Bolus厚度和使用次数对乳腺癌根治术后调强放疗皮肤剂量影响

Effects of bolus thickness and use frequency on skin dose in postmastectomy intensity-modulated radiotherapy

目的探讨Bolus厚度和使用次数对乳腺癌根治术后调强放疗皮肤剂量影响。方法选取20例乳腺癌根治术后患者固定野调强放疗计划进行回顾性分析,单独使用0.5 cm或1 cm厚Bolus次数为5 F、10 F、15 F、20 F、25 F和混合使用0.5 cm和1 cm厚Bolus来研究放疗计划靶区均匀性指数(homogeneity index,HI)、适形度指数(conformity index,CI)及皮肤剂量D_(max)、D_(mean)、D_(min);拟合出皮肤剂量与Bolus使用次数的关系式。结果随着Bolus使用次数增加,皮肤剂量增加,靶区热点减小、低剂量体积降低。不同Bolus使用次数1 cm厚Bolus比0.5 cm厚Bolus靶区均匀性均更好(P <0.05),且随着Bolus使用次数增加,HI逐渐降低。0.5 cm和1 cm厚Bolus靶区CI随着Bolus使用次数增加先增大后减小,在15 F附近最大,仅在20 F和25 F 2种厚度Bolus的CI结果具有统计学意义(P <0.05)。0.5 cm厚Bolus皮肤D_(max)和Dmean高于1 cm厚Bolus(P <0.05)。皮肤剂量D与Bolus使用次数F成D=A×F+B×F2+C的关系式。使用0.5 cm厚Bolus 6次外加使用1 cm次8次(0.5 cm 6 F+1 cm 8 F)皮肤D_(max)、HI结果介于0.5 cm 15 F和1 cm 15 F次之间(P <0.05)。结论在乳腺癌根治术后固定野调强放疗中,可以根据Bolus使用次数计算皮肤剂量。提供了一种可以混合使用Bolus的可能性,比单独使用0.5 cm或1 cm Bolus更合适。

Objective To investigate the effects of bolus thickness and use frequency on skin dose in postmastectomy intensity-modulated radiotherapy.Methods We retrospectively reviewed 20 cases receiving postmastectomy fixed-field intensity-modulated radiotherapy,to analyze the homogeneity index(HI)and conformity index(CI)of the target volume and the skin dose(D_(max),D_(mean),and D_(min))of radiotherapy plans with 0.5 cm-thick bolus or 1 cm-thick bolus alone at a use frequency of 5 F,10 F,15 F,20 F,and 25 F versus a combination of 0.5 cm and 1 cm-thick bolus,and fit the relationship between skin dose and bolus use frequency.Results As the bolus use frequency increased,the skin dose increased,the hot spot of the target volume decreased,and the low-dose volume decreased.The HI of the target volume with the 1 cm bolus was better than that with the 0.5 cm bolus at all use frequencies(P<0.05),and HI decreased with the increase of bolus use frequency.For both 0.5 cm and 1 cm bolus,the CI of the target volume increased initially and then decreased,reaching the maximum value at a frequency of around 15 F;the CI showed significant differences only at 20 F and 25 F between the two types of bolus(P<0.05).The skin D_(max) and Dmean were significant higher with the 0.5 cm bolus than with the 1 cm bolus(P<0.05).The equation for the relationship between skin dose(D)and bolus use frequency(F)was D=A×F+B×F^(2)+C.The D_(max) and HI with the combination of 0.5 cm bolus(6 F)plus 1 cm bolus(8 F)fell between those with the 0.5 cm bolus(15 F)and those with the 1 cm bolus(15 F)(P<0.05).Conclusion In postmastectomy fixed-field intensity-modulated radiotherapy,skin dose can be calculated based on bolus use frequency.Mixed use of bolus may be more suitable than use of 0.5 cm bolus or 1 cm bolus alone.