pneumonitis or dyspnea.

Associations Between Mean Lung Dose and Prevalence of Radiation Pneumonitis in Elderly Lung Cancer Patients

BACKGROUND/AIM

Pneumonitis is a serious radiotherapy complication. This study, which is a prerequisite for a prospective trial, aimed to identify the prevalence of pneumonitis and risk factors in elderly patients with lung cancer.

PATIENTS AND METHODS

Ninety-eight lung cancer patients aged ≥65 years were included. Seventeen factors were investigated regarding grade ≥2 pneumonitis at 24 weeks following radiotherapy.

RESULTS

The prevalence of grade ≥2 pneumonitis at 24 weeks was 27.3%. On univariate analysis, a significant association was observed for mean (ipsilateral) lung dose (MLD; ≤13.0 vs. 13.1-20.0 vs. >20.0 Gy; 0% vs. 24.9% vs. 48.7%). Results were significant also for ≤13.0 vs. >13.0 Gy (0% vs. 37.1%) or ≤20.0 vs. >20.0 Gy (13.4% vs. 48.7%). MLD achieved significance on multivariate analysis.

CONCLUSION

Elderly patients receiving MLDs >13.0 Gy, particularly >20.0 Gy, have a high risk of grade ≥2 pneumonitis. These results are important for designing a prospective trial.

The Role of Radiotherapy for Meningeal Melanocytomas - A 20 Year Update

BACKGROUND/AIM

Meningeal melanocytomas are rare tumors of the central nervous system and optimal treatment needs further clarification. This study compared subtotal resection (STR), STR plus radiation therapy (RT), gross total resection (GTR), and GTR+RT to better define the role of postoperative RT.

PATIENTS AND METHODS

All cases reported in the literature were reviewed. Patients (n=184) with complete data were analyzed for local control (LC) and overall survival (OS).

RESULTS

On univariate analysis, GTR (vs. STR) was associated with improved LC (p=0.016). When comparing the treatment regimens, best and worst results were found after GTR+RT and STR alone, respectively (p<0.001). On univariate analysis, GTR resulted in better OS than STR (p=0.041). Moreover, the treatment regimen had a significant impact on OS (p=0.049). On multivariate analyses of LC and OS, extent of resection and treatment regimen were found to be significant factors. After STR, RT significantly improved LC but not OS. After GTR, RT did not significantly improve LC or OS.

CONCLUSION

GTR was significantly superior to STR regarding LC and OS. STR+RT resulted in significantly better LC when compared to STR alone.

NRG Oncology and PTCOG Patterns of Practice Survey and Consensus Recommendations on Pencil-Beam Scanning Proton Stereotactic Body Radiation Therapy and Hypofractionated Radiation Therapy for Thoracic Malignancies

Stereotactic body radiation therapy (SBRT) and hypofractionation using pencil-beam scanning (PBS) proton therapy (PBSPT) is an attractive option for thoracic malignancies. Combining the advantages of target coverage conformity and critical organ sparing from both PBSPT and SBRT, this new delivery technique has great potential to improve the therapeutic ratio, particularly for tumors near critical organs. Safe and effective implementation of PBSPT SBRT/hypofractionation to treat thoracic malignancies is more challenging than the conventionally fractionated PBSPT because of concerns of amplified uncertainties at the larger dose per fraction. The NRG Oncology and Particle Therapy Cooperative Group Thoracic Subcommittee surveyed proton centers in the United States to identify practice patterns of thoracic PBSPT SBRT/hypofractionation. From these patterns, we present recommendations for future technical development of proton SBRT/hypofractionation for thoracic treatment. Among other points, the recommendations highlight the need for volumetric image guidance and multiple computed tomography-based robust optimization and robustness tools to minimize further the effect of uncertainties associated with respiratory motion. Advances in direct motion analysis techniques are urgently needed to supplement current motion management techniques.

Beam mask and sliding window-facilitated deep learning-based accurate and efficient dose prediction for pencil beam scanning proton therapy

BACKGROUND

Accurate and efficient dose calculation is essential for on-line adaptive planning in proton therapy. Deep learning (DL) has shown promising dose prediction results in photon therapy. However, there is a scarcity of DL-based dose prediction methods specifically designed for proton therapy. Successful dose prediction method for proton therapy should account for more challenging dose prediction problems in pencil beam scanning proton therapy (PBSPT) due to its sensitivity to heterogeneities.

PURPOSE

To develop a DL-based PBSPT dose prediction workflow with high accuracy and balanced complexity to support on-line adaptive proton therapy clinical decision and subsequent replanning.

METHODS

PBSPT plans of 103 prostate cancer patients (93 for training and the other 10 for independent testing) and 83 lung cancer patients (73 for training and the other 10 for independent testing) previously treated at our institution were included in the study, each with computed tomography scans (CTs), structure sets, and plan doses calculated by the in-house developed Monte-Carlo dose engine (considered as the ground truth in the model training and testing). For the ablation study, we designed three experiments corresponding to the following three methods: (1) Experiment 1, the conventional region of interest (ROI) (composed of targets and organs-at-risk [OARs]) method. (2) Experiment 2, the beam mask (generated by raytracing of proton beams) method to improve proton dose prediction. (3) Experiment 3, the sliding window method for the model to focus on local details to further improve proton dose prediction. A fully connected 3D-Unet was adopted as the backbone. Dose volume histogram (DVH) indices, 3D Gamma passing rates with a criterion of 3%/3 mm/10%, and dice coefficients for the structures enclosed by the iso-dose lines between the predicted and the ground truth doses were used as the evaluation metrics. The calculation time for each proton dose prediction was recorded to evaluate the method's efficiency.

RESULTS

Compared to the conventional ROI method, the beam mask method improved the agreement of DVH indices for both targets and OARs and the sliding window method further improved the agreement of the DVH indices (for lung cancer, CTV D98 absolute deviation: 0.74 ± 0.18 vs. 0.57 ± 0.21 vs. 0.54 ± 0.15 Gy[RBE], ROI vs. beam mask vs. sliding window methods, respectively). For the 3D Gamma passing rates in the target, OARs, and BODY (outside target and OARs), the beam mask method improved the passing rates in these regions and the sliding window method further improved them (for prostate cancer, targets: 96.93% ± 0.53% vs. 98.88% ± 0.49% vs. 99.97% ± 0.07%, BODY: 86.88% ± 0.74% vs. 93.21% ± 0.56% vs. 95.17% ± 0.59%). A similar trend was also observed for the dice coefficients. This trend was especially remarkable for relatively low prescription isodose lines (for lung cancer, 10% isodose line dice: 0.871 ± 0.027 vs. 0.911 ± 0.023 vs. 0.927 ± 0.017). The dose predictions for all the testing cases were completed within 0.25 s.

CONCLUSIONS

An accurate and efficient deep learning-augmented proton dose prediction framework has been developed for PBSPT, which can predict accurate dose distributions not only inside but also outside ROI efficiently. The framework can potentially further reduce the initial planning and adaptive replanning workload in PBSPT.

Proton Pencil-Beam Scanning Stereotactic Body Radiation Therapy and Hypofractionated Radiation Therapy for Thoracic Malignancies: Patterns of Practice Survey and Recommendations for Future Development from NRG Oncology and PTCOG

Stereotactic body radiation therapy (SBRT) and hypofractionation using pencil-beam scanning (PBS) proton therapy (PBSPT) is an attractive option for thoracic malignancies. Combining the advantages of target coverage conformity and critical organ sparing from both PBSPT and SBRT, this new delivery technique has great potential to improve the therapeutic ratio, particularly for tumors near critical organs. Safe and effective implementation of PBSPT SBRT/hypofractionation to treat thoracic malignancies is more challenging than the conventionally-fractionated PBSPT due to concerns of amplified uncertainties at the larger dose per fraction. NRG Oncology and Particle Therapy Cooperative Group (PTCOG) Thoracic Subcommittee surveyed US proton centers to identify practice patterns of thoracic PBSPT SBRT/hypofractionation. From these patterns, we present recommendations for future technical development of proton SBRT/hypofractionation for thoracic treatment. Amongst other points, the recommendations highlight the need for volumetric image guidance and multiple CT-based robust optimization and robustness tools to minimize further the impact of uncertainties associated with respiratory motion. Advances in direct motion analysis techniques are urgently needed to supplement current motion management techniques.

Distress Scores in Elderly Cancer Patients During Radiotherapy

BACKGROUND/AIM

When assigned to radiotherapy (RT), elderly patients may experience distress. We investigated distress during RT and potential risk factors in these patients.

PATIENTS AND METHODS

Six-hundred-and-nineteen patients completed pre-RT and post-RT distress thermometers. Seven characteristics were investigated including age, sex, Karnofsky performance score (KPS), grouped KPS, tumor type, intent of RT, and previous RT. Additional analyses were performed in 358 patients with pre-RT scores ≤5.

RESULTS

Mean change of distress was -0.5 (±2.7) points and associated with KPS (p=0.005) and grouped KPS (p<0.001). Male sex (p=0.035), KPS 90-100 (p=0.001), and curative intent (p=0.037) were associated with increased distress on univariable analyses, and KPS 90-100 (odds ratio=1.92, p=0.004) on multivariable analysis. In patients with baseline scores ≤5, mean change was +0.5 (±2.5) points and associated with KPS (p=0.040) and grouped KPS (p=0.025).

CONCLUSION

Psychological assistance should be considered for all patients including those with baseline scores ≤5 and KPS 90-100. Patients with risk factors for increased distress would especially benefit.

