自由呼吸状态下三维CT和四维CT极限时相全乳正向调强放疗治疗计划的比较

Evaluation of dosimetric variance in forward intensity modulated radiotherapy of the breast based on4D CT and 3D CT during free breathing

目的探讨保乳术后基于四维CT（4DCT）呼吸极限时相和常规三维CT（3DCT）定位图像问全乳正向调强放疗（IMRT）治疗计划间剂量学参数的差异。方法17例乳腺癌保乳术后患者于自由呼吸状态下序贯完成3DCT和4DCT扫描，以4DCT的rm时相为基准时相，在110时相CT图像上制定全乳正向IMRT计划，将110时相的IMRT计划复制到T50和3DCT图像上，比较3个计划间靶区和危及器官相关剂量体积参数的差异。结果17例患者11D时相与3DCT图像上勾画的CTV体积差异最大，体积差异中位数为4．10cm^3。TO时相PTV平均剂量高于T50时相（P=0．019），3DCT与TO、T50比较，差异均无统计学意义（均P〉0．05）。TO、T50、3DCT计划均匀性指数分别为0．149、0．159、0．164，仅，TO时相与T50时相差异有统计学意义（P=0．039）；TO与T50、3DCT计划适形指数间差异均有统计学意义（均P〈0．05），T50与3DCT差异无统计学意义（P=0．758）。T50时相肺脏V40、V50。均低于TD时相，差异均有统计学意义（均P〈0．05）。3个计划间心脏各参数差异比较，均无统计学意义（均P〉0．05）。结论自由呼吸状态下，全乳放疗中乳腺固有体积变化可以忽略，基于3DCT定位实施全乳正向IMRT是可行的，基于4DCT定位并辅助呼吸门控更准确。

Objective To explore the dosimetric variance in forward intensity modulated radiotherapy （IMRT） based on 4D CT and 3D CT after breast conserving surgery. Methods Seventeen patients after breast conserving surgery underwent 3D CT simulation scans followed by respiration- synchronized 4D CT simulation scans at free breathing state. The treatment plan constructed using the end inspiration （EI） scan was then copied and applied to the end expiration （EE）, and 3D scans and dose distribution were calculated separately. Dose-volume histograms （DVHs） parameters for the CTV, PTV, ipsilateral lung and heart were evaluated and compared. Results The CTV volume difference was biggest between TO and 3D CT, and the volume difference was g. 10 cm3. Mean dose of PTV at EE was lower than that at EI （P =0. 019） ,but there were no statistically significant difference between 3D and EI, EE （ all P 〉 O. 05 ）. The homogeneity index （HI） at EI, EE, 3D plans were 0. 149, 0. 159 and O. 164, respectively, and a significant difference was only between EI and EE （P =0.039）. The highest conformal index （CI） was at EI phase （P 〈0.05）, and there was no significant difference between EE and 3D （P =0.758）. The V40 and Vs0 of ipsilateral lung at EE phase were lower than that at EI （ P 〈 O. 05）. There were no significant differences in all the indexes for heart （P 〉 0.05）. Conclusions The breast deformation during respiration may be disregarded in whole breast IMRT. PTV dose distribution is significantly changed between EI and EE phases, and the differentiation of the lung high dose area between EI and EE phases may be induced by thorax expansion. 3D treatment planning is sufficient for whole breast forward IMRT, but dD CT scans assisted by respiratory gating ensures more precise delivery of radiation dose.