直肠癌术前同期加量放疗三种不同照射技术的剂量学比较

目的 探讨直肠癌术前同期加量三维适形放疗（three-dimensional conformal radiotherapy，3DCRT）、静态调强放疗（intensity-modulated radiotherapy，IMRT） 和螺旋断层放疗（helical tomotherapy，HT） 的剂量学特点，为临床选择直肠癌术前放疗方法提供依据。 方法 对10 例Ⅱ～Ⅲ期直肠癌术前同步放化疗患者分别进行3 野3DCRT、9 野IMRT 和HT 的计划设计，统一给予肿瘤原发病灶及转移淋巴结（pGTV） 处方剂量56.25 Gy（ 分25 次），高危复发区域和区域淋巴引流区（PTV）50 Gy（ 分25 次）。利用剂量体积直方图评价靶区剂量分布以及危及器官的照射剂量。 结果 3 种治疗计划均能满足靶区处方剂量要求；除3DCRT 计划外，IMRT 计划和HT 计划均能满足各危及器官剂量限制要求。靶区（ 包括pGTV 和PTV） 适形指数HT ＜ IMRT ＜ 3DCRT，pGTV 剂量均匀指数HT ＜ IMRT 及3DCRT。对危及器官的保护IMRT 和HT 优于3DCRT，HT 优于IMRT。3DCRT、IMRT 和HT 计划的小肠V 15 分别为（304.7±113.2） cc、（283.5±124.8） cc 和（240.7±102.0） cc，两两差异均有统计学意义。 结论 此处方剂量模式下，3DCRT 计划无法满足危及器官剂量限制要求。直肠癌术前同期加量放疗中IMRT 和HT 计划在靶区适形度和危及器官保护方面均明显优于3DCRT 计划。HT 较IMRT 计划进一步降低了小肠、膀胱、骨盆及股骨头的照射剂量。

Radiometry of 3 different radiotherapies for rectal cancer before operation

Objective To provide the evidence for the selection of radiotherapy for rectal cancer before operation by comparing the radiometry characteristics of helical tomotherapy （HT）, step-and-shoot intensity-modulated radiotherapy （IMRT） and 3-dimensional conformal radiotherapy （3DCRT）. Methods Ten patients with stage Ⅱ - Ⅲ rectal cancer underwent HT, 9-field IMRT and 3-field 3DCRT at the dose of 56.25 Gy for the pGTV and at the dose of 50 Gy for the PTV in 25 fractions. The dose distribution in target areas and involved organs was assessed according to the dose-volume histogram. Results All 3 radiotherapies could meet the prescribed dose for the target areas. IMRT and HT but not 3DCRT could meet the prescribed dose for the involved organs. The conformity index （CI） of 3DCRT for the target areas （pGTV and PTV） was higher than that of IMRT and HT （P 〈 0.05） and the homogeneity index （HI） of HT for the pGTV was lower than that of IMRT and 3DCRT （P 〈 0.05）, indicating that IMRT and HT protected the involved organs better than 3DCRT, and HT protected the involved organs better than IMRT. The intestine V 15 was 304.7 ± 113.2 cc, 283.5 ± 124.8 cc and 240.7 ± 102.0 cc, respectively, for 3DCRT, IMRT and HT. Conclusion 3DCRT cannot meet the prescribed dose for the involved organs. IMRT and HT are significantly advantageous over 3DCRT in conformity of target areas and protection of involved organs. The effect of HT is better than that of IMRT and 3DCRT in reducing the irradiation dose for intestine, bladder, pelvic and femoral head.