Chemoimmunotherapy in patients with extensive-stage small cell lung cancer and a poor performance status

BACKGROUND

Immune checkpoint inhibitor combined with platinum-etoposide is the standard first-line therapy for patients with extensive-stage small cell lung cancer (ES-SCLC). The phase 3 clinical trials that led to the approval of chemoimmunotherapy in ES-SCLC excluded patients who had an Eastern Cooperative Group (ECOG) performance status (PS) of 2-3. Therefore, data on the efficacy of chemoimmunotherapy in patients with an ECOG PS of 2-3 are limited.

METHODS

A retrospective analysis was performed on patients diagnosed with ES-SCLC who received chemoimmunotherapy (atezolizumab or durvalumab) within the Mayo Clinic Health System between January 2016 and January 2021. The objective of this study was to compare the overall survival (OS), progression-free survival (PFS), and best clinical response to therapy in patients with an ECOG PS of 0-1 vs. patients with an ECOG PS of 2-3 who received chemoimmunotherapy for newly diagnosed ES-SCLC.

RESULTS

In total, 82 patients were included in the study. The mean ± standard deviation age was 68.1 ± 8.3 years. Of these, 56 patients were identified with an ECOG PS of 0-1, and 26 patients were identified with an ECOG PS of 2-3. The median PFS was similar regardless of ECOG PS (5.8 months [95% CI, 4.3-6.0 months] in the ECOG PS 0-1 group vs. 4.1 months [95% CI, 3.8-6.9 months] in the ECOG PS 2-3; p = .2994). The median OS was also similar regardless of ECOG PS (10.6 months [95% CI, 8.4-13.4 months] in the ECOG PS 0-1 group vs. 9.3 months [95% CI, 4.9-12.8 months]; p = .2718) in the ECOG PS 2-3 group.

CONCLUSIONS

The study results demonstrated no significant difference in PFS or OS among the ECOG PS 2-3 and ECOG PS 0-1 groups. Therefore, chemoimmunotherapy should be considered for patients who have ES-SCLC with an ECOG PS of 2-3.

Chemoimmunotherapy as the First-Line Treatment for Patients With Extensive-Stage Small-Cell Lung Cancer and an ECOG Performance Status 2 or 3

BACKGROUND

Studies demonstrated that chemoimmunotherapy prolongs progression-free survival (PFS) and overall survival (OS) in patients with extensive-stage small-cell lung cancer (ES-SCLC) and an Eastern Cooperative Oncology Group performance status (ECOG PS) 0 or 1. However, there is little data regarding chemoimmunotherapy in patients with ES-SCLC and an ECOG PS 2 or 3. This study aims to evaluate the benefits of chemoimmunotherapy compared to chemotherapy in the first-line treatment of patients with ES-SCLC and ECOG PS 2 or 3.

MATERIALS AND METHODS

This retrospective study analyzed 46 adults treated at Mayo Clinic between 2017 and 2020 with de novo ES-SCLC and an ECOG PS 2 or 3. Twenty patients received platinum-etoposide and 26 patients received platinum-etoposide and atezolizumab. Progression-free survival (PFS) and Overall survival (OS) were calculated using Kaplan-Meier methods.

RESULTS

PFS was longer in the chemoimmunotherapy group compared to the chemotherapy group, 4.1 months (95% confidence interval [CI]: 3.8-6.9) vs. 3.2 months (95% CI: 0.6-4.8), respectively; P = 0.0491. However, there was no statistically significant difference in the OS between the chemoimmunotherapy and chemotherapy group, 9.3 months (95% CI: : 4.9-12.8) vs. 7.6 months (95% CI: 0.6-11.9), respectively; P = .21.

CONCLUSION

Chemoimmunotherapy prolongs PFS compared to chemotherapy in patients with newly diagnosed ES-SCLC and an ECOG PS 2 or 3.  No OS difference was observed among the chemoimmunotherapy and chemotherapy groups; nevertheless, this may be attributed due to the small sample size of the study.

Development of Distress During a Radiotherapy Course in Patients Irradiated for Breast Cancer

BACKGROUND/AIM

Breast cancer patients receiving radiation therapy (RT) may experience considerable distress. We investigated the course of distress during an RT-course for breast cancer.

PATIENTS AND METHODS

Three-hundred-and-thirty breast cancer patients completed Distress Thermometers before and directly after RT. Distress was evaluated in the entire cohort and different groups of age, sex, Karnofsky performance score (KPS), intent of RT, and previous RT.

RESULTS

Mean change of distress scores was - 0.4 points, which was significantly associated with KPS. Decrease of distress was more pronounced in patients with KPS ≤80 or age <64 years. Deterioration (yes vs. no) was non-significantly associated with no previous RT. In patients with pre-RT distress scores ≤5 points, mean score increased by +0.5 points; no significant associations between characteristics and investigated endpoints were found.

CONCLUSION

Psychological assistance should be offered to all patients irradiated for breast cancer, particularly to those with risk factors, regardless of the pre-RT distress score.

Whole-breast Radiotherapy With Boost for Node-negative Breast Cancer: Conventional vs. Hypo-fractionation

BACKGROUND/AIM

Many breast cancer patients receive adjuvant radiotherapy. Tumor bed boost may reduce risk of local failure in high risk patients. We compared hypofractionated whole-breast irradiation (WBI) plus boost (HF+boost) and conventionally fractionated WBI plus boost (CF+boost).

PATIENTS AND METHODS

One-hundred-and-twenty-eight patients receiving HF-WBI (40 Gy in 15 fractions) plus boost (group A) were matched to 127 patients receiving CF-WBI (50.4 Gy in 28 fractions) plus boost (group B), utilizing 10 characteristics.

RESULTS

Grade ≥2 dermatitis rates were 16.4% in group A vs. 44.1% in group B (p<0.0001), and grade ≥2 pneumonitis rates were 1.6% vs. 2.4% (p=0.68). Four-year rates of local control, metastases-free survival, and overall survival were 100% vs. 99% (p=0.81), 98% vs. 100% (p=0.29), and 98% vs. 100% (p=0.17), respectively.

CONCLUSION

HF+boost was associated with significantly less grade ≥2 dermatitis with similar disease control and survival.

Deep-learning based fast and accurate 3D CT deformable image registration in lung cancer

BACKGROUND

Deformable Image Registration (DIR) is an essential technique required in many applications of radiation oncology. However, conventional DIR approaches typically take several minutes to register one pair of 3D CT images and the resulting deformable vector fields (DVFs) are only specific to the pair of images used, making it less appealing for clinical application.

PURPOSE

A deep-learning-based DIR method using CT images is proposed for lung cancer patients to address the common drawbacks of the conventional DIR approaches and in turn can accelerate the speed of related applications, such as contour propagation, dose deformation, adaptive radiotherapy (ART), etc. METHODS: A deep neural network based on VoxelMorph was developed to generate DVFs using CT images collected from 114 lung cancer patients. Two models were trained with the weighted mean absolute error (wMAE) loss and structural similarity index matrix (SSIM) loss (optional) (i.e., the MAE model and the M+S model). In total, 192 pairs of initial CT (iCT) and verification CT (vCT) were included as a training dataset and the other independent 10 pairs of CTs were included as a testing dataset. The vCTs usually were taken 2 weeks after the iCTs. The synthetic CTs (sCTs) were generated by warping the vCTs according to the DVFs generated by the pre-trained model. The image quality of the synthetic CTs was evaluated by measuring the similarity between the iCTs and the sCTs generated by the proposed methods and the conventional DIR approaches, respectively. Per-voxel absolute CT-number-difference volume histogram (CDVH) and MAE were used as the evaluation metrics. The time to generate the sCTs was also recorded and compared quantitatively. Contours were propagated using the derived DVFs and evaluated with SSIM. Forward dose calculations were done on the sCTs and the corresponding iCTs. Dose volume histograms (DVHs) were generated based on dose distributions on both iCTs and sCTs generated by two models, respectively. The clinically relevant DVH indices were derived for comparison. The resulted dose distributions were also compared using 3D Gamma analysis with thresholds of 3 mm/3%/10% and 2 mm/2%/10%, respectively.

RESULTS

The two models (wMAE and M+S) achieved a speed of 263.7±163 / 265.8±190 ms and a MAE of 13.15±3.8 / 17.52±5.8 HU for the testing dataset, respectively. The average SSIM scores of 0.987±0.006 and 0.988±0.004 were achieved by the two proposed models, respectively. For both models, CDVH of a typical patient showed that less than 5% of the voxels had a per-voxel absolute CT-number-difference larger than 55 HU. The dose distribution calculated based on a typical sCT showed differences of ≤2cGy[RBE] for clinical target volume (CTV) D95 and D5 , within ±0.06% for total lung V5 , ≤1.5cGy[RBE] for heart and esophagus Dmean , and ≤6cGy[RBE] for cord Dmax compared to the dose distribution calculated based on the iCT. The good average 3D Gamma passing rates (> 96% for 3 mm/3%/10% and > 94% for 2 mm/2%/10%, respectively) were also observed.

CONCLUSION

A deep neural network-based DIR approach was proposed and has been shown to be reasonably accurate and efficient to register the initial CTs and verification CTs in lung cancer.

Radiation Dermatitis and Pneumonitis in Patients Irradiated for Breast Cancer

BACKGROUND/AIM

Adjuvant radiotherapy (RT) for breast cancer can be associated with acute dermatitis (ARD) and pneumonitis (RP). Prevalence and risk factors were characterized.

