Background:Moderate hypofractionated radiotherapy (MHRT) has emerged as the preferred treatment modality for localized prostate cancer based on randomized controlled studies regarding efficacy and toxicity using contemporary radiotherapy techniques. In the setting of MHRT, available data on dosimetric parameters and late rectal toxicity are limited.Aim:To present the effects of MHRT on late rectal toxicity while conducting an extensive dosimetric analysis in conjunction with rectoscopy results.Methods:This is a prospective study including patients with intermediate-risk prostate adenocarcinoma. All patients were treated with MHRT 44 Gy in 16 fractions to the seminal vesicles and to the prostate, followed by a sequential boost to the prostate alone of 16.5 Gy in 6 fractions delivered with three-dimensional conformal radiation therapy (3DCRT). Acute and late toxicity were assessed. Endoscopy was performed at baseline, every 3 months post-therapy for the first year, and every 6 months for the year after. The Vienna Rectoscopy Score (VRS) was used to assess rectal mucosal injury related to radiotherapy. Dosimetric analysis for the rectum, rectal wall, and its subsegments (upper, mid, and low 1/3) was performed.Results:Between September 2015 and December 2019, 20 patients enrolled. Grade 1 late gastrointestinal toxicity occurred in 10% of the patients, whereas 5% had a grade ≥2. Twelve months post radiotherapy: 4 (20%) patients had VRS 1; 2 (10%) patients had VRS 2; 1(5%) patient had VRS 3. 24 months post radiotherapy, VRS 1 was observed in 4 patients (20%) and VRS 2 in 3 (15%) patients. The dosimetric analysis demonstrated noticeable variations between the rectum, rectal wall, and rectal wall subsegments. The dosimetric analysis of the rectum, rectal wall, and its mid and low segments with respect to rectoscopy findings showed that the higher dose endpoints V52.17Gyand V56.52Gyare associated with rectal mucosal injury.Conclusions:A thorough delineation of the rectal wall and its subsegments, together with the dosimetric analysis of these structures, may reduce late rectal toxicity. Dosimetric parameters such as V52.17Gyand V56.52Gywere identified to have a significant impact on rectal mucosal injury; additional dose endpoint validation and its relation to late GI toxicity is needed.
背景：基于采用现代放疗技术的疗效与毒性随机对照研究，中等程度大分割放疗（MHRT）已成为局限性前列腺癌的首选治疗方式。在MHRT背景下，关于剂量学参数与晚期直肠毒性的现有数据有限。 目的：在结合直肠镜检查结果进行广泛剂量学分析的同时，探讨MHRT对晚期直肠毒性的影响。 方法：本研究为前瞻性研究，纳入中危前列腺腺癌患者。所有患者均接受MHRT治疗，精囊和前列腺照射44 Gy/16次，随后仅对前列腺进行序贯加量照射16.5 Gy/6次，采用三维适形放疗（3DCRT）技术。评估急性和晚期毒性。在基线、治疗后第一年每3个月、第二年每6个月进行内镜检查。采用维也纳直肠镜评分（VRS）评估与放疗相关的直肠黏膜损伤。对直肠、直肠壁及其亚段（上、中、下1/3）进行剂量学分析。 结果：2015年9月至2019年12月期间，共纳入20例患者。10%的患者出现1级晚期胃肠道毒性，5%的患者出现≥2级毒性。放疗后12个月：4例（20%）患者VRS为1；2例（10%）患者VRS为2；1例（5%）患者VRS为3。放疗后24个月，4例（20%）患者观察到VRS 1，3例（15%）患者观察到VRS 2。剂量学分析显示直肠、直肠壁及直肠壁亚段之间存在显著差异。结合直肠镜检查结果对直肠、直肠壁及其中、下段进行的剂量学分析表明，较高剂量端点V52.17Gy和V56.52Gy与直肠黏膜损伤相关。 结论：对直肠壁及其亚段的精确勾画，结合对这些结构的剂量学分析，可能降低晚期直肠毒性。已确定V52.17Gy和V56.52Gy等剂量学参数对直肠黏膜损伤有显著影响；需要进一步验证这些剂量端点及其与晚期胃肠道毒性的关系。
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