乳腺癌保乳术后两野与多野动态调强的剂量学研究

目的 比较早期乳腺癌保乳术后切线2野动态调强与非共面多野调强放疗治疗靶区和危及器官的剂量学差异。方法 选取40例接受保乳术后放疗的左侧乳腺癌患者，在同一患者CT影像上，利用相同优化条件分别进行切线2野和非共面3、4、5野4种调强治疗计划设计。比较4种计划的靶区剂量分布、心脏、左肺及右侧乳腺受照剂量和体积，以及机器跳数的差异。结果 非共面4、5野调强计划适形度指数（CI）和均匀性指数（HI）均优于切线2野调强计划（P<0.05），临床靶区（PTV）最大剂量（D_max）小于2野调强计划（P<0.05），PTV最小剂量（D_min）大于2野调强计划（P<0.05）。3野与2野计划间无明显差异。4种计划的右乳接受5 Gy照射的百分体积（V₅）、心脏接受30 Gy照射的百分体积（V₃₀）及平均剂量（D_mean）、左肺接受20和5 Gy照射的百分体积（V₂₀、V₅）、平均剂量（D_mean）无明显差异，而机器跳数间差异有统计学意义（F=25.63，P<0.05），2野调强跳数最少，5野最多。结论 保乳术后非共面4、5野调强计划与切线2野调强计划相比，靶区剂量分布更好，不明显增加正常组织、器官的受照射剂量，但机器跳数明显增加。

Dosimetric study of tangential and multi-fields applied in the dynamic intensity modulated radiotherapy plans for breast cancer patients after breast-conserving surgery

Objective To compare the dosimetric differences of target and organs at risk (OAR) induced by the tangential and non-coplanar multi-fields used in the dynamic intensity modulated radiotherapy (IMRT) plans for breast cancer patients after breast-conserving surgery. Methods Forty patients with early-stage left breast cancer after breast-conserving surgery were included. Based on the CT anatomy of the same patient, dynamic IMRT treatment plans using two tangential fields, 3, 4 and 5 non-coplanar fields were designed respectively utilizing the same optimization objects. The plans were compared by means of target dose distribution, the doses and irradiated volumes of heat, left lung, right breast, and total monitor units (MUs). Results The conformal index (CI) and homogeneity index (HI) of planning target volume (PTV) in the plans using 4 and 5 fields were better than that using 2 fields (P<0.05). Maximum doses (D_max) in PTV were significantly lower in the plans of 4 and 5 fields than of 2 fields (P<0.05). Yet the plans of 4 and 5 fields generated significant higher minimum doses (D_min) in PTV than that of 2 fields (P<0.05). No significant difference was observed between plans of 2 or 3 fields. Across the four plans, the differences of right breast V₅ (relative volume acquired at least 5 Gy of dose), heart V₃₀, heart mean dose (D_mean), left lung V₂₀, V₅ and D_mean were not significant. Yet the disparities of total MUs were statistically significant (F=25.63, P<0.05). The least MUs were used by the 2 fields and the most MUs were observed in the 5-field plans. Conclusions Comparing with IMRT plans of 2 fields, using 4 or 5 non-coplanar fields can improve the target dose distribution without increasing OAR doses. As a tradeoff, more MUs are needed for multi-fields plans.