PATIENTS AND METHODS

This study included 489 breast cancer patients receiving adjuvant RT with conventional fractionation (CF) ± sequential or simultaneous integrated boost, or hypo-fractionation ± sequential boost. RT-regimen and 15 characteristics were investigated for grade ≥2 ARD and RP.

RESULTS

Prevalence of grade ≥2 ARD and RP was 25.3% and 2.5%, respectively. On univariate analyses, ARD was significantly associated with CF and radiation boost (p<0.0001), age ≤60 years (p=0.008), Ki-67 ≥15% (p=0.012), and systemic treatment (p=0.002). On multivariate analysis, RT-regimen (p<0.0001) and age (p=0.009) were associated with ARD. Chronic inflammatory disease was significantly associated with RP on univariate (p=0.007) and multivariate (p=0.016) analyses.

CONCLUSION

Risk factors for grade ≥2 ARD and RP were determined that may help identify patients who require closer monitoring during and after RT.

Insurance Request and Approval Process for Proton Beam Therapy in Patients with Esophageal Cancer

PURPOSE/OBJECTIVE(S)

Randomized data suggests proton beam therapy (PBT) reduces the risk and severity of toxicities when compared to IMRT in the neoadjuvant or definitive setting for esophageal cancer. As a critical barrier to access to PBT, we investigate our institutional experience with the prior authorization (PA) process for patients (pts) with esophageal cancer.

MATERIALS/METHODS

One hundred and four (104) consecutive pts with esophageal cancer from 2016-2020 at one institution for whom PBT was recommended were analyzed. Data was collected from the customer relations management (CRM) database and electronic health record. Patient characteristics, tumor characteristics, treatment parameters, types of insurance, and clinical outcomes (OS, LF, DF) were recorded. Timepoints of the steps of the PA process included the PA team's initial inquiry, the initial decision, first through third appeals, and outcomes of each appeal (the third of which was regarded as the final decision). Rates of approval and successful appeal were calculated. Logistic and Cox regression models were used to evaluate whether insurance decisions were associated with clinical factors or clinical outcomes.

RESULTS

Approval rates by Medicare (n = 68) and private insurance (n = 36) were 100 and 42% on initial request, at a median (range) 0 and 3 (0-15) days from inquiry to determination, respectively. All 21 pts initially denied coverage appealed the decision. Overall, denial was overturned in 48% of pts (median [range] time, 14 [7-36] days from initial inquiry [FIQ]), i.e., PBT was eventually approved for them. The remaining pts proceeded with self-pay or photon therapy. Upon first appeal, 14 pts were denied (median [range] time, 7 [1-26] days FIQ). Upon second appeal, 6 pts were denied (median [range] time, 18 [7-34] days FIQ). Finally, upon third appeal, 2 pts were denied and 1 patient was approved (median [range] time, 2 [20-39] days). Medicare insurance (P < .01) and possessing secondary insurance (P = .02) were found to be associated with increased likelihood of initial approval. Notably, a trend was found between clinical trial enrollment and decreased likelihood of initial approval. Neither initial nor final insurance decisions were found to be associated with OS, LF, or DF.

CONCLUSION

Despite randomized data and policy efforts supporting the use of PBT in esophageal cancer, pts with private payers experience treatment delays and often eventual denial after appeal.

Oncologic Outcomes of Conventionally Fractionated, Hypofractionated, and Stereotactic Body Spot-Scanned Proton Radiation Therapy for Prostate Cancer: The Mayo Clinic Experience

PURPOSE/OBJECTIVE(S)

Spot/pencil beam scanned proton therapy is a relatively new technology with fundamental differences from double scattered or IMRT. We aimed to report the long-term oncologic outcomes of a contemporary prospective series of patients treated with spot-scanned proton therapy (SSPT).

MATERIALS/METHODS

An IRB-approved prospective registry identified patients with prostate cancer treated with proton therapy between January 2016 and December 2018. Descriptive statistics were calculated for all patients. Clinical, demographic, and treatment characteristics were gathered and analyzed. Kaplan-Meier curves were generated to estimate survival and recurrence rates. Outcomes assessed included 5-year overall survival (OS), 5-year local control (LC), biochemical failure (BF), regional and distant failures, and physician-reported adverse events (AEs). Biochemical failure was defined as rise in PSA ≥ 2.0 ng/mL above nadir PSA. Acute and chronic gastrointestinal (GI) and genitourinary (GU) grade 2+ and grade 3+ baseline-adjusted AEs were assigned using CTCAE v5.0. All failures were re-staged with PET C-11 or PSMA.

RESULTS

With a median follow up of 4.4 years (IQR 3.7 - 5), two hundred and eighty-six prostate cancer patients with a median age of 72 (IQR 67.5 - 77) were treated with spot-scanned proton radiation. The median Gleason grade group was 3 (IQR 2 - 4). The median pre-RT PSA was 6.9 ng/mL (IQR 4.3 - 10.5). Median T-stage was T1c. Nearly 64% of all patients were on androgen deprivation therapy at the time of initiating radiation treatment. The median total radiation dose was 79.2 Gy delivered over 44 fractions, 70 Gy over 28 fractions, and 38 Gy over 5 fractions for CF, HF, and SBRT regimens, respectively. The BF rate for all patients was 8.4%. The 5-year LC rates for CF, HF, and SBRT were 100% (95% CI: 100 - 100), 100% (95% CI: 100 - 100), and 97.3% (95% CI: 92.2 - 100), respectively (p = 0.07). Regional recurrences occurred in 12 (4.2%) patients: 8 (5.6%) treated with CF, 2 (2.1%) with HF, and 2 (4.3%) with SBRT (p = 0.62). Distant metastatic failures occurred in 12 patients (4.2%): 5 (3.5%) treated with CF, 7 (7.4%) with HF, and none with SBRT (0%) (p = 0.052). The 5-year OS for patients treated with CF, HF, and SBRT SSPT were 88.2% (95% CI: 81.8 - 95), 86.2% (95% CI: 77.6 - 95.6), and 97.2% (95% CI: 92 - 100), respectively (p = 0.1). Acute and chronic grade 2+ GI baseline-adjusted AEs occurred in 8 (2.8%) and 51 (17.8%) patients, respectively. Acute and chronic grade 3+ GI baseline-adjusted AEs occurred in 3 (1%) and 4 (1.4%) patients, respectively. Acute and chronic grade 2+ GU-related AEs were observed in 72 (25.2%) and 63 (22%) patients, respectively. Acute and chronic grade 3+ GU toxicity was observed in 3 (1%) and 6 (2.1%) patients, respectively.

CONCLUSION

Spot-scanned proton radiation therapy provides high local control rates and excellent oncologic outcomes across different fractionation schedules with low long-term AE rates.

A Survival Score for Patients Treated with Whole-Brain Radiotherapy plus Simultaneous Integrated Boost for Brain Metastases

PURPOSE/OBJECTIVE(S)

Different types of radiotherapy (RT) are used for brain metastases including whole-brain RT (WBRT) and local therapies (radiosurgery, fractionated stereotactic RT). WBRT plus simultaneous integrated boost (WBRT+SIB) is another treatment option that was reported to improve intracranial control and overall survival (OS) when compared to WBRT alone. This study aimed to create a score to identify patients who may not benefit from this approach due to poor OS.

MATERIALS/METHODS

In 128 patients treated with WBRT+SIB for brain metastases (2014-2021), year of RT, interval from tumor diagnosis to RT, WBRT+SIB regimen [(14 x (2.5 + 0.5) Gy vs. 18 x (2.0 + 0.5) Gy], pre-RT systemic treatment, age, gender, performance score, primary tumor type, N lesions, and extracranial metastases were retrospectively evaluated for OS. Univariate analyses (UVA) were performed with Kaplan-Meier method and log-rank test. Factors that showed significant (p<0.05), a strong trend (p<0.07) or a trend (p<0.14) in UVA were included in a Cox proportional hazards model (MVA). To create the appropriate OS score, three models were created, one including factors significant on MVA, a second including factors with p<0.07 on UVA, and a third one including factors with p<0.14 on UVA. For each factor, 6-month OS rates (%) were divided by 10 and resulting points were added for each patient. Based on patient scores, three prognostic groups were designed for each model. Positive predictive values (PPV) of correct prediction of death ≤6 and OS ≥6 months were calculated.

RESULTS

On UVA, KPS >80 (p<0.001) and ≤3 lesions (p = 0.006) were associated with OS, age ≤64 years (p = 0.061) showed a strong trend, and no extracranial metastases (p = 0.128) a trend. On MVA, KPS (HR: 0.40, 95% CI: 0.27-0.61, p<0.001) and N lesions (HR: 1.81, 95% CI: 1.23-2.65, p = 0.002) were significant; age (HR: 1.12, 05% CI: 0-76-1.66, p = 0.57) and extracranial metastases (HR: 1.19, 95% CI: 0.79-1.78, p = 0.40) were not significant. In Model 1 (including only KPS and N lesions), groups were 5, 6-8 and 9 points with 6-month OS rates of 15%, 38% and 57%, respectively. PPVs to predict death and OS were 85% and 57%, respectively. In Model 2 (KPS, N lesions, age), groups were 8, 9-12 and 13 points with 6-month OS rates of 17%, 33% and 75%, respectively. PPVs were 83% and 75%, respectively. In Model 3 (KPS, N lesions, age, extracranial metastases), groups were 11, 12-16 and 17 points with 6-month OS rates of 14%, 34% and 78%, respectively. PPVs were 86% and 78%, respectively.

