乳腺癌调强计划边界外放对靶区和皮肤剂量的影响

Effect of boundary extension for radiation fields on target volume and skin dose in breast cancer intensity modulated plan

目的比较乳腺癌调强计划射野边界外放方法在常规和动态CT图像上对靶区和皮肤剂量的影响。方法选择行乳腺癌保乳术后放射治疗的患者10例,年龄27~69岁,平均年龄46.6岁;病灶位于左侧3例,右侧7例;临床分期为T1~T2。根据患者的三维(3D)CT常规扫描,设计5野切线方向调强计划,在5野调强计划基础上分别采用不同边界外放方法(直接通量编辑和添加虚拟Bolus)设计出新的调强计划。将3种计划拷贝到同一患者四维(4D)CT动态扫描的10个时相中分别计算平均值。统计两种扫描方式(常规扫描和动态扫描)下3种计划方法的计划靶区(PTV)(V_(95))、皮肤Skin 0.3和Skin 0.5(V_(30)、V_(40)、D_(mean))体积的评价指标,通过组内和组间对比,分析两种边界外放方法对靶区和皮肤剂量的影响。结果使用单因素方差分析方法对比两种扫描方式下3种计划方法组内的评价指标变化,其中3D CT 3种计划方法各评价指标比较,差异均有统计学意义(P<0.05)。4D CT下除PTV(V_(95))在3种计划方法中差异无统计学意义(P>0.05)外,皮肤Skin 0.3和Skin 0.5(V_(30)、V_(40)、D_(mean))差异均有统计学意义(P<0.05);使用配对t检验方法对同一计划方法在两种不同扫描方式下评价指标分析,3种计划方法在组间比较中PTV(V_(95))差异有统计学意义(P<0.05),皮肤剂量指标只有在添加虚拟Bolus计划方法下,Skin 0.5(V30、V40)的组间比较,差异有统计学意义(P<0.05)。结论两种边界外放方法无论在常规还是动态CT图像上,对靶区处方剂量分布影响不大,均能满足临床治疗需求,但会增加照射野范围内乳腺的皮肤剂量,在临床应用中应评估和关注其对皮肤的损伤。

Objective To compare the effects of intensity-modulated planning field boundary extension methods on target volume and skin dose between routine and dynamic CT images in breast cancer.Methods A total of 10 patients with breast cancer performed radiotherapy after breast-conserving surgery were enrolled,which aged 27-69 years old with mean age of46.6 years old.The lesions were located on the left side in 3 cases and on the right side in 7 cases.The clinical stages of patients were T1-T2.According to three-dimensional(3D)CT routine scan of patient,the 5-field tangential intensity-modulated plan was designed,and novel plans were further designed based on the five-field intensity modulated plan by using different boundary extension methods(direct flux editing and adding virtual Bolus)respectively.The three plans were copied into 10phases of 4D CT dynamic scanning in same patient,and mean values were calculated respectively.The evaluation indexes of planning target volume(PTV)(V_(95)),Skin 0.3 and Skin 0.5(V_(30),V_(40),D_(mean))of 3 plans by 2 scanning modes were statistically analyzed,and the effects of 2 boundary extension methods on the target area and skin dose were analyzed and compared by intragroup and inter-group.Results One-way analysis of variance was used to compare changes in evaluation indexes of 3 plans under 2 scanning methods,and the differences in evaluation indexes of 3 plans 3D CT were statistically significant(P<0.05).In 3 plans,there was no significant difference in PTV(V_(95))under 4D CT(P>0.05),and there were significant differences in Skin 0.3 and Skin 0.5(V_(30),V_(40),D_(mean))(P<0.05).The paired t-test was used to analyze evaluation indexes of the same plan under 2 different scanning methods,statistically significant difference were found in PTV(V_(95))of 3 plans(P<0.05).Notably,statistically significant differences were only found inter-groups in Skin 0.5(V_(30),V_(40))under adding virtual Bolus plan(P<0.05).Conclusion It is demonstrated that on routine or dynamic CT images,the 2 boundary extension methods could meet clinical demand,which showed little effect on prescribed dose distribution in the target area.However,it will increase the breast skin dose within the irradiation field,and skin damage should be evaluated and attracted attention in clinical application.