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[目的]观察调强放疗(IMRT)计划中规定处方剂量(致死剂量DT70Gy及预防剂量DT56Gy)的等剂量曲线外围邻近组织的剂量变化,评价不同医师对靶区勾画的差异所造成的的剂量学影响。[方法]20例初诊鼻咽癌患者,按照IMRT的治疗流程予以靶区勾画及计划设计。将IMRT计划中70Gy及56Gy的等剂量曲线所包含的体积范围定义为V70及V56。围绕V70及V56分别均匀外扩0.5cm及1cm所包含的体积范围,并“挖除”原有V70及V56部分分别形成的“戒指状”体积部分,定义为V70+0.5,V70+1及V56+0.5,V56+1。分别绘制V70+0.5,V70+1及V56+0.5,V56+1的剂量体积直方图(DVH),同时分别计算D50、D95。[结果]V70+0.5、V70+1、V56+0.5和V56+1的D50分别为65.94Gy、62.28Gy、51.51Gy和47.03Gy;D95分别为58.86Gy、49.66Gy、38.87Gy和29.03Gy。[结论]IMRT治疗计划中,处方剂量外0.5～1cm处区域存在较高的放射剂量,靶区勾画差异所引起的“剂量缺失”并不显著。
[Objective] To observe the changes of dose in adjacent tissues in the isodose curve prescribed by the IMRT program, and to evaluate the difference in dosimetry caused by different physicians’ delineation of the target area influences. [Methods] Twenty patients with newly diagnosed nasopharyngeal carcinoma were screened and planned according to the treatment schedule of IMRT. The volume ranges covered by the isograd curves of 70 Gy and 56 Gy in the IMRT plan were defined as V70 and V56. Around V70 and V56 were evenly expanded 0.5cm and 1cm contained in the volume range and “Dig ” original V70 and V56 part of the formation of the “ring” part of the volume, defined as V70 +0.5, V70 +1 and V56 + 0.5, V56 + 1. The dose volume histograms (DVH) of V70 + 0.5, V70 + 1 and V56 + 0.5, V56 + 1 were plotted, and D50 and D95 were calculated respectively. [Result] The D50 values of V70 + 0.5, V70 + 1, V56 + 0.5 and V56 + 1 were 65.94Gy, 62.28Gy, 51.51Gy and 47.03Gy, respectively. The D95 values were 58.86Gy, 49.66Gy, 38.87Gy and 29.03Gy, respectively. [Conclusion] In the IMRT treatment plan, there is a high radiation dose in the region of 0.5 ~ 1cm outside the prescription dose, and the “dose loss” caused by the difference in the target area is not significant.