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%, <i>p</i> &lt; .001), bowel V15 (949 vs. 191 cc, <i>p</i> = .001) and V30 (386 vs. 121 cc, <i>p</i> &lt; .001), rectum V40 (81.8 vs. 32.1%, <i>p</i> &lt; .001) and V50 (47.6 vs. 24.9%, <i>p</i> &lt; .001), femoral head maximum doses (46.4–47.1 vs. 38.3–38.6GyE, <i>p</i> &lt; .001), and bone V10 (93.3 vs. 85.4%, <i>p</i> &lt; . 001). Mean doses for all OARs were significantly higher with IMRT, including bladder (41.9 vs. 29.7GyE, <i>p</i> &lt; .001), bowel (21.2 vs. 5.5GyE, <i>p</i> &lt; .001), and rectum (50.8 vs. 27.3GyE, <i>p</i> &lt; .001). Integral dose to ‘Body – CTV’ was significantly higher with IMRT (32.8 vs. 18.4 J, <i>p</i> &lt; .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及盆腔淋巴结的治疗，调强光子放射治疗（Intensity-Modulated Photon Radiation Therapy, IMRT）与调强质子放射治疗（Intensity-Modulated Proton Therapy, IMPT）的头对头比较数据较为有限。本研究旨在评估术后全盆腔放射治疗（Whole Pelvis Radiation Therapy, WPRT）场景下，IMRT与IMPT的剂量学差异。本研究为2020年7月至8月期间接受治疗的10例前列腺切除术后患者制定了IMRT与IMPT计划。处方剂量为：盆腔区域50Gy生物等效剂量（GyE，质子生物有效剂量换算系数为1.1），前列腺床区域70GyE，分割方式为每次2GyE。采用配对双侧Wilcoxon符号秩检验比较临床靶区（Clinical Target Volume, CTV）的覆盖情况及危及器官（Organs at Risk, OARs）的受照剂量。所有计划均满足CTV覆盖要求，99%的CTV接受了≥99%的处方剂量。IMRT组的危及器官受照剂量显著高于IMPT组，涉及的评估终点包括：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。存在显著差异的具体评估终点包括：膀胱V30（63.5% vs 44.4%，*p* < 0.001）、肠道V15（949 vs 191 cc，*p* = 0.001）与V30（386 vs 121 cc，*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 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在IMRT组中均显著更高，其中膀胱为（41.9 vs 29.7 GyE，*p* < 0.001）、肠道为（21.2 vs 5.5 GyE，*p* < 0.001）、直肠为（50.8 vs 27.3 GyE，*p* < 0.001）。“全身-CTV”的积分剂量在IMRT组中显著更高（32.8 vs 18.4 J，*p* < 0.001）。本研究结果显示，在前列腺癌术后全盆腔放射治疗中，IMPT的靶区覆盖度与IMRT相当，但可显著降低危及器官的受照剂量。上述数据可为未来前列腺癌术后放射治疗的临床管理与实施提供参考依据。