左侧乳腺癌根治术后两种常用放疗计划剂量学比较

Dosimetric comparison of two common intensity modulated radiotherapy for left breast cancer receiving post-mastectomy

目的评估左侧乳腺癌根治术后两种常用调强放疗方法的靶区及其周围正常组织受照剂量的差异,为术后放疗临床选择提供理论依据。方法选取2014-01-01-2014-04-28江西省肿瘤医院15例左侧乳腺癌根治术后患者,经CT扫描后将图像传至Pinnacle3治疗计划系统中进行靶区勾画。每位患者分别设计两种不同角度的7野(Ⅰ)和6野(Ⅱ)共面适形调强放疗(intensity modulated radiation therapy,IMRT)计划。两种设野方法的机架角度分别为Ⅰ:300°,330°,0°,30°,60°,90°,140°;Ⅱ:300°,315°,350°,115°,130°,140°。在满足PTV达到95%处方剂量的前提下,采用剂量体积直方图评价两种调强方法的靶区和周围正常组织照射剂量和靶区适形指数(conformity index,CI)及剂量均匀性指数(homogeneity index,HI)。结果计划Ⅰ和Ⅱ组的PTVmean分别为(51.39±3.43)和(52.46±0.31)Gy,z=-0.713,P=0.476;HI分别为1.08±0.01和1.07±0.01,z=-1.742,P=0.081;CI分别为0.73±0.05和0.65±0.02,z=-2.936,P=0.003。Ⅱ组心脏V5接受的受照体积为60.43±11.04,明显小于Ⅰ组的76.84±14.49,z=-2.402,P=0.016;Ⅱ组心脏V10为25.15±8.56,明显小于Ⅰ组的36.38±20.00,z=-2.046,P=0.041;Ⅱ组心脏V40为1.24±1.15,明显小于Ⅰ组的2.59±1.32,z=-2.491,P=0.013。Ⅱ组左肺受照平均剂量Dmean为13.85±0.81,较计划Ⅰ组的13.04±0.79略高,z=-2.936,P=0.003;Ⅱ组左肺接受低剂量照射体积V5为58.03±10.51,明显小于Ⅰ组的71.43±16.09,z=-2.936,P=0.003。Ⅱ组右肺接受的照射平均剂量Dmean为1.47±0.86,低于Ⅰ组的5.23±0.83,z=-2.936,P=0.003。Ⅱ组右侧乳腺接受的照射平均剂量Dmean为2.04±0.54,明显低于Ⅰ组的5.27±0.78,z=-2.937,P=0.003;V5为11.45±4.34,明显小于Ⅰ组的46.69±6.25,z=-2.937,P=0.003。Ⅱ组甲状腺最大剂量为42.35±4.15,高于Ⅰ组的38.77±5.26,差异有统计学意义,z=-2.937,P<0.05。结论两种调强方法的靶区照射剂量分布基本相当,但是在对心脏、健侧乳腺及右肺等危机器官的保护上方法Ⅱ明显优于Ⅰ。6野切线射野方式对于降低正常组织器官的照射量具有重要意义,值得在临床推广应用。

OBJECTIVE To evaluate the dose distribution of target volume and normal tissues of two commonly used intensity modulated radiotherapy for left breast cancer receiving post-mastectomy.METHODS In randomly selected15 patients with left breast cancer receiving post-mastectomy,the CT images of patients were transmitted to the pinnacle3 treatment planning system to contour the tumor target.Treatment planning of IMRT 7coplanar fields（Ⅰ）and 6coplanar fields（Ⅱ）were worked out by computer working station,respectively.Beam angles of methodⅠwere：300°,330°,0°,30°,60°,90°,140°.Beam angles ofⅡwere：300°,315°,350°,115°,130°,140°.Meeting 95%PTV received the prescribed dose,the dose distributions of plan target volume and normal tissues,conformal index（CI）and heterogeneous index（HI）were evaluated in terms of the dose volume histogram（DVH）.RESULTS The mean dose of PTV in plan Ⅰ was（51.39±3.43）Gy and in planⅡ was（52.46±0.31）Gy（z=-0.713,P=0.476）,The HI in planⅠ was 1.08±0.01 and in plan Ⅱ was 1.07±0.01（z=-1.742,P=0.081）.The CI in plan Ⅰ was 0.73±0.05 and in plan Ⅱ was 0.65±0.02（z=-2.936,P=0.003）.The dose received of heart in planⅠ was much bigger thanⅡ at the V5（76.84±14.49 vs60.43±11.04,z=-2.402,P=0.016）,V10（36.38±20.00 vs 25.15±8.56,z=-2.046,P=0.041）,V40（2.59±1.32 vs 1.24±1.15,z=-2.491,P=0.013）.The mean dose of left lung in plan Ⅱ was bigger than that in plan Ⅰ（13.85±0.81 vs 13.04±0.79,z=-2.936,P=0.003）.The volume at V5 in planⅡ was much smaller than that in planⅠ（58.03±10.51 vs 71.43±16.09,z=-2.402,P=0.016）.The mean dose（1.47±0.86 vs 5.23±0.83,z=-2.936,P=0.003）and V5（1.52±1.81 vs 39.72±8.80,z=-2.805,P=0.005）of right lung in plan Ⅱ were significantly lower than that in planⅠ.The mean dose（2.04±0.54 vs 5.27±0.78,z=-2.937,P=0.003）and V5（11.45±4.34 vs 46.69±6.25,z=-2.937,P=0.003）of right breast received in plan Ⅱ were lower than that in plan Ⅰ.The max dose of thyroid（42.35±4.15 vs 38.77±5.26,z=-2.937,P=0.003）in planⅡ was bigger than in planⅠ.CONCLUSIONS The PTV received dose is insignificantly different in the two kinds IMRT methods.In protection the heart,right lung and right breast or other important critic organs method Ⅱis obviously much better than plan Ⅰ.Comparing with plan Ⅰ,planⅡ was the optimal plan for clinical practice.