左侧乳腺癌根治术后调强放疗中剂量累加的研究

Study on dose accumulation in IMRT for left breast cancer patients after radical mastectomy

目的通过形变配准及刚性配准进行左侧乳腺癌放疗中靶区及危及器官剂量累加的研究,探讨二者受量的变化规律。方法回顾分析16例女性左侧乳腺癌根治术后患者,靶区包括锁上淋巴结引流区加胸壁,均采用6 MV X射线调强放疗(IMRT)。所有患者均接受定位、二程CT扫描,在定位图像(CT1)上制定放疗计划为Plan1,在二程定位图像(CT2)上制定放疗计划为Plan2。利用Velocity软件将Plan2的剂量进行刚性、形变配准到CT1剂量累加后获得Plan-rigid、Plan-deform。比较4个计划中靶区及危及器官的剂量学差异。结果CT2比CT1的CTV体积平均缩小6.64%;形变后靶区剂量均匀性指数(HI)提高23.05%,而形变后心脏、左、右肺戴斯相似系数(DSC)均低于形变前(0.94±0.01 vs.0.89±0.05、0.96±0.01 vs.0.91±0.03、0.96±0.01 vs.0.92±0.03),且差异均有统计学意义(Z=-3.208、-3.533、-3.535,P<0.05);心脏及左肺各剂量-体积指标在Plan2、Plan-rigid、Plan-deform与Plan1的组间差异均无统计学意义(P>0.05);在Plan-rigid组各剂量-体积指标均高于Plan-deform组。结论靶区及危及器官体积、剂量-体积指标变化较小的左乳癌根治术后患者在进行放疗剂量累加时,推荐使用刚性配准,且初次调强计划的剂量-体积指标可基本反映双肺及心脏的受量情况。

Objective To investigate the changes of accumulated dose in target area and organs at risk(OARs)for radiotherapy of left breast cancer by deformable and rigid image registration.Methods A total of 16 left breast cancer patients treated with 6 MV X-ray IMRT were analyzed retrospectively.All targets included the lymph node drainage area and the chest wall.All patients underwent simulation of the primary positioning and repositioning to obtain CT images.Primary and secondary treatment plans were developed using primary positioning CT(CT1)and repositioning CT(CT2),denoted as Plan1 and Plan2 respectively.The dose distribution of Plan2 was mapped to CT1 with rigid and deformable registration from CT2 to CT1 and then added to the dose distribution of Plan1 to obtain Plan-rigid and Plan-deform,respectively.The dosimetric differences between targets and the OARs of the four plans were compared.Results The CTV volume on CT2 was reduced by 6.64%from that on CT1.The homogeneity index(HI)increased by 23.05%after deformation-based accumulation.The Dice similarity coefficients(DSCs)of the heart,left lung and right lung were lower than those before deformable registration(0.94±0.01 vs.0.89±0.05,0.96±0.01 vs.0.91±0.03,and 0.96±0.01 vs.0.92±0.03,respectively),and the differences were statistically significant(Z=-3.208,-3.533,-3.535,P<0.05).There were no significant differences in dose-volume indices of heart and left lung between Plan1 with other plans(P>0.05),while the dose-volume indices in Plan-rigid were higher than that in Plan-deform.Conclusions Rigid registration is recommended in patients undergoing radical resection of left breast cancer with little change in the volume and dose-volume index of the target area and organs at risk.The dose-volume index of the initial intensity modulation plan can basically reflect the dose-volume statistics of both lungs and heart.