基于剂量重建分析摆位误差对鼻腔NK/T细胞淋巴瘤剂量学影响

Dosimetric effect of set-up errors on nasal NK/T cell lymphoma based on dose reconstruction

目的通过将摆位误差引入放疗计划系统进行剂量重建,分析放疗摆位误差对鼻腔NK/T细胞淋巴瘤剂量学影响。方法选取10例鼻腔NK/T细胞淋巴瘤患者,对每一患者CT图像及靶区设计非共面容积旋转调强计划,计划完成后通过改变治疗等中心点参数,将摆位误差引入放疗计划中再进行剂量计算重建剂量分布。结果随系统摆位误差增加,靶区剂量逐渐下降,影响大小顺序为左右方向>头脚方向>前后方向。各方向平移摆位误差在-3~3 mm以及旋转摆位误差在-3°~3°内,靶区剂量变化范围均<±3%。各方向摆位误差≤3 mm时危及器官均在处方剂量附近,>3 mm时眼晶体、脊髓、腮腺、视神经逐渐超出处方剂量范围;旋转摆位误差仅当≥3°时眼晶体超量,尤其注意左右方向较大的摆位误差对眼晶体、脊髓、腮腺的影响和前后方向较大的摆位误差对脊髓的影响。引入本单位实际摆位误差后对GTV、CTV受量影响很小,均<±2%;少数危及器官有超出处方剂量限值风险,尤其要注意晶体和视神经超量。结论摆位误差将会导致鼻腔NK/T细胞淋巴瘤靶区剂量欠量以及危及器官超量,左右方向摆位误差影响尤为大,3 mm和3°内单一方向摆位误差对靶区和危及器官影响有限,建议将单一方向摆位误差控制在3 mm和3°内。引入本单位实际摆位误差对靶区受量影响很小,但少数危及器官有超出处方剂量限值风险,需增加对危及器官外扩区域评价。

Objective To evaluate the dosimetric effects of set-up errors on nasal NK/T cell lymphoma by introducing set-up errors into the radiotherapy planning system for dose reconstruction.Methods Ten patients with nasal NK/T cell lymphoma were recruited.A non-coplanar volumetric modulated arc therapy plan was designed for CT image and clinical target area of each patient.After the completion of the plan,the set-up errors were introduced into the radiotherapy plan by changing the ISO of the treatment,and dose calculation was performed to reconstruct the dose distribution.Results With the increase of system set-up errors,the dose of target was decreased and the order affected by set-up errors in different directions was:left-right direction>head-foot direction>front-rear direction.When the translational set-up errors in each direction were-3 mm to 3 mm and the rotating set-up errors were-3°to 3°,the range of dose change in all targets was less than±3%.When the set-up errors in all directions were≤3 mm,the dose of organ at risk was less than or similar to the prescribed dose.When the set-up errors were>3 mm,the doses of lens,spinal cord,parotid gland and optic nerve gradually exceeded the prescribed dose.Only when the rotating set-up errors were≥3°,the dose of lens exceeded the prescribed dose.Special attention should be paid to the influence of the greater set-up errors in the left and right direction on lens,spinal cord and parotid gland,as well as on the spinal cord due to the larger set-up errors in the front and rear direction.After the actual set-up errors were introduced from our department,it exerted slight effect on the irradiation dose of GTV and CTV,which was less than±2%.In a few cases,the dose of organ at risk potentially exceeded the prescribed dose limit,and special attention should be diverted to overdose of the lens and optic nerve.Conclusions The set-up errors will result in target dose deficiency and overdose of organ at risk in nasal NK/T cell lymphoma,especially upon the set-up errors in the left and right direction.The effect of 3 mm and 3°set-up errors on target and organ at risk is limited.Therefore,it is recommended to maintain the single direction set-up errors within 3 mm and 3°.The actual set-up errors introduced from our department exert little effect on the target dose,but a small number of organs are at risk of exceeding the prescribed dose limit.It is necessary to increase the evaluation of the extension region of organ at risk.