有无均整器模式下早期左侧乳腺癌患者放疗后辐射致癌风险比较

Radiotherapy-induced secondary primary cancer risks for early breast cancer： flattening filter versus flattening filter free IMRT radiotherapy

目的 对早期、左侧乳腺癌患者采用6 MV X射线有均整器（FF）与无均整器（FFF）模式固定野动态调强放疗（d-IMRT）技术放疗后的辐射致癌风险进行比较，为临床放疗技术的选择提供参考。方法 采用6 MV X射线有、无均整器模式两种放疗技术分别对20例早期、左侧乳腺癌患者设计两野共面动态调强治疗计划。在95%体积的计划靶区（PTV）、临床靶区（CTV）满足处方剂量的前提下，通过调整射野参数和计划优化参数，尽量降低周围危及器官的剂量。非均整模式下调强计划的射野参数和计划优化参数与均整模式下相应参数一致。进而，通过辐射致癌风险模型计算，比较两组治疗计划右侧乳腺、肺、甲状腺、肝脏等危及器官的辐射致癌风险。结果 两组计划的靶区均达到临床处方剂量的要求。FFF模式计划中右侧乳腺、肺、甲状腺、肝脏等器官的当量剂量（OED）和超额绝对风险（EAR）均相对小于均整模式计划中的相应值，差异有统计学意义（t=2.18~9.72，2.11~9.99，P〈0.05）。采用FFF模式能明显降低右侧乳腺当量剂量和超额绝对风险。结论 早期、左侧乳腺癌患者放疗中采用6 MV X射线有、无均整器模式调强放疗技术，其靶区和危及器官受照剂量均能满足临床治疗要求。FFF模式能降低右侧乳腺、肺、甲状腺、肝脏等器官的超额绝对风险。

Objective To evaluate the secondary cancer risk to various organs due to radiation treatment for early left-sided breast cancer using 6 MV X-ray flattening filter free （FFF） and flattening filter （FF） modes. Methods Two techniques, 6 MV FFF and 6 MV FF X-rays modes, were used to develop the two tangential fields d-IMRT plans for 20 early left-sided breast cancer patients respectively. For all the patients, the dose to surrounding tissues was minimized as low as possible, the 95% volume of the planning target volume （PTV） and clinical target volume （CTV） was consistent with the prescribed dose. The beam parameters and the plan optimization parameters of FFF modes were in consonance with FF modes. The radiation doses and volumes of the planning target volumes, organs at risk and normal tissue were detected by dose-volume histogram. And then, the excess absolute risk（EAR） of contralateral breast, ipsilateral lung, contralateral lung, thyroid and liver were calculated using the radiotherapy-induced secondary primary cancer risks models. Results The treatment plans of two groups met the requirements of clinical. The FFF d-IMRT techniques resulted in a systematic reduction of the organ equivalent dose （OED） （t=2.18-9.72, P〈0.05）, and the EAR （t=2.11-9.99, P〈0.05） of contralateral breast, ipsilateral lung, contralateral lung, thyroid and liver was compared to the FF IMRT techniques, especially for the contralateral breast. Conclusions Both FFF and FF d-IMRT plans can achieve comparable target dose coverage in patients with early left-sided breast cancer, while the FFF d-IMRT techniques could reduce the excess absolute risk of contralateral breast, ipsilateral lung, contralateral lung, thyroid and liver. These results are of clinical importance, especially for the early-stage patients with an overall good prognosis.