兆伏级锥形束CT成像剂量及其致继发肿瘤终生归因风险研究

Evaluation of the radiation dose and the lifetime attributable secondary malignancies risk associated with mega-voltage cone beam computed tomographic scanning

目的 评估胸部影像引导放射治疗中,兆伏级锥形束CT(MV-CBCT)成像在不同年龄患者各重要器官沉积的剂量,并预测成像剂量致继发肿瘤的终生归因风险(LAR)。方法 回顾性评估2018-02-01-2021-10-31山东省肿瘤防治研究院收治的206例年龄为3~70岁患者胸部MV-CBCT计划系统模拟的心脏、双侧肺、双侧乳腺等器官平均剂量和脊髓最大点剂量。建立成像野内器官剂量与胸围尺寸的线性关系。使用美国电离辐射生物效应委员会(BEIR)Ⅶ模型,预测MV-CBCT致不同年龄患者继发肿瘤的风险值。结果 206例患者以10 cm(头脚方向)×28 cm(左右方向)的开野范围模拟MV-CBCT扫描,其心脏、双侧肺、双侧乳腺和脊髓单次扫描的中位剂量分别为4.3(3.6~5.3)、2.7(1.9~5.0)、4.5(3.6~5.8)和3.7(2.8~4.9) cGy。射野内各器官平均剂量随着胸围的增大而单调减小。不同肿瘤LAR均随暴露年龄增大而降低。暴露年龄段为3~<10、10~<20、30~<40、50~<60和60~<70岁的男性肺癌LAR分别为2 539/10万人、1 729/10万人、750/10万人、649/10万人和594/10万人;女性分别为6 108/10万人、3 948/10万人、1 744/10万人、1 497/10万人和1 296/10万人。结论 在影像引导放射治疗过程中,MV-CBCT致成像野内器官的累积剂量可达约100 cGy,如叠加治疗场内低剂量区域,MV-CBCT增加继发肿瘤LAR则不可忽视。特别是暴露辐射年龄较小的儿童患者,制定放疗计划时应将该成像剂量潜在风险考虑在内。

Objective To evaluate mega-voltage cone beam computed tomography(MV-CBCT)doses to various critical or-gans and estimate the lifetime attributable secondary malignancies risk under imageguided thoracic radiotherapy.Methods Mean doses to the heart,lungs,breast and maximum point dose to the spinal cord due to thoracic MV-CBCT scans were retrospectively simulated on treatment planning system in 206 patients aged 3-70 years who were treated in Shandong Cancer Hospital and Institute during February 1,2018 to October 31,2021.We established a linear relationship between organ doses and chest size in the imaging field.The American Council on Biological Effects of Ionizing Radiation(BEIR)VI cancer risk prediction model was used to calculate the lifetime attributable risk of MV-CBCT induced secondary malignancies.Results For all 206 patients,the median doses of single scan simulated by 10 cm(superior-inferior)X 28 cm(lateral)MV-CBCT imaging field for the heart,spinal cord,lungs,and breast were 4.3(3.6-5.3)cGy,2.7(1.9-5.0)cGy,4.5(3.6-5.8)cGy and 3.7(2.8-4.9)cGy,respectively.The mean doses of organs at risk decreased monotonically with the chest circumference increases.The lifetime attributable risk for all tumors decreases with the age increases at MV-CBCT irradiation exposure.The lifetime attributable risk at secondary lung cancer for men/women exposed age groups of 3-<10,10-<20,30-<40,50-<60 and 60-<70 yearsold was 2539/6108,1729/3948,750/1744,649/1497 and 594/1296 per 100000 populations,respectively.Conclusions During image-guided radiation therapy,the cumulative daily MV-CBCT dose to organs in the field may be high at about 10o cGy,which may induce a non-negligible risk of secondary malignancies if doses in low-dose areas were overlain in the treatment field.The potential risk of MV-CBCT imaging dose should be taken into account during radiotherapy treatment planning,especially for pediatric patients with radiation exposed at young age.