CONCLUSION

All three models achieved high accuracy regarding prediction of death ≤6 months and can help identify patients who may not be ideal candidates for WBRT+SIB. For prediction of OS ≥6 months, Models 2 and 3 were superior. Since differences between Models 2 and 3 were marginal and correct identification of extracranial metastases (Model 3) may require extensive staging, Model 2 appears preferable.

Simultaneous vs. Sequential Boost for Adjuvant Breast Radiotherapy

BACKGROUND/AIM

During the last 10-15 years, alternative regimens for adjuvant radiotherapy (RT) of breast cancer have become more popular, including simultaneous integrated (SIB) instead of sequential boosts (SEB). We present long-term outcomes after conventional fractionation (CF) plus SIB vs. CF+SEB.

PATIENTS AND METHODS

Forty-eight patients receiving CF+SIB (treatment time=5.5 weeks) were matched to 72 patients (control group) receiving CF+SEB (6.5 weeks) considering twelve characteristics. Both groups were compared for radiation dermatitis, pneumonitis, local control (LC), metastases-free survival (MFS), cancer-specific survival (CSS), and overall survival (OS).

RESULTS

Rates of grade ≥2 dermatitis were 35.4% (CF+SIB) and 45.8% (CF+SEB), respectively (p=0.26), and rates of grade ≥2 pneumonitis 0% and 4.2%, respectively (p=0.27). Six-year LC, MFS, CSS, and OS rates were 100% vs. 93% (p=0.11), 97% vs. 100% (p=0.29), 100% vs. 100% (p=1.00), and 98% vs. 100% (p=0.23), respectively.

CONCLUSION

CF+SIB was similar to CF+SEB in terms of toxicities and outcomes but reduces total treatment time by one week.

Treatment of Thymoma and Thymic Carcinoma with Proton Beam Therapy: Outcomes from the Proton Collaborative Group Prospective Registry

PURPOSE/OBJECTIVE(S)

Given the generally long natural history of thymic malignancies, proton beam therapy (PBT) is advocated to minimize the risk of long-term toxicities to mediastinal organs. Adverse events (AE) and long-term clinical outcomes for this population have not been well-characterized.

MATERIALS/METHODS

The Proton Collaborative Group registry (NCT01255748), a multi-institutional prospective database of academic and community proton centers in the US, was queried for patients with thymomas and thymic carcinomas treated with PBT. Patients with recurrent/metastatic disease, non-thymic histology, received either prior or palliative radiotherapy (dose < 40 Gy RBE) were excluded. Overall survival (OS) and local control (LC) were estimated using Kaplan-Meier methods.

RESULTS

A total of 97 patients were identified in the PCG registry. After applying relevant exclusion criteria, 70 patients from 12 proton centers treated from 2011-2021 were included for analysis. Median follow-up length was 16 months. Median age was 58.5 years (IQR 46-63), and 60% were female. 81.4% had a diagnosis of thymoma, and 18.6% thymic carcinoma. 59 patients underwent surgical resection. 11 were treated with definitive PBT, of which 5 received concurrent chemotherapy. Median dose was 54 Gy RBE (range 41.4 - 70 Gy RBE), median number of fractions was 30 (range 21 - 38). 73.4% received pencil beam scanning and 23% uniform scanning PBT. Treatment was overall well-tolerated: a single patient developed grade 4 pneumonitis. Grade 3 AEs were seen in 3 patients - dyspnea, anorexia, and heart failure. Highest grade toxicity experienced was grade 2 for 47.1% and grade 1 for 42.9% of patients. 3-year overall survival (OS) was 82.6% for the entire cohort. 3-year OS was 94% for resected/adjuvant cohort and 35.6% in the non-surgical/definitive cohort. 3-year local control (LC) was 91.7% for the entire cohort. By surgery/margin status, 3-year LC was 96.8% in patients with close or negative margins (a single failure in a patient with close margins), whereas 3-year LC was 55.1% for patients with positive margins/unresectable disease.

CONCLUSION

Thymic malignancies treated with PBT appear to have favorable outcomes, especially in the adjuvant setting, in this cohort representing the largest series of such patients.

Radiation Necrosis following SRS or FSRT with Higher BED for Brain Metastases >20 mm

PURPOSE/OBJECTIVE(S)

In the RTOG 90-05 study, the maximum tolerated dose of single-fraction radiosurgery (SRS) for lesions 21-30 mm was 18 Gy (BED 45 Gy12). However, patients of the RTOG study were previously irradiated with median 60 Gy (brain tumors) or 30 Gy (brain metastasis). Thus, the max. tolerated BED for lesions not irradiated before may be >45 Gy12. This study investigated safety and efficacy of SRS or fractionated stereotactic radiotherapy (FSRT) with BED >49 Gy12 for radiotherapy-naive brain metastases >20 mm.

MATERIALS/METHODS

Data of 169 patients who received SRS or FSRT alone with BED >49 Gy12 for 1-4 brain metastases (2011-2022) were retrospectively analyzed. Thirty-two patients had lesions >20 mm (21-30 mm, n = 27; 21-40 mm, n = 4; >40 mm, n = 1). SRS was performed with 20 Gy (n = 9; 53.3 Gy12) or 19 Gy (n = 2; 49.1 Gy12), prescribed to the 60-80% isodose line (PTV = GTV). FSRT was Linac-based delivering 3 x 10 Gy (n = 3; 55 Gy12), 3 x 11 Gy (n = 4; 63.3 Gy12), 7 x 6 Gy (n = 1; 63 Gy12), 9 x 5 Gy (n = 1; 63.8 Gy12), 10 x 4 Gy (n = 11; 53.3 Gy12), or 12 x 4 Gy (n = 1; 64 Gy12), prescribed to the 80% isodose line (PTV = GTV+1-2 mm). SRS and FSRT were compared for grade ≥2 radiation necrosis (RN), local control (LC) and survival (OS). Fractionation [SRS (n = 89) vs FSRT (n = 48)] and lesion size (≤20 vs >20 mm) were studied in terms of RN rates. Kaplan-Meier method and log-rank test were used for univariate analyses and the Cox proportional hazards model for multivariate analyses. In patients with lesions >20 mm, SRS and FSRT were compared (Fisher's exact/Chi square test) for age, gender, KPS, year of SRS/FSRT, primary tumor, number/site of lesions, systemic treatment, and extracranial metastases.

RESULTS

In patients with lesions >20 mm, significantly more patients receiving SRS had a KPS >80 than patients treated with FSRT (91% vs 29%, p = 0.002); otherwise, distributions of patient characteristics were balanced. In patients with lesions >20 mm, SRS was associated with significantly higher RN rates at 1 year (50% vs 9%) and 2 years (50% vs 9%) on univariate analysis (p = 0.012), which remained on multivariate analysis (HR: 0.10; 95% CI: 0.01-0.94, p = 0.044). No significant differences were found for LC (p = 0.21) at 1 year (75% vs 70%) and 2 years (75% vs 53%), and OS (p = 0.09) at 1 year (36% vs 59%) and 2 years (27% vs 46%). In patients with lesions ≤20 mm, 1- and 2-year RN rates following SRS were both 4%, compared to 0% and 15% respectively after FSRT (p = 0.60). In the SRS group, RN rates were significantly higher with lesions >20 mm (vs ≤20 mm) on univariate (p<0.001) and multivariate (HR: 3.82, 95% CI: 1.70-8.58, p = 0.001) analyses. In the FSRT group, max. diameter had no significant impact on RN rates (p = 0.93).

CONCLUSION

Given the limitations of this study, FSRT with BED >49 Gy12 appears associated with a low risk of RN when used for brain metastases >20 mm. SRS with 1x19-20 Gy may not be optimal for metastases >20 mm but appears safe for lesions ≤20 mm. Prospective trials are warranted.

Final Results of a Study Evaluating the Course of Distress Scores During Radiotherapy for Malignant Diseases

BACKGROUND/AIM

Patients who receive radiotherapy (RT) may experience significant distress. This study investigated distress scores during RT for a variety of malignancies.

PATIENTS AND METHODS

Distress thermometers (scores of 0-10 points) were completed by 927 patients at baseline and end of RT. Six characteristics were evaluated for changes of distress scores including age, sex, Karnofsky performance score (KPS), tumor type, intent of treatment, and previous RT.

RESULTS

Mean distress scores were 4.9 (±2.7) at baseline and 4.6 (±2.7) at the end of RT; mean change was -0.3 (±2.8) points. On univariable analysis, increased distress (≥2 points) was significantly associated with KPS 90-100 (p<0.001) and curative intent (p=0.040). Trends were found for age ≤64 years (p=0.062), head-and-neck cancer (p=0.076), and no prior RT (p=0.055). In patients with baseline scores ≤5 points, deterioration rates were 30-47%.

CONCLUSION

Psychological support should be offered to all patients undergoing RT. This would benefit particularly patients with risk factors for increased distress.

Distress Scores During Radiotherapy for Lung Cancer: Course and Prognostic Factors

Background/Aim

Cancer treatment can lead to significant distress. We investigated the course of distress during radiotherapy (RT) for lung cancer.

Patients and Methods

Data of 159 patients receiving RT for lung cancer were investigated for change of distress scores during RT. Five characteristics were analyzed including age, sex, Karnofsky performance score, intent of RT, and receipt of previous RT. Additional analyses were performed in patients with pre-RT scores ≤5 points.

Results

Mean pre-RT and post-RT distress scores were 5.5 (±2.6) and 4.7 (±2.6), respectively. No characteristic was significantly associated with mean change or increase of distress. In patients with pre-RT scores ≤5 points, non-significantly higher rates of increased distress were found for age ≤64 years, female sex, and Karnofsky performance score 90-100.

Conclusion

Distress is reduced during a course of RT for lung cancer. This may reflect a reduction in anticipatory distress after first-hand experience.

Comparison of Distress Scores Before and After Radiotherapy for Prostate Cancer

BACKGROUND/AIM

Prostate cancer patients undergoing radiotherapy (RT) may experience distress. This study evaluated the course of distress during RT.

PATIENTS AND METHODS

Four distress characteristics were analyzed for change of distress in 136 patients irradiated for prostate cancer, including age, Karnofsky performance score, intent of RT, and previous RT.

RESULTS

Mean distress scores were 4.3 (±2.9) at baseline and 4.2 (±2.7) at the end of RT. Associations with increased distress were found for KPS >80 (p<0.001) and curative intent RT (p=0.072). When evaluating increased distress as binary variable (yes vs. no), KPS >80 was significant on univariable (p<0.001) and multivariable (p=0.016) analyses. In patients with baseline scores ≤5 points, KPS >80 was associated with mean change of distress (p=0.009) and increased distress (p=0.029).

CONCLUSION

Many patients receiving RT for prostate cancer do not experience increased distress during their treatment course. Patients at higher risk of increased distress may require early psychological assistance.

Development of Distress During a Radiotherapy Course for Head-and-neck Cancer

BACKGROUND/AIM

Radiotherapy (RT) is a standard treatment for head-and-neck cancer, which can be associated with patient distress. This study provides data investigating distress during head-and-neck RT.

PATIENTS AND METHODS

Fifty-six patients completed the Distress Thermometer before and on the last day of their RT-course. Mean changes of distress scores and increase of distress were evaluated. Age, sex, Karnofsky performance score (KPS), tumor type, intent of RT, and previous RT were analyzed for associations with course of distress.

RESULTS

Mean pre-RT and post-RT distress scores were 5.1 (±2.6) and 5.0 (±2.7) points, respectively (mean change: ±0.0 points). Mean change of distress scores was significantly associated with age (p=0.042) and KPS (p<0.001). On multivariable analysis, increased distress (by ≥2 points) was associated with KPS 90-100 (p=0.011) and palliative intent of RT (p=0.036).

CONCLUSION

Mean pre-RT and post-RT distress scores were almost identical. Patients with risk factors for increased distress during their RT-course should be offered immediate psychological support.

A New Prognostic Instrument for Predicting the Probability of Completion of Cisplatin during Chemoradiation for Head and Neck Cancer

Many head and neck cancer patients assigned to definitive or adjuvant chemoradiation treatment do not complete the concurrent cisplatin dose. We determined corresponding risk factors and developed a prognostic instrument to help identify these patients. Ten pre-treatment characteristics were retrospectively analyzed in 154 patients with head and neck cancer who were treated via chemoradiation with cisplatin. These pre-treatment characteristics included age, sex, Karnofsky performance score, tumor site, primary tumor stage, nodal stage, histologic grade, upfront surgery, human papilloma virus status, and history of smoking. The characteristics significantly associated with the completion of cisplatin-based treatment, the receipt of ≥80% cisplatin, or showing a strong trend of association after multivariate analyses were used for the prognostic instrument. For each characteristic, 0 points were assigned for worse outcomes, and 1 point was assigned for better outcomes. Patients' scores were calculated by adding these points. Age ≤ 60 years and a Karnofsky performance score of 90-100 were significantly associated with both endpoints after multivariate analysis, and male gender showed a trend for association with the receipt of ≥80% cisplatin. Patient scores were 0, 1, 2, and 3 points. The corresponding rates of completion of cisplatin-based treatment were 14%, 41%, 62%, and 72%, respectively (p = 0.004). The rates of receipt of ≥80% cisplatin were 29%, 54%, 72%, and 94%, respectively (p < 0.001). This new prognostic instrument helps to predict whether head and neck cancer patients scheduled for chemoradiation will receive cisplatin as planned.

Hypo-fractionated Radiotherapy (HF-RT) Versus Conventionally Fractionated Radiotherapy (CF-RT) for Glioblastoma

BACKGROUND/AIM

Hypo-fractionated radiotherapy (HF-RT) is increasingly used for elderly and frail glioblastoma patients. In countries with limited radiotherapy capacities, HF-RT is more widely applied. This allowed us to compare conventional fractionation (CF-RT) vs. HF-RT in patients of any age and performance status.

PATIENTS AND METHODS

We retrospectively analysed 277 patients [110 HF-RT (52.5 Gy in 15 fractions) vs. 167 CF-RT (54.0-60.0 Gy in 27-33 fractions)] for local control (LC) and overall survival (OS) including subgroups considering specific patient characteristics.

RESULTS

On univariable comparisons, CF-RT was associated with significantly better LC and OS in patients with KPS ≤70 and unifocal glioblastoma, and with OS in the entire cohort. Trends were found for LC and OS in patients aged <60 years, and for OS in additional four subgroups. On multivariable analyses, improved LC and OS were significantly associated with CF-RT, KPS 80-100, unifocal glioblastoma, resection, and receipt of chemotherapy. Maximum diameter <45 mm was associated with improved OS.

CONCLUSION

Given the limitations of this study, CF-RT appeared associated with better outcomes. Selected patients may benefit from HF-RT.

Whole-brain Radiotherapy With or Without a Simultaneous Integrated Boost for Treatment of Brain Metastases

BACKGROUND/AIM

Many patients with brain metastases receive whole-brain radiotherapy (WBRT), despite the increasing use of stereotactic radiotherapy alone. A more recent approach includes WBRT combined with simultaneous integrated boost (WBRT+SIB). This study compared WBRT alone and WBRT+SIB for unresected brain metastases.

PATIENTS AND METHODS

One-hundred-and-three patients receiving WBRT+SIB were compared to 275 patients receiving WBRT alone for intracerebral control (IC) and overall survival (OS).

RESULTS

Both treatment groups (WBRT alone and WBRT+SIB) were balanced with respect to patient characteristics. On multivariate analyses, WBRT+SIB (p=0.041), Karnofsky performance score (KPS) >70 (p<0.001), and 1-3 brain metastases (p=0.016) were significantly associated with IC. KPS >70 (p<0.001), favorable tumor type (p=0.011), 1-3 brain metastases (p=0.011), and absence of extracranial metastases (p<0.001) were significantly associated with OS.

CONCLUSION

WBRT+SIB is associated with improved IC but similar OS when directly compared to WBRT for brain metastases. Selected patients with a high risk of intracerebral recurrence may benefit from SIB.

Chemoradiation with Cisplatin vs. Carboplatin for Squamous Cell Carcinoma of the Head and Neck (SCCHN)

Cisplatin is the standard for the chemoradiation of squamous cell carcinoma of the head and neck (HNSCC). Many patients cannot receive cisplatin due to impaired renal function. This study investigated carboplatin as an alternative option. In total, 131 patients assigned to two courses of cisplatin (20 mg/m²/d1--5 or 25 mg/m²/d1-4) were matched to 45 patients not suitable for cisplatin and receiving carboplatin (AUC 1.0/d1-5 or AUC 1.5/d1-4). The endpoints included loco-regional control (LRC), metastases-free survival (MFS), overall survival (OS), toxicities, and the completion of chemotherapy. The patients in the carboplatin group were significantly older and had more G3 tumors. Otherwise, the baseline characteristics were balanced. The LRC rates at 2 and 3 years were 77% and 76% in the cisplatin group vs. 69% and 65% in the carboplatin group (p = 0.21). The MFS rates were 83% and 78% vs. 78% and 74% (p = 0.34) and the OS rates 83% and 79% vs. 83% and 75% (p = 0.64), respectively. The outcomes were not significantly different in the subgroups receiving definitive or adjuvant chemoradiation. No significant differences were found regarding toxicities. Non-significantly more patients in the carboplatin group completed their chemotherapy (78% vs. 66%, p = 0.15). Carboplatin was associated with similar outcomes and toxicities as cisplatin, although these patients had worse renal function, more aggressive tumors, and were older. Given the limitations of this study, carboplatin appears an option for patients not suitable for cisplatin.

First Results of Concurrent Chemoradiation with Two Courses of 5 × 25 mg/m2 Cisplatin for Locally Advanced Head and Neck Cancer

Many patients with squamous cell carcinoma of the head and neck (SCCHN) receive cisplatin-based chemoradiation. Cisplatin 100 mg/m² every three weeks is toxic and alternative cisplatin regimens are desired. Two courses of 20 mg/m²/day 1-5 (cumulative 200 mg/m²) were shown to be similarly effective and better tolerated than 100 mg/m² every three weeks. Previous studies suggested that cumulative doses >200 mg/m² may further improve outcomes. In this study, 10 patients (group A) receiving two courses of 25 mg/m²/day 1-5 (cumulative 250 mg/m²) in 2022 were retrospectively matched and compared to 98 patients (group B) receiving two courses of 20 mg/m²/day 1-5 or 25 mg/m²/day 1-4 (cumulative 200 mg/m²). Follow-up was limited to 12 months to avoid bias. Group A achieved non-significantly better 12-month loco-regional control (100% vs. 83%, p = 0.27) and metastases-free survival (100% vs. 88%, p = 0.38), and similar overall survival (89% vs. 88%, p = 0.90). No significant differences were found regarding toxicities, completion of chemotherapy, and interruption of radiotherapy. Given the limitations of this study, chemoradiation with two courses of 25 mg/m²/day 1-5 appears an option for carefully selected patients as a personalized treatment approach. Longer follow-up and a larger sample size are needed to properly define its role.

