特殊体模及膀胱充盈状态对直肠癌术后辅助放疗的影响

Influence of belly board device and the distended bladder on dosimetric analysis and normal tissue complication in postoperative radiation therapy of rectal cancer

目的比较特殊体模及膀胱充盈状态对直肠癌术后放疗剂量分布及正常组织受照射体积的影响，探讨直肠癌术后适形放疗较理想的治疗模式。方法共有23例直肠癌患者入选。8例和15例患者分别采用膀胱充盈条件下常规或特殊体模固定的俯卧位3野照射，处方剂量50Gy。15例患者CT定位同时还扫描膀胱排空状态下的图像。运用三维计划系统比较3种照射方式的靶区和正常组织体积-剂量关系、适形指数（CIPTV）、特殊体模及膀胱充盈状态对不同剂量水平（5～52．5Gy）小肠受照射体积影响以及小肠急性放射性反应与受照射体积的关系。结果3种照射模式中靶区和股骨头体积．剂量分布及适形指数均无明显差异（P〉0．05）。但采用特殊体模照射时，小肠在高剂量区内体积（V20～V52.5）均显著减少（P〈0．01），且在膀胱充盈时更加明显，而低剂量区受照射体积（V5～V15）则减少不明显（P〉0．05）；膀胱充盈状态下使用特殊体模还可显著降低不同剂量水平（20-52．5Gy）膀胱受照射体积（P〈0．01）。照射过程中患者腹泻程度（RTOG0～1和≥2）与低剂量区内（5～30Gy）小肠受照射体积均显著相关（P〈0．05）。结论膀胱充盈状态下特殊体模固定的俯卧位照射方式明显降低了小肠和膀胱的受照射剂量，减少了小肠急性放射反应的发生。

Objective To evaluate the influence of belly board device and the distended bladder on the dose distribution of PTV and the dose-volume histograms（DVHs） of organs at risk （OARs） for postoperative radiation therapy of rectal cancer. Methods A total of 23 patients （8 and 15） with distended bladder receiving 3-field postoperative radiation therapy were dealed with or without a special belly board in the prone position. At the same time, 15 cases with belly board were scanned with empty bladder. The volume of irradiated small bowel was calculated for doses between 5-50 Gy at 5 Gy intervals. With prescription dose in plan target volume （PTV） of 50 Gy, we compared the dose distribution, DVH of OARs, conformity index （ CIpvv ）, the volume of irradiated small bowel and the acute toxicity under the condition of three different moulds. Results There was no significant difference in PTV＇ s converge, DVHs of femoral head and CI among 3 moulds（ P 〉 0.05）. With the belly board, the high-dose volume of irradiated small bowel （V20-V52.5 ） was significantly decreased（ P 〈 0.05）, specially with distended bladder. However, the low dose volume（ V5-V15 ） was slightly increased. The bladder distension significantly decreases the volumes of the irradiated small bowel at dose levels from 15-52.5 Gy（ P 〈 0.05）. Furthermore, the mean volume （Vs-V30）of irradiated small bowel differed significantly between patients experiencing Grade 0-1 and ≥ 2 diarrhea （P 〈 0.05 ）. Conclusions The combination of belly board and distended bladder was more effectively to reduce the irradiated small bowel volume among 3 moulds, so as to minimized acute diarrhea toxicity.