Background. An incidental axillary dose of adjuvant radiotherapy using tangential beams is usually given after breast-conserving surgery for breast cancer. The goal of this sub-study was to evaluate this incidental dose in the setting of post-mastectomy radiotherapy (PMRT) according to two different radiotherapy techniques. Methods. Patients participating in a randomized SERC trial who received PMRT in a single center were included. We collected the incidental axillary dose delivered to the Berg level 1 using different dosimetric parameters and compared two techniques using Student’st-test: three-dimensional conformal radiotherapy (3D-CRT) and volumetric arc therapy (VMAT). Results. We analyzed radiotherapy plans from 52 patients who received PMRT from 2012 to 2021. The mean dose delivered to the Berg level 1 was 37.2 Gy. It was significantly higher with VMAT than with 3D-CRT—43.6 Gy (SD = 3.1 Gy) versus 34.8 Gy (SD = 8.6 Gy)p< 0.001. Eighty-four percent of the Berg level 1 was covered by 40 Gy isodose in the VMAT group versus 55.5% in the 3D-CRT groupp< 0.001. Conclusions. On the Berg level 1, PMRT gives a dose at least equivalent to the one given by post-breast-conserving surgery radiotherapy, making it possible to limit completion axillary lymph node dissections in select pN1a patients treated with a mastectomy. Modern radiotherapy techniques like VMAT tend to increase this incidental dose.
背景：乳腺癌保乳术后通常采用切线野放疗技术给予腋窝区域辅助性附带照射剂量。本亚组研究旨在评估两种不同放疗技术下，乳房切除术后放疗（PMRT）中该附带剂量的分布情况。方法：纳入参与SERC随机试验并在单一中心接受PMRT的患者。通过不同剂量学参数收集Berg 1级淋巴结区域的附带照射剂量，并采用Student t检验比较三维适形放疗（3D-CRT）与容积旋转调强放疗（VMAT）两种技术。结果：分析2012年至2021年间52例接受PMRT患者的放疗计划。Berg 1级淋巴结区域平均受照剂量为37.2 Gy。VMAT组剂量显著高于3D-CRT组（43.6 Gy ± 3.1 Gy vs 34.8 Gy ± 8.6 Gy，p<0.001）。VMAT组中84%的Berg 1级区域被40 Gy等剂量线覆盖，而3D-CRT组仅为55.5%（p<0.001）。结论：PMRT在Berg 1级淋巴结区域产生的剂量至少等同于保乳术后放疗剂量，这使得部分接受乳房切除术的pN1a患者可能避免补充腋窝淋巴结清扫。VMAT等现代放疗技术倾向于增加该附带剂量。
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