肺癌CT及X线模拟定位放疗计划的剂量学比较研究

Dosimetric comparison between CT and X-ray simulation of radiotherapy for lung cancer

目的探讨肺癌不同定位方法在肿瘤覆盖和正常组织保护上的优劣。方法对33例肺癌病例同时进行X线和CT模拟定位,采用3DTPS设计X线模拟定位的4个野照射常规计划（RT）、CT模拟定位的4个野照射二维计划（2D）和三维适形放疗计划（3DCRT）,总剂量均为50 Gy。用剂量体积直方图（DVH）比较3种计划的肿瘤覆盖、剂量分布和正常组织受照剂量差异。结果3DCRT和2D计划在靶区覆盖、靶区剂量、适形性和均匀性方面均优于RT计划（P＜0．05）。3DCRT的靶区适形指数（TCI）和均匀性（TH）均较2D计划高（P＜0．05）,3DCRT和2D在靶区覆盖、靶区剂量差异无统计学意义（P＞0．05）。与RT和2D相比,3DCRT等剂量线的高剂量区所包括的肺和心脏体积均小（P＜0．05）。3DCRT与2D相比减少了V20、V30和MLD（P＜0．05）,而与RT相比差别无统计学意义（P＞0．05）。脊髓剂量3DCRT与RT和2D计划间相比差别有统计学意义（P＜0．05）,食管和心脏剂量在3DCRT、2D和RT计划间差别均无统计学意义（P＞0．05）。结论CT较X线模拟定位能更加明确地确定靶区,通过3DTPS设计可获得靶区理想的剂量分布。3DCRT在靶区适形度和均匀性上优于2D计划。3DCRT能够减少肺受照体积和剂量。在脊髓、食管、心脏剂量上均能控制在正常组织耐受剂量范围以内。

Objective To compare radiotherapy plan of conventional X-ray simulation with CT simulation by 3D-TPS for lung cancer. Methods Thirty-three patients were allotted to receive both conventional X-ray simulation and CT simulation in the same treatment position. 3D-TPS was used to design 4-field conventional plan of X-ray simulation （RT）, 4-field two dimensional plan （2D）and three dimensional conformal radiation plan（3DCRT）of CT simulation for all patients. The total dose was 50 Gy. Dose volume histogram（DVH） was applied to evaluate the difference of target coverage, dose distribution and normal tissue protection among the three plans. Results 3DCRT and 2D based on CT simulation were superior to RT in the target coverage, target conformity index（ TCI ） and target homogeneity （ TH ） （ P 〈 0.05 ）. The TCI and TH of 3DCRT were significantly higher than those of 2D（ P 〈0.05 ）. Compared to RT and 2D,3DCRT decreased the volume of the normal lung and heart tissue covered by the 90% isodose. V20, V3o and mean lung dose were similar among 3DCRT, 2D and RT plans. Moreover, the maximum doses of spinal cord were significantly different among the three plans. No statistical differences of doses to 30% of the heart and esophagus volume among the three plans were observed. Conclusions There is significantly better tumour volume coverage in CT simulation when compared with X-ray conventional simulation. Target volume delineation by CT simulation is improved significantly. The dose distribution is improved by using three dimensional treatment planning system. 3DCRT plan is superior to 2D plans in target conformity index and target homogeneity. Doses delivered to organs surrounding the target such as lung and heart were reduced significantly in 3 DCRT.