基于剂量重建分析摆位误差对海马保护性全脑预防照射的剂量学影响

The Analysis of Dosimetric Effects of Setup Errors on Hippocampus Avoidance Prophylactic Cranial Irradiation Based on Dose Reconstruction

目的 手动模拟三维6个方向的摆位误差,探讨其对海马保护性全脑预防照射中靶区和危及器官受照剂量的影响。方法 选取医院2021年12月至2022年8月收治的10例自愿接受海马保护的脑转移患者,通过移动计划等中心坐标,模拟患者在三维6个方向上的摆位误差,将1、3、5 mm的摆位误差引入原计划进行剂量重建,得到新的剂量分布。结果 当摆位误差在5 mm以内时,各方向上计划靶区(PTV)D95%的剂量差异变化均小于2%,头方向剂量变化最大;均匀性指数(HI)最大变化不超过2%;适形度指数(CI)100%最大变化不超过5%。当摆位误差为1 mm时,海马最大剂量偏差发生在背方向(Y正方向),为5.42%;当摆位误差为3 mm和5 mm时,海马最大剂量偏差均发生在头方向(Z正方向),分别为17.02%和28.16%。当摆位误差分别为1、3、5 mm时,晶体最大剂量偏差均发生在脚方向(Z负方向),分别为7.75%,39.43%和73.34%。结论 摆位误差对周围正常组织剂量的影响远远大于靶区,且剂量变化数值随摆位误差增大而增大。因此在海马保护性全脑预防放射治疗中建议增加锥形束CT(CBCT)辅助摆位,以减小摆位误差带来的剂量偏差,尤其需要注意头脚方向。

Objective With the setup errors in six directions in three dimensions by the manual simulation, its effect on the radiation dose of the target area and endangered organs in the hippocampus avoidance prophylactic cranial irradiation was investigated.Methods With selection of 10 patients with brain metastases who voluntarily received hippocampus protection from December 2021 to August 2022 in the hospital,the setup errors of the patients in six directions in three dimensions were simulated, by moving the isocenter coordinates of the plan. 1, 3, and 5 mm setup errors were introduced into the original plan for dose reconstruction to obtain a new dose distribution. Results With the setup errors within 5 mm, the dose differences of the planned target area(PTV) D95% in each direction were less than 2%, and the dose change in the head direction was the largest;The maximum variation of homogeneity index(HI) did not exceed 2%, and the maximum variation of conformal index(CI)100% did not exceed 5%.With 1 mm setup error, the maximum dose deviation of the hippocampus occurred in the posterior direction(Y positive direction), which was 5.42%. With the setup error of 3 mm and 5 mm, the maximum dose deviation of the hippocampus occurred in the superior direction(Z positive direction), which was 17.02% and 28.16%, respectively. With the setup error of 1 mm, 3 mm and 5 mm, the maximum dose deviation of lens occurred in the inferior direction(Z negative direction), which was 7.75%, 39.43% and 73.34%, respectively. Conclusions The influence of setup error on the dose of surrounding normal tissues is far greater than that of the target area, and the dose change value increases with the increase of setup error. Therefore, it is recommended to add cone-beam CT(CBCT) auxiliary positioning in radiotherapy to reduce the dose deviation caused by setup error, especially the superior and inferior directions.