Department of Radiation Oncology, University Medical Centre Mannheim, University of Heidelberg, Germany.
Radiat Oncol. 2011 Dec 16;6:174. doi: 10.1186/1748-717X-6-174.
Radiation induced secondary cancers are a rare but severe late effect after breast conserving therapy. Intraoperative radiotherapy (IORT) is increasingly used during breast conserving surgery. The purpose of this analysis was to estimate secondary cancer risks after IORT compared to other modalities of breast radiotherapy (APBI - accelerated partial breast irradiation, EBRT - external beam radiotherapy).
Computer-tomography scans of an anthropomorphic phantom were acquired with an INTRABEAM IORT applicator (diameter 4 cm) in the outer quadrant of the breast and transferred via DICOM to the treatment planning system. Ipsilateral breast, contralateral breast, ipsilateral lung, contralateral lung, spine and heart were contoured. An INTRABEAM source (50 kV) was defined with the tip of the drift tube at the center of the spherical applicator. A dose of 20 Gy at 0 mm depth from the applicator surface was prescribed for IORT and 34 Gy (5 days × 2 × 3.4 Gy) at 10 mm depth for APBI. For EBRT a total dose of 50 Gy in 2 Gy fractions was planned using two tangential fields with wedges. The mean and maximal doses, DVHs and volumes receiving more than 0.1 Gy and 4 Gy of organs at risk (OAR) were calculated and compared. The life time risk for secondary cancers was estimated according to NCRP report 116.
IORT delivered the lowest maximal doses to contralateral breast (< 0.3 Gy), ipsilateral (1.8 Gy) and contralateral lung (< 0.3 Gy), heart (1 Gy) and spine (< 0.3 Gy). In comparison, maximal doses for APBI were 2-5 times higher. EBRT delivered a maximal dose of 10.4 Gy to the contralateral breast and 53 Gy to the ipsilateral lung. OAR volumes receiving more than 4 Gy were 0% for IORT, < 2% for APBI and up to 10% for EBRT (ipsilateral lung). The estimated risk for secondary cancer in the respective OAR is considerably lower after IORT and/or APBI as compared to EBRT.
The calculations for maximal doses and volumes of OAR suggest that the risk of secondary cancer induction after IORT is lower than compared to APBI and EBRT.
放射诱导的继发性癌症是保乳治疗后罕见但严重的晚期效应。术中放疗（IORT）在保乳手术中越来越多地使用。本分析的目的是估计与其他乳房放疗方式（APBI-加速部分乳房照射，EBRT-外部束放疗）相比，IORT 后的继发性癌症风险。
使用 INTRABEAM IORT 施源器（直径 4 厘米）在外象限的乳房上获取人体模型的计算机断层扫描，并通过 DICOM 传输到治疗计划系统。对同侧乳房、对侧乳房、同侧肺、对侧肺、脊柱和心脏进行轮廓勾画。将漂移管的尖端定义为球形施源器中心的 INTRABEAM 源（50 kV）。规定 IORT 表面下 0 毫米处的 20 Gy 剂量和 APBI 表面下 10 毫米处的 34 Gy（5 天×2×3.4 Gy）。对于 EBRT，使用楔形物的两个切线野计划 50 Gy 的总剂量，2 Gy 分数。计算并比较了器官受照量（OAR）超过 0.1 Gy 和 4 Gy 的平均和最大剂量、DVH 和体积，并进行了比较。根据 NCRP 报告 116 计算了继发性癌症的终生风险。
IORT 对同侧（1.8 Gy）和对侧（<0.3 Gy）肺、心脏（1 Gy）和脊柱（<0.3 Gy）的最大剂量均最低。相比之下，APBI 的最大剂量高 2-5 倍。EBRT 对侧乳房最大剂量为 10.4 Gy，同侧肺最大剂量为 53 Gy。OAR 体积超过 4 Gy 的比例为 IORT 为 0%，APBI 为<2%，EBRT 为高达 10%（同侧肺）。与 EBRT 相比，IORT 和/或 APBI 后 OAR 的继发性癌症风险估计要低得多。
OAR 的最大剂量和体积计算表明，IORT 后诱导继发性癌症的风险低于 APBI 和 EBRT。
