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

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. 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). 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). 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.目前针对前列腺癌术后前列腺床与盆腔淋巴结照射场景，比较调强光子放射治疗（intensity-modulated photon radiotherapy, IMRT）与调强质子放射治疗（intensity-modulated proton radiotherapy, IMPT）疗效的相关数据较为有限。本研究旨在评估前列腺癌术后全盆腔放疗（whole pelvis radiation therapy, WPRT）场景下，IMRT与IMPT的剂量学差异。研究纳入2020年7月至8月期间接受前列腺切除术的10例患者，分别制定IMRT与IMPT治疗计划。处方剂量设置为：盆腔区域生物等效剂量（GyE）50 Gy（质子放射生物有效剂量系数为1.1），前列腺床区域生物等效剂量70 Gy，分割方式为每次分割剂量2 GyE。采用配对双侧Wilcoxon符号秩检验，比较两组计划的临床靶区（clinical target volume, CTV）覆盖度与危及器官（organs at risk, OARs）受照剂量。所有计划均满足CTV覆盖要求，99%的CTV可接收≥99%的处方剂量。IMRT计划的危及器官受照剂量显著高于IMPT计划，具体涵盖以下研究终点：膀胱V5~V65、肠道V5~V45、乙状结肠V5~V50、直肠V5~V70、股骨头V40及最大受照剂量、骨骼V5~V65。具有统计学差异的典型研究终点包括：膀胱V30（63.5% vs 44.4%，p<0.001）、肠道V15（949 cm³ vs 191 cm³，p=0.001）与V30（386 cm³ vs 121 cm³，p<0.001）、直肠V40（81.8% vs 32.1%，p<0.001）与V50（47.6% vs 24.9%，p<0.001）、股骨头最大受照剂量（46.4~47.1 GyE vs 38.3~38.6 GyE，p<0.001）以及骨骼V10（93.3% vs 85.4%，p<0.001）。所有危及器官的平均受照剂量，IMRT计划均显著高于IMPT计划：膀胱平均剂量（41.9 GyE vs 29.7 GyE，p<0.001）、肠道平均剂量（21.2 GyE vs 5.5 GyE，p<0.001）、直肠平均剂量（50.8 GyE vs 27.3 GyE，p<0.001）。除临床靶区外的全身积分剂量，IMRT计划显著更高（32.8 J vs 18.4 J，p<0.001）。前列腺癌术后全盆腔放疗场景下，IMPT计划的靶区覆盖度与IMRT计划相当，但可显著降低危及器官的受照剂量。本研究数据可为前列腺癌术后前列腺床放疗的临床决策与实施提供参考依据。