Mazonakis Michalis, Kachris Stefanos, Damilakis John
Department of Medical Physics, Faculty of Medicine, University of Crete, P.O. Box 2208, Iraklion, Crete, 71003, Greece.
Department of Radiotherapy and Oncology, University Hospital of Iraklion, Iraklion, Crete, 71110, Greece.
Med Phys. 2020 Jul;47(7):2805-2813. doi: 10.1002/mp.14169. Epub 2020 Apr 30.
To estimate the risk for bladder and rectal cancer induction due to standard fractionated (SF) and moderately hypofractionated (HF) volumetric modulated arc therapy (VMAT) for prostate carcinoma.
Twelve patients with low or intermediate-risk of prostate cancer referred for external-beam radiotherapy were included in this study. Three computed tomography-based VMAT plans were created for each study participant. The first plan was generated by assuming patient's irradiation with SF-VMAT (78 Gy in 39 fractions). The second and third plans were created on the basis of two different HF schedules (HF-VMAT : 70 Gy in 30 fractions, HF:VMAT : 60 Gy in 20 fractions). Data from differential dose-volume histograms obtained by the above treatment plans were employed to calculate the organ equivalent dose (OED) of the bladder and rectum with the aid of a nonlinear model accounting for fractionation and proliferation effects. The calculated OED values were used to estimate the average lifetime attributable risk (LAR ) for the appearance of radiotherapy-induced secondary bladder and rectal malignancies. The lifetime risk of radiation carcinogenesis was compared with the respective organ-, and age-dependent lifetime intrinsic risk (LIR) of cancer development for unexposed males.
The average OED of the rectum from SF-VMAT, HF-VMAT and HF-VMAT for prostate cancer was 972.0, 900.2, and 815.7 cGy, respectively. The corresponding values for bladder were 73.4, 72.3, and 71.0 cGy. The LAR for rectal cancer induction varied from 0.06% to 0.4% by the fractionation schedule used for irradiation and by the age of the patient at the time of treatment. The corresponding risk range related to the development of secondary bladder malignancies was 0.06-0.33%. The SF-VMAT, HF-VMAT and HF-VMAT led to an increase of the lifetime rectal cancer risk with respect to LIR by 2.2-9.8%, 2.0-9.1% and 1.8-8.2%, respectively, depending upon the patient's age. The corresponding elevation for bladder cancer induction was up to 8.0%, 7.9% and 7.7%.
The use of VMAT for prostate carcinoma leads to a noteworthy increase of the lifetime risk for bladder and rectal cancer induction compared to that of unexposed people irrespective of the patient's age at the time of treatment and the applied fractionation scheme. The cancer risk data presented in this study may be taken into account by radiation oncologists and medical physicists in the selection of the optimal radiation therapy plan.
评估标准分割（SF）和适度低分割（HF）容积调强弧形放疗（VMAT）用于前列腺癌治疗时诱发膀胱癌和直肠癌的风险。
本研究纳入了12例因前列腺癌接受外照射放疗的低危或中危患者。为每位研究参与者制定了3个基于计算机断层扫描的VMAT计划。第一个计划是假设患者接受SF-VMAT照射（39次分割，总剂量78 Gy）生成的。第二个和第三个计划是根据两种不同的HF方案制定的（HF-VMAT：30次分割，总剂量70 Gy；HF-VMAT：20次分割，总剂量60 Gy）。利用上述治疗计划获得的差异剂量体积直方图数据，借助考虑分割和增殖效应的非线性模型计算膀胱和直肠的器官等效剂量（OED）。计算得到的OED值用于估计放疗诱发继发性膀胱癌和直肠癌的平均终生归因风险（LAR）。将辐射致癌的终生风险与未暴露男性相应器官及年龄相关的癌症发生终生固有风险（LIR）进行比较。
前列腺癌患者接受SF-VMAT、HF-VMAT和HF-VMAT治疗后，直肠的平均OED分别为972.0、900.2和815.7 cGy。膀胱的相应值分别为73.4、72.3和71.0 cGy。根据照射所用的分割方案和治疗时患者的年龄，诱发直肠癌的LAR在0.06%至0.4%之间变化。与继发性膀胱癌发生相关的相应风险范围为0.06 - 0.33%。SF-VMAT、HF-VMAT和HF-VMAT导致直肠癌终生风险相对于LIR分别增加2.2 - 9.8%、2.0 - 9.1%和1.8 - 8.2%，具体取决于患者年龄。膀胱癌诱发的相应升高分别高达8.0%、7.9%和7.7%。
无论治疗时患者的年龄以及所采用的分割方案如何, 与未暴露人群相比，VMAT用于前列腺癌治疗会导致膀胱癌和直肠癌诱发的终生风险显著增加。本研究中呈现的癌症风险数据可供放射肿瘤学家和医学物理学家在选择最佳放疗计划时参考。
