In silico comparison of whole pelvis intensity-modulated photon versus proton therapy for the postoperative management of prostate cancer.

BACKGROUND: Limited data exist comparing intensity-modulated photon (IMRT) and proton (IMPT) radiation therapy when treating the prostate bed and pelvic lymph nodes in the postoperative setting for prostate cancer. The aim of this study was to evaluate dosimetric differences between IMRT and IMPT when treating with whole pelvis radiation therapy (WPRT) postoperatively. MATERIALS AND METHODS: IMRT and IMPT plans were generated for 10 post-prostatectomy patients treated between July and August 2020. The prescription was 50 Gy radiobiologic equivalent (GyE) (proton radiobiological effective dose 1.1) to the pelvis and 70 GyE to the prostate bed in 2 GyE per fraction. Paired 2-sided Wilcoxon signed-rank tests were used to compare clinical target volume (CTV) coverage and dose to organs at risk (OARs). RESULTS: CTV coverage was met for all plans with 99% of CTVs receiving ≥99% of prescription doses. Dose to OARs was significantly higher with IMRT than IMPT for the following endpoints: bladder V5-V65; bowel V5-V45; sigmoid V5-V50; rectum V5-V70; femoral head V40 and maximum dose; bone V5-V65. Select endpoints with significant differences included bladder V30 (63.5 vs. 44.4%, p < .001), bowel V15 (949 vs. 191 cc, p = .001) and V30 (386 vs. 121 cc, p < .001), rectum V40 (81.8 vs. 32.1%, p < .001) and V50 (47.6 vs. 24.9%, p < .001), femoral head maximum doses (46.4-47.1 vs. 38.3-38.6GyE, p < .001), and bone V10 (93.3 vs. 85.4%, p < . 001). Mean doses for all OARs were significantly higher with IMRT, including bladder (41.9 vs. 29.7GyE, p < .001), bowel (21.2 vs. 5.5GyE, p < .001), and rectum (50.8 vs. 27.3GyE, p < .001). Integral dose to 'Body - CTV' was significantly higher with IMRT (32.8 vs. 18.4 J, p < .001). CONCLUSION: IMPT provides comparable target coverage to IMRT when treating prostate cancer with WPRT in the postoperative setting while significantly reducing dose to OARs. These data can inform the future clinical management and delivery of post-prostatectomy irradiation for prostate cancer.

In Silico Comparison of Three Different Beam Arrangements for Intensity-Modulated Proton Therapy for Postoperative Whole Pelvic Irradiation of Prostate Cancer.

Background and purpose: Proton therapy has been shown to provide dosimetric benefits in comparison with IMRT when treating prostate cancer with whole pelvis radiation; however, the optimal proton beam arrangement has yet to be established. The aim of this study was to evaluate three different intensity-modulated proton therapy (IMPT) beam arrangements when treating the prostate bed and pelvis in the postoperative setting. Materials and Methods: Twenty-three post-prostatectomy patients were planned using three different beam arrangements: two-field (IMPT2B) (opposed laterals), three-field (IMPT3B) (opposed laterals inferiorly matched to a posterior-anterior beam superiorly), and four-field (IMPT4B) (opposed laterals inferiorly matched to two posterior oblique beams superiorly) arrangements. The prescription was 50 Gy radiobiological equivalent (GyE) to the pelvis and 70 GyE to the prostate bed. Comparisons were made using paired two-sided Wilcoxon signed-rank tests. Results: CTV coverages were met for all IMPT plans, with 99% of CTVs receiving ≥ 100% of prescription doses. All organ at risk (OAR) objectives were met with IMPT3B and IMPT4B plans, while several rectum objectives were exceeded by IMPT2B plans. IMPT4B provided the lowest doses to OARs for the majority of analyzed outcomes, with significantly lower doses than IMPT2B +/- IMPT3B for bladder V30-V50 and mean dose; bowel V15-V45 and mean dose; sigmoid maximum dose; rectum V40-V72.1, maximum dose, and mean dose; femoral head V37-40 and maximum dose; bone V40 and mean dose; penile bulb mean dose; and skin maximum dose. Conclusion: This study is the first to compare proton beam arrangements when treating the prostate bed and pelvis. four-field plans provided better sparing of the bladder, bowel, and rectum than 2- and three-field plans. The data presented herein may help inform the future delivery of whole pelvis IMPT for prostate cancer.

I Can't Breathe: The Continued Disproportionate Exclusion of Black Physicians in the United States Radiation Oncology Workforce.

PURPOSE: Black physicians remain disproportionately underrepresented in certain medical specialties, yet comprehensive assessments in radiation oncology (RO) are lacking. Our purpose was to report current and historical representation trends for Black physicians in the US RO workforce. METHODS AND MATERIALS: Public registries were used to assess significant differences in 2016 representation for US vs RO Black academic full-time faculty, residents, and applicants. Historical changes from 1970 to 2016 were reported descriptively. Linear regression was used to assess significant changes for Black residents and faculty from 1995 to 2016. RESULTS: In 2016, Black people represented 3.2% vs 1.5% (P < .001), 5.6% vs 3.2% (P = .005), and 6.5% vs 5.4% (P = .352) of US vs RO faculty, residents, and applicants, respectively. Although RO residents nearly doubled from 374 (1974) to 720 (2016), Black residents peaked at 31 in 1984 (5.9%; 31 of 522) and fell to 23 (3.2%; 23 of 720) in 2016 across 91 accredited programs; Black US graduate medical education trainees nearly doubled over the same period: 3506 (1984) to 6905 (2016). From 1995 to 2016, Black US resident representation significantly increased by 0.03%/y, but decreased significantly in RO by -0.20%/y before 2006 and did not change significantly thereafter. Over the same period, Black US faculty representation significantly increased by 0.02%/y, whereas Black RO faculty significantly increased by 0.07%/y before 2006, then decreased significantly by -0.16%/y thereafter. The number of Black RO faculty peaked at 37 in 2006 (3.1%; 37 of 1203) and was 27 (1.5%; 27 of 1769) in 2016, despite the nearly 1.5-fold increase in the number of both RO faculty and Black US faculty overall (4169 in 2006 and 6047 in 2016) during that period. CONCLUSIONS: Black physicians remain disproportionately underrepresented in RO despite an increasing available pipeline in the US physician workforce. Deliberate efforts to understand barriers to specialty training and inclusion, along with evidence-based targeted interventions to overcome them, are needed to ensure diversification of the RO physician workforce.