Dosimetric comparison between dIMRT and VMAT for bilateral breast cancer

Abstract

Objective To compare the dosimetric difference of target and organs-at-risk between intensity-modulated radiotherapy (dIMRT) and volumetric modulated arc therapy (VMAT) for bilateral breast cancer, so as to discuss the clinical feasibility of radiotherapy for bilateral breast cancer.

Methods The clinical data of 18 patients receiving radical or modified radical mastectomy for confirmed bilateral breast cancer were enrolled in this study. dIMRT plans and VMAT plans were designed for each patient, and discuss the dosimetric data of two radiotherapy plans.

Results Both the two plans satisfied the prescription. In terms of the homogeneity index, VMAT plans (0.09 ± 0.02) were superior to dIMRT plans (0.11 ± 0.1, P < 0.05). In terms of the conformity index,VMAT plans (0.82 ± 0.52) were superior to dIMRT plans (0.71 ± 0,51, P < 0.05). Furthermore, VMAT plans (0.98 ± 0.06) were superior to dIMRT plans (1.24 ± 0.08, P < 0.05) in the dose gradient index. The V ₁₀, V ₂₀, V ₃₀ and D _mean of lungs in VMAT plans (39.07 ± 4.92, 22.19 ± 4.36, 12.81 ± 4.71, 1 309.03 ± 135.55) were higher than those in dIMRT plans (30.34 ± 4.26, 17.56 ± 4.31, 6.77 ± 3.93, 1 201.39 ± 166.77, P < 0.05). Meanwhile, the V ₅ of lungs in VMAT plans (63.36 ± 9.02) was higher than that in dIMRT plans (58.01 ± 7.17, P > 0.05). However, the V ₅, V ₃₀ and D _mean of heart in VMAT plans (51.98 ± 3.60, 3.78 ± 1.76, 885.89 ± 59.84) were lower than those in dIMRT plans (77.16 ± 12.11, 5.22 ± 2.85, 1 036.96 ± 151.46, P < 0.05). The D _max of spinal cord in VMAT plans (2 150.42 ± 136.19) was significantly lower than that in dIMRT plans (3 008.23 ± 304.15, P < 0.05), Monitor units in VMAT plans (792.61 ± 62.53) was significantly lower than that in dIMRT plans (3 225.33 ± 498.66, P < 0.05).

Conclusion Although VMAT has many advantages: achieves better homogeneity index and conformity index of target areas, reduces the irradiation dose of organs-at-risk, especially, the irradiation dose of heart and spinal cord is significantly reduced, however, it increases the irradiation dose of lungs. To reduce the recurrence of grade ≥ 2 radiation pneumonia, dIMRT should be better considered in the application of radiotherapy for bilateral breast cancer.

Abstract

摘要： 目的 对比双侧乳腺癌术后放疗采用动态调强技术 (dIMRT) 和容积旋转调强技术 (VMAT) 时靶区和危及器官 的剂量学差异, 探索临床应用的可行性。 方法 选择 18 例双侧乳腺癌术后行全乳放疗的患者, 分别设计 dIMRT 和 VMAT 两组计划, 比较分析剂量学参数。 结果 两种治疗技术均能满足处方要求, 其中 VMAT 组的靶区均匀性指数 (0.09 ± 0.02) 优于 dIMRT 组 (0.11 ± 0.01), 适形度指数 (0.82 ± 0.52) 优于 dIMRT 组 (0.71 ± 0.51), 剂量梯度指数 (0.98 ± 0.06) 优于 dIMRT 组 (1.24 ± 0.08), 差异均具有统计学意义 ( P < 0.05); VMAT 组双肺的 V ₁₀、 V ₂₀、 V ₃₀ 和 D _mean (39.07 ± 4.92, 22.19 ± 4.36, 12.81 ± 4.71, 1 309.03 ± 135.55) 均高于 dIMRT 组 (30.34 ± 4.26, 17.56 ± 4.31, 6.77 ± 3.93, 1 201.39 ± 166.77), 差异具有统计学意义 ( P < 0.05), VMAT 组双肺的 V ₅ (63.36 ± 9.02) 高于 dIMRT (58.01 ± 7.17), 差异无统计学 意义 ( P > 0.05); VMAT 组心脏的 V ₅、 V ₃₀ 和 D _mean (51.98 ± 3.60, 3.78 ± 1.76, 885.89 ± 59.84) 均明显低于 dIMRT 组 (77.16 ± 12.11, 5.22 ± 2.85, 1 036.96 ± 151.46), 差异具有统计学意义 ( P < 0.