Incremental retraining, clinical implementation, and acceptance rate of deep learning auto-segmentation for male pelvis in a multiuser environment

BACKGROUND

Deep learning auto-segmentation (DLAS) models have been adopted in the clinic; however, they suffer from performance deterioration owing to the clinical practice variability. Some commercial DLAS software provide an incremental retraining function that enables users to train a custom model using their institutional data to account for clinical practice variability.

PURPOSE

This study was performed to evaluate and implement the commercial DLAS software with the incremental retraining function for definitive treatment of patients with prostate cancer in a multi-user environment.

METHODS

CT-based target organs and organs-at-risk (OAR) delineation of 215 prostate cancer patients were utilized. The performance of three commercial DLAS software built-in models was validated with 20 patients. A retrained custom model was developed using 100 patients and evaluated on the remaining data (n = 115). Dice similarity coefficient (DSC), Hausdorff distance (HD), mean surface distance (MSD), and surface DSC (SDSC) were utilized for quantitative evaluation. A multi-rater qualitative evaluation was blindly performed with a five-level scale. Visual inspection was performed in consensus and non-consensus unacceptable cases to identify the failure modes.

RESULTS

Three commercial DLAS vendor built-in models achieved sub-optimal performance in 20 patients. The retrained custom model had a mean DSC of 0.82 for prostate, 0.48 for seminal vesicles (SV), and 0.92 for rectum, respectively. This represents a significant improvement over the built-in model with DSC of 0.73, 0.37, and 0.81 for the corresponding structures. Compared to the acceptance rate of 96.5% and consensus unacceptable rate (i.e., both reviewers rated as unacceptable) of 3.5% achieved by manual contours, the custom model achieved a 91.3% acceptance rate and 8.7% consensus unacceptable rate. The failure modes of retrained custom model were attributed to the following: cystogram (n = 2), hip prosthesis (n = 2), low dose rate brachytherapy seeds (n = 2), air in endorectal balloon(n = 1), non-iodinated spacer (n = 2), and giant bladder(n = 1).

CONCLUSION

The commercial DLAS software with the incremental retraining function was validated and clinically adopted for prostate patients in a multi-user environment. AI-based auto-delineation of the prostate and OARs is shown to achieve improved physician acceptance, overall clinical utility, and accuracy.

Stereotactic Radiotherapy or Whole-Brain Irradiation Plus Simultaneous Integrated Boost After Resection of Brain Metastases

BACKGROUND/AIM

Most patients with resected brain metastases receive post-operative radiotherapy. This study investigated outcomes of fractionated stereotactic radiotherapy (FSRT) alone or whole-brain irradiation plus simultaneous integrated boost (WBI+SIB) in the post-operative setting.

PATIENTS AND METHODS

Forty-four patients receiving FSRT alone (n=32) or WBI+SIB (n=12) after resection of 1-3 brain metastases from 2014-2022 were analyzed. Twelve factors were evaluated for local control (LC), distant brain control (DBC), and overall survival (OS).

RESULTS

On univariate and multivariate analyses, single brain metastasis was associated with improved LC and DBC. Longer interval between tumor diagnosis and radiotherapy, single brain metastasis, and Karnofsky performance score >80 were associated with improved OS. WBI+SIB showed a trend towards better DBC.

CONCLUSION

Several independent predictors of outcomes after FSRT or WBI+SIB following resection of brain metastases were identified. Given similar survival in the post-operative setting between FSRT and WBI+SIB, potential toxicity remains a significant factor in treatment recommendations.

Treatment Outcomes After Higher-dose Fractionated Stereotactic Radiotherapy (FSRT) Alone for 1-4 Brain Metastases

BACKGROUND/AIM

Fractionated stereotactic radiotherapy (FSRT) is increasingly used for brain metastases. We investigated higher-dose FSRT with biologically effective doses (BED) of 49.6-66.7 Gy₁₂ Patients and Methods: Eleven characteristics were evaluated for local control (LC), overall survival (OS), and freedom from radiation necrosis (RN) in 69 patients with 1-4 brain metastases. Fifty-seven patients (83%) had extracranial metastases, 23 (33%) Karnofsky performance scores (KPS) ≤70, and 21 (30%) brain metastases ≥21 mm.

RESULTS

At 1 and 2 years, LC-rates were 81% and 63%, OS-rates 66% and 43%, and freedom from RN-rates 98% and 87%, respectively. Median time to local progression was 35 months, median survival 19 months. KPS ≥90 was associated with better OS (p=0.048). BED of 49.6-57 Gy₁₂ (vs. 63-66.7 Gy₁₂) was associated with higher rates of freedom from RN (p=0.046), not with LC (p=0.78) or OS (p=0.55).

CONCLUSION

Higher-dose FSRT appears feasible and effective in patients with 1-4 brain metastases. BED 63-66.7 Gy₁₂ may not improve LC and OS but may increase RN risk.

Identification of Patients With Glioblastoma Who May Benefit from Hypofractionated Radiotherapy

BACKGROUND/AIM

Standard radiotherapy (RT) for glioblastoma lasts 6 weeks. We aimed to identify patients who would benefit from a hypofractionated approach.

PATIENTS AND METHODS

In 167 patients receiving standard fractionation, 10 factors were analyzed for local control (LC) and overall survival (OS). A survival score was developed and compared to a previous instrument.

RESULTS

On multivariate analysis, better LC was significantly associated with the presence of only one lesion and O⁶-methylguanine-DNA methyltransferase (MGMT) promoter methylation. Better OS was associated with one lesion, better performance status, MGMT promoter methylation, and receipt of chemotherapy. Lesion diameter ≤40 mm and upfront resection were associated with improved OS on univariate analyses. Based on assigning scores to these six factors, three groups, with 32-35, 36-44 and 45-48 points, were designed with 12-month OS-rates of 0%, 56%, and 92%, respectively. Accuracy in predicting death within 12 months and survival ≥12 months was 100% and 92%, respectively, versus 67% and 83% with the previous scoring system.

CONCLUSION

A new survival score with higher accuracy was developed for patients with glioblastoma. Our model can be utilized to individualize RT dose-fractionation recommendations for glioblastoma.

Beam mask and sliding window-facilitated deep learning-based accurate and efficient dose prediction for pencil beam scanning proton therapy

PURPOSE

To develop a DL-based PBSPT dose prediction workflow with high accuracy and balanced complexity to support on-line adaptive proton therapy clinical decision and subsequent replanning.

METHODS

PBSPT plans of 103 prostate cancer patients and 83 lung cancer patients previously treated at our institution were included in the study, each with CTs, structure sets, and plan doses calculated by the in-house developed Monte-Carlo dose engine. For the ablation study, we designed three experiments corresponding to the following three methods: 1) Experiment 1, the conventional region of interest (ROI) method. 2) Experiment 2, the beam mask (generated by raytracing of proton beams) method to improve proton dose prediction. 3) Experiment 3, the sliding window method for the model to focus on local details to further improve proton dose prediction. A fully connected 3D-Unet was adopted as the backbone. Dose volume histogram (DVH) indices, 3D Gamma passing rates, and dice coefficients for the structures enclosed by the iso-dose lines between the predicted and the ground truth doses were used as the evaluation metrics. The calculation time for each proton dose prediction was recorded to evaluate the method's efficiency.

RESULTS

Compared to the conventional ROI method, the beam mask method improved the agreement of DVH indices for both targets and OARs and the sliding window method further improved the agreement of the DVH indices. For the 3D Gamma passing rates in the target, OARs, and BODY (outside target and OARs), the beam mask method can improve the passing rates in these regions and the sliding window method further improved them. A similar trend was also observed for the dice coefficients. In fact, this trend was especially remarkable for relatively low prescription isodose lines. The dose predictions for all the testing cases were completed within 0.25s.

Emotional Distress in Head-and-neck Cancer Patients Scheduled for Chemoradiation or Radiotherapy Alone

BACKGROUND/AIM

Radiotherapy for head-and-neck cancer is often associated with significant toxicities, which may cause emotional distress. We evaluated prevalence and risk factors for pre-treatment emotional problems in patients irradiated for head-and-neck cancer.

PATIENTS AND METHODS

Twelve characteristics were retrospectively investigated in 213 patients for associations with emotional problems (worry, fear, sadness, depression, nervousness, loss of interest). After Bonferroni adjustment, p-values <0.0042 were regarded significant.

RESULTS

At least one emotional problem was reported by 131 patients (61.5%). Specific prevalence for emotional problems ranged between 10% and 44%. Physical complaints showed significant associations with all six emotional problems (p<0.0001) and female sex with sadness (p=0.0013). Trends were found for associations between female sex and fear (p=0.0097), history of another tumor and sadness (p=0.043), worse performance status and nervousness (p=0.012), and cancer site (oropharynx/oral cavity) and nervousness (p=0.063).

CONCLUSION

More than 60% of patients reported emotional distress prior to radiotherapy for head-and-neck cancer. Patients with risk factors likely require near-term psycho-oncological assistance.

Pre-treatment Emotional Distress in Patients Irradiated for Malignant Glioma

BACKGROUND/AIM

A recommendation of radiotherapy for patients with malignant gliomas may trigger emotional distress. Frequency and risk factors of this complication were investigated.

PATIENTS AND METHODS

Prevalence of six emotional problems and 11 potential risk factors were evaluated in 103 patients irradiated for grade II-IV gliomas. p-Values <0.0045 were considered significant.

RESULTS

Seventy-six patients (74%) had ≥1 emotional problem. Prevalence of specific emotional problems ranged between 23% and 63%. Associations were found between ≥5 physical problems and worry (p=0.0010), fear (p=0.0001), sadness (p=0.0023), depression (p=0.0006), and loss of interest (p=0.0006), and Karnofsky performance score ≤80 and depression (p=0.0002). Trends were found for physical problems and nervousness (p=0.040), age ≥60 years and depression (p=0.043) or loss of interest (p=0.045), grade IV glioma and sadness (p=0.042), and ≥2 involved sites and loss of interest (p=0.022).

CONCLUSION

Three-fourths of glioma patients had pre-radiotherapy emotional distress. Psychological support should be offered very soon, particularly for high-risk patients.

Emotional Distress Prior to Chemoradiation for Rectal or Anal Cancer

BACKGROUND/AIM

Anticipation of chemoradiation has been reported to cause psychosocial distress in patients with rectal cancer. This study provides additional data regarding prevalence and risk factors of emotional distress in patients who received chemoradiation for rectal or anal cancer.

PATIENTS AND METHODS

Sixty-four patients were analyzed for emotional distress utilizing 12 factors. When applying the Bonferroni correction, p-values <0.0042 were considered significant.

RESULTS

Worry, fears, sadness, depression, nervousness, and loss of interest in usual activities were reported by 31%, 47%, 33%, 11%, 47%, and 19% of patients, respectively. More physical problems were associated with fears (p=0.0030) and loss of interest (p=0.0021). Strong trends were observed for associations between female sex and sadness (p=0.0098) and between lower performance score and worry (p=0.0068) or fears (p=0.0064).

CONCLUSION

A considerable proportion of patients reported emotional distress prior to chemoradiation for rectal or anal cancer. High-risk patients may benefit from early psycho-oncological support.

Pre-treatment Emotional Distress in Patients Receiving Radiotherapy for Gynecologic Cancers

BACKGROUND/AIM

Patients with gynecologic cancers selected for external-beam radiotherapy or brachytherapy may experience emotional distress. We aimed to identify patients who may benefit from early psycho-oncological intervention.

PATIENTS AND METHODS

We investigated 10 potential risk factors of emotional distress in a retrospective series of 122 patients planned for radiotherapy of gynecologic cancers. Factors included COVID-19 pandemic, number of physical problems, age, performance status, tumor site/stage, surgery, chemotherapy, brachytherapy, and history of another tumor. p-Values <0.005 indicated significance, and p-values <0.06 trends.

RESULTS

Frequencies of worry, fear, sadness, depression, nervousness, and loss of interest were 41%, 57%, 39%, 16%, 38%, and 20%, respectively. Significant associations with at least one of these symptoms were found for ≥5 physical problems and no upfront surgery. Trends were observed for chemoradiotherapy, history of another tumor, worse performance status, and younger age.

CONCLUSION

The prevalence of pre-radiotherapy emotional distress was remarkable in patients with gynecologic cancers. Patients with risk factors may benefit from immediate psycho-oncological assistance.

Prevalence of and Risk Factors for Emotional Distress in Patients Undergoing Radiotherapy for Lung Cancer

BACKGROUND/AIM

Quality of life of patients with lung cancer can be impaired by psychological distress. This study evaluated prevalence of and risk factors for emotional distress in patients undergoing radiotherapy or chemoradiotherapy.

PATIENTS AND METHODS

Fourteen potential risk factors were retrospectively investigated in 144 patients. Emotional distress was evaluated with the National Comprehensive Cancer Network Distress Thermometer. Values of p<0.0036 (Bonferroni correction) were considered significant.

RESULTS

At least one emotional problem (worry, fear, sadness, depression, nervousness, loss of interest) was reported by the majority of patients (N=93, 65%). Prevalence of these problems was 37%, 38%, 31%, 15%, 32% and 23%, respectively. Physical problems were significantly associated with worry (p=0.0029), fear (p=0.0030), sadness (p<0.0001), depression (p=0.0008), nervousness (p<0.0001), and loss of interest (p<0.0001). Age ≤69 years was associated with worry (p=0.0003), and female sex with fear (p=0.0002) and sadness (p=0.0026). Trends were found for associations of age with sadness (p=0.045), female sex with nervousness (p=0.034), and chemoradiotherapy with worry (p=0.027).

CONCLUSION

Many patients with lung cancer experience emotional distress. Early psycho-oncological assistance may be important, particularly for high-risk patients.

Prevalence and Risk Factors of Emotional Distress in Patients With Prostate Cancer Assigned to External-beam Radiotherapy With or Without High-dose Rate Brachytherapy

BACKGROUND/AIM

Upcoming radiotherapy for prostate cancer may lead to emotional distress. This study aimed to identify the prevalence and risk factors in a retrospective cohort of 102 patients.

PATIENTS AND METHODS

Thirteen characteristics were evaluated for six emotional problems. To account for multiple comparisons, Bonferroni correction was used; p-values <0.0038 were significant (alpha level <0.05).

RESULTS

Prevalence of worry, fears, sadness, depression, nervousness, and loss of interest in usual activities was 25%, 27%, 11%, 11%, 18%, and 5%, respectively. A greater number of physical problems was significantly associated with worry (p=0.0037) and fears (p<0.0001) and showed trends regarding sadness (p=0.011) and depression (p=0.011). Trends were also found for associations between younger age and worry (p=0.021), advanced primary tumor stage and fears (p=0.025), patient's history of another malignancy and nervousness (p=0.035), and between external-beam radiotherapy alone and fears (p=0.042) or nervousness (p=0.037).

CONCLUSION

Although the prevalence of emotional distress was comparably low, patients with risk factors may benefit from early psychological support.

Radiation Necrosis Following Stereotactic Radiosurgery or Fractionated Stereotactic Radiotherapy with High Biologically Effective Doses for Large Brain Metastases

In Radiation Therapy Oncology Group 90-05, the maximum tolerated dose of single-fraction radiosurgery (SRS) for brain metastases of 21-30 mm was 18 Gy (biologically effective dose (BED) 45 Gy₁₂). Since the patients in this study received prior brain irradiation, tolerable BED may be >45 Gy₁₂ for de novo lesions. We investigated SRS and fractionated stereotactic radiotherapy (FSRT) with a higher BED for radiotherapy-naive lesions. Patients receiving SRS (19-20 Gy) and patients treated with FSRT (30-48 Gy in 3-12 fractions) with BED > 49 Gy₁₂ for up to 4 brain metastases were compared for grade ≥ 2 radiation necrosis (RN). In the entire cohort (169 patients with 218 lesions), 1-year and 2-year RN rates were 8% after SRS vs. 2% and 13% after FSRT (p = 0.73) in per-patient analyses, and 7% after SRS vs. 7% and 10% after FSRT (p = 0.59) in per-lesion analyses. For lesions ≤ 20 mm (137 patients with 185 lesions), the RN rates were 4% (SRS) vs. 0% and 15%, respectively, (FSRT) (p = 0.60) in per-patient analyses, and 3% (SRS) vs. 0% and 11%, respectively, (FSRT) (p = 0.80) in per-lesion analyses. For lesions > 20 mm (32 patients with 33 lesions), the RN rates were 50% (SRS) vs. 9% (FSRT) (p = 0.012) in both per-patient and per-lesion analyses. In the SRS group, a lesion size > 20 mm was significantly associated with RN; in the FSRT group, lesion size had no impact on RN. Given the limitations of this study, FSRT with BED > 49 Gy₁₂ was associated with low RN risk and may be safer than SRS for brain metastases > 20 mm.

Deep-Learning-based Fast and Accurate 3D CT Deformable Image Registration in Lung Cancer

PURPOSE

In some proton therapy facilities, patient alignment relies on two 2D orthogonal kV images, taken at fixed, oblique angles, as no 3D on-the-bed imaging is available. The visibility of the tumor in kV images is limited since the patient's 3D anatomy is projected onto a 2D plane, especially when the tumor is behind high-density structures such as bones. This can lead to large patient setup errors. A solution is to reconstruct the 3D CT image from the kV images obtained at the treatment isocenter in the treatment position.

METHODS

An asymmetric autoencoder-like network built with vision-transformer blocks was developed. The data was collected from 1 head and neck patient: 2 orthogonal kV images (1024x1024 voxels), 1 3D CT with padding (512x512x512) acquired from the in-room CT-on-rails before kVs were taken and 2 digitally-reconstructed-radiograph (DRR) images (512x512) based on the CT. We resampled kV images every 8 voxels and DRR and CT every 4 voxels, thus formed a dataset consisting of 262,144 samples, in which the images have a dimension of 128 for each direction. In training, both kV and DRR images were utilized, and the encoder was encouraged to learn the jointed feature map from both kV and DRR images. In testing, only independent kV images were used. The full-size synthetic CT (sCT) was achieved by concatenating the sCTs generated by the model according to their spatial information. The image quality of the synthetic CT (sCT) was evaluated using mean absolute error (MAE) and per-voxel-absolute-CT-number-difference volume histogram (CDVH).

RESULTS

The model achieved a speed of 2.1s and a MAE of <40HU. The CDVH showed that <5% of the voxels had a per-voxel-absolute-CT-number-difference larger than 185 HU.

CONCLUSION

A patient-specific vision-transformer-based network was developed and shown to be accurate and efficient to reconstruct 3D CT images from kV images.

The First Survival Score for Patients Treated with Whole-Brain Radiotherapy Plus Simultaneous Integrated Boost for Brain Metastases

A modern approach for brain metastases includes whole-brain radiotherapy plus simultaneous boost (WBRT+SIB). We developed a survival score in 128 patients treated with WBRT+SIB. Three models, each including three prognostic groups, were created. Positive predictive values (PPVs) for death ≤6 and survival ≥6 months were calculated. On multivariate analyses, performance score (KPS) and the number of brain metastases were significantly associated with survival. On univariate analyses, age showed a strong trend, and extra-cerebral cranial metastases a trend. In Model 1 (KPS, number of lesions), compared groups had 6-month survival rates of 15%, 38% and 57%. In Model 2 (KPS, lesions, age), rates were 17%, 33% and 75%, and in Model 3 (KPS, lesions, age, extra-cerebral metastases), 14%, 34% and 78%. PPVs for death ≤6 and survival ≥6 months were 85% and 57% (Model 1), 83% and 75% (Model 2), and 86% and 78% (Model 3). Thus, all models were accurate in predicting death ≤ 6 months; poor-prognosis patients may not benefit from SIB. Models 2 and 3 were superior in predicting survival ≥ 6 months. Given that Model 3 requires more data (including extensive staging), Model 2 is considered favorable for many patients. If extra-cerebral metastases are already known or extensive staging has been performed, Model 3 can also be used.

Evaluation of the Impact of Smoking and Alcohol Consumption on Toxicity and Outcomes of Chemoradiation for Head and Neck Cancer

BACKGROUND/AIM

Smoking and alcohol abuse may impair outcomes of chemoradiation for squamous cell head and neck cancer (SCCHN). Potential associations with toxicity, loco-regional control (LRC), and overall survival (OS) were investigated.

PATIENTS AND METHODS

Ninety-six patients were retrospectively analyzed for impacts of pre-radiotherapy (pre-RT) smoking history, smoking during radiotherapy, and pre-RT alcohol abuse on toxicity, LRC, and OS.

RESULTS

A trend was found for associations between pre-RT smoking history and grade ≥2 dermatitis. Smoking during radiotherapy was significantly associated with grade ≥3 mucositis and showed trends regarding grade ≥2 mucositis and dermatitis. On univariate analyses, smoking during radiotherapy was negatively associated with LRC and OS, pre-RT alcohol abuse with OS, and >40 pack years with LRC and OS. In multivariate analyses, smoking during radiotherapy remained significant for decreased OS, and pack years showed a trend.

CONCLUSION

Smoking during radiotherapy was an independent predictor of OS and associated with increased toxicity. Thus, it is important to stop smoking prior to the start of radiotherapy.

Clinical Practice Evolvement for Post-Operative Prostate Cancer Radiotherapy-Part 2: Feasibility of Margin Reduction for Fractionated Radiation Treatment with Advanced Image Guidance

Purpose: Planning target volume (PTV) expansion for post-prostatectomy radiotherapy is typically ≥5 mm. Recent clinical trials have proved the feasibility of a reduced margin of 2−3 mm for treatments on MRI-linac. We aim to study the minimum PTV margin needed using iterative cone-beam CT (iCBCT) as image guidance on conventional linacs. Materials/Methods: Fourteen patients who received post-prostatectomy irradiation (8 with an endorectal balloon and 6 without a balloon) were included in this study. Treatment was delivered with volumetric modulated radiation therapy (VMAT). Fractional dose delivery was evaluated in 165 treatment fractions. The bladder, rectal wall, femoral heads, and prostate bed clinical tumor volume (CTV) were contoured and verified on daily iCBCT. PTV margins (0 mm, 2 mm, and 4 mm) were evaluated on daily iCBCT. CTV coverage and OAR dose parameters were assessed with each PTV margin. Results: CTV D100% was underdosed with a 0 mm margin in 32% of fractions in comparison with 2 mm (6%) and 4 mm (6%) PTV margin (p ≤ 0.001). CTV D95% > 95% was met in 93−94% fractions for all PTV expansions. CTV D95% > 95% was achieved in more patients with an endorectal balloon than those without: 0 mm—90/91 (99%) vs. 63/74 (85%); 2 mm—90/91 (99%) vs. 65/75 (87%); 4 mm—90/90 (100%) vs. 63/73 (86%). There was no difference in absolute median change in CTV D95% (0.32%) for 0-, 2-, and 4 mm margins. The maximum dose remained under 108% for 100% (0 mm), 97% (2 mm), and 98% (4 mm) of images. Rectal wall maximum dose remained under 108% for 100% (0 mm), 100% (2 mm), and 98% (4 mm) of images. Conclusions: With high-quality iCBCT image guidance, PTV margin accounting for inter-fractional uncertainties can be safely reduced for post-prostatectomy radiotherapy. For fractionated radiotherapy, an isotropic expansion of 2 mm and 4 mm may be considered for margin expansion with and without the endorectal balloon. Future application for margin reduction needs to be further evaluated and considered with the advent of shorter post-prostatectomy radiation courses.

Clinical Practice Evolvement for Post-Operative Prostate Cancer Radiotherapy-Part 1: Consistent Organs at Risk Management with Advanced Image Guidance

Purpose: Post-operative prostate cancer patients are treated with full bladder instruction and the use of an endorectal balloon (ERB). We reassessed the efficacy of this practice based on daily image guidance and dose delivery using high-quality iterative reconstructed cone-beam CT (iCBCT). Methods: Fractional dose delivery was calculated on daily iCBCT for 314 fractions from 14 post-operative prostate patients (8 with and 6 without ERB) treated with volumetric modulated radiotherapy (VMAT). All patients were positioned using novel iCBCT during image guidance. The bladder, rectal wall, femoral heads, and prostate bed clinical tumor volume (CTV) were contoured and verified on daily iCBCT. The dose-volume parameters of the contoured organs at risk (OAR) and CTV coverage were assessed for the clinical impact of daily bladder volume variations and the use of ERB. Minimum bladder volume was studied, and a straightforward bladder instruction was explored for easy clinical adoption. Results: A “minimum bladder” contour, the overlap between the original bladder contour and a 15 mm anterior and superior expansion from prostate bed PTV, was confirmed to be effective in identifying cases that might fail a bladder constraint of V65% <60%. The average difference between the maximum and minimum bladder volumes for each patient was 277.1 mL. The daily bladder volumes varied from 62.4 to 590.7 mL and ranged from 29 to 286% of the corresponding planning bladder volume. The bladder constraint of V65% <60% was met in almost all fractions (98%). CTVs (D90%, D95%, and D98%) remained well-covered regardless of the absolute bladder volume daily variation or the presence of the endorectal balloon. Patients with an endorectal balloon showed smaller variation but a higher average maximum rectal wall dose (D0.03mL: 104.3% of the prescription) compared to patients without (103.3%). Conclusions: A “minimum bladder” contour was determined that can be easily generated and followed to ensure sufficient bladder sparing. Further analysis and validation are needed to confirm the utility of the minimal bladder contour. Accurate dose delivery can be achieved for prostate bed target coverage and OAR sparing with or without the use of ERB.

Technical note: Investigation of dose and LETd effect to rectum and bladder by using non-straight laterals in prostate cancer receiving proton therapy

BACKGROUND

Parallel-opposed lateral beams are the conventional beam arrangements in proton therapy for prostate cancer. However, when considering linear energy transfer (LET) and RBE effects, alternative beam arrangements should be investigated.

PURPOSE

To investigate the dose and dose averaged LET (LET_d ) impact of using new beam arrangements rotating beams 5°-15° posteriorly to the laterals in prostate cancer treated with pencil-beam-scanning (PBS) proton therapy.

METHODS

Twenty patients with localized prostate cancer were included in this study. Four proton treatment plans for each patient were generated utilizing 0°, 5°, 10°, and 15° posterior oblique beam pairs relative to parallel-opposed lateral beams. Dose-volume histograms (DVHs) from posterior oblique beams were analyzed. Dose-LET_d -volume histogram (DLVH) was employed to study the difference in dose and LET_d with each beam arrangement. DLVH indices, V ( d , l ) $V( {d,l} )$ , defined as the cumulative absolute volume that has a dose of at least d (Gy[RBE]) and a LET_d of at least l (keV/µm), were calculated for both the rectum and bladder to the whole group of patients and two-sub groups with and without hydrogel spacer. These metrics were tested using Wilcoxon signed-rank test.

RESULTS

Rotating beam angles from laterals to slightly posterior by 5°-15° reduced high LET_d volumes while it increased the dose volume in the rectum and increased LET_d in bladders. Beam angles rotated five degrees posteriorly from laterals (i.e., gantry in 95° and 265°) are proposed since they achieved the optimal balance of better LET_d sparing and minimal dose increase in the rectum. A reduction of V(50 Gy[RBE], 2.6 keV/µm) from 7.41 to 3.96 cc (p < 0.01), and a slight increase of V(50 Gy[RBE], 0 keV/µm) from 20.1 to 21.6 cc (p < 0.01) were observed for the group without hydrogel spacer. The LET_d sparing was less effective for the group with hydrogel spacer, which achieved the reduction of V(50 Gy[RBE], 2.6 keV/µm) from 4.28 to 2.10 cc (p < 0.01).

CONCLUSIONS

Posterior oblique angle plans improved LET_d sparing of the rectum while sacrificing LET_d sparing in the bladder in the treatment of prostate cancer with PBS. Beam angle modification from laterals to slightly posterior may be a strategy to redistribute LET_d and perhaps reduce rectal toxicity risks in prostate cancer patients treated with PBS. However, the effect is reduced for patients with hydrogel spacer.