Radiation Oncology Department, American University of Beirut Medical Center, Beirut, Lebanon.
Lebanese Atomic Energy Commission, Beirut, Lebanon.
Phys Med Biol. 2022 Jul 25;67(15). doi: 10.1088/1361-6560/ac7c50.
This study aims at quantifying the lifetime attributable risk of secondary fatal cancer (LARFAC) to patients receiving adjuvant radiotherapy treatment for thymoma, a neoplasm where cure rates and life expectancy are relatively high, patient age at presentation relatively low and indications for radiotherapy controversial depending on the disease stage.An anthropomorphic phantom was scanned, organs were contoured and a standard 6 MV 3DCRT treatment plan was produced for thymoma treatment. The phantom was loaded with thermoluminescent dosimeters (TLDs) and treated by linear accelerator per plan. The TLDs were subsequently read for out-of-field dose distribution while in-field dose distribution was obtained from the planning system. Sex and age-specific lifetime radiogenic cancer risk was calculated as the sum of in-field risk and out-of-field risk. The latter risk was estimated using hybrid ICRP 2007 103-BEIR VII tables of organ-specific risks based on the linear-no threshold (LNT) model and applicable at low doses, while the former using mathematical risk models applicable at high doses.The LARFAC associated with a prescribed dose of 50 Gy to target volume in 25 fractions was in the approximate range of 1%-3%. The risk was higher for young and female patients. The largest contributing organ to this risk were the lungs by far. Using the LNT model inappropriately to calculate risk at therapeutic doses (in-field) would overestimate the risk up to tenfold.The LARFAC to patient from thymoma radiotherapy was quantified taking into consideration the inapplicability of the LNT model at therapeutic doses. The risk is not negligible; the information may be relevant to patients and clinicians.
本研究旨在量化接受胸腺瘤辅助放疗的患者发生继发性致命癌症（LARFAC）的终生归因风险。胸腺瘤是一种治愈率和预期寿命相对较高、患者发病年龄相对较低的肿瘤，其放疗指征因疾病分期而异，目前尚存争议。
对一个人体模型进行了扫描，对器官进行了轮廓勾画，并为胸腺瘤治疗制定了标准的 6 MV 3DCRT 治疗计划。在模型中放入了热释光剂量计（TLDs），并按计划用直线加速器进行了治疗。随后，通过 TLD 测量了场外剂量分布，而场内剂量分布则通过计划系统获得。基于线性无阈（LNT）模型和适用于低剂量的可应用于低剂量的 ICRP 2007 103-BEIR VII 器官特异性风险表，计算了特定性别和年龄的终生放射性致癌风险，该风险是场内风险和场外风险的总和。而前者则使用适用于高剂量的数学风险模型。
对于 50 Gy 的靶区处方剂量和 25 个分次的治疗方案，LARFAC 约为 1%-3%。对于年轻和女性患者，风险更高。到目前为止，对该风险贡献最大的器官是肺部。在治疗剂量（场内）下不恰当地使用 LNT 模型来计算风险会使风险高估十倍。
本研究考虑到 LNT 模型在治疗剂量下的不适用性，量化了胸腺瘤放疗患者的 LARFAC。风险不可忽视，这些信息可能与患者和临床医生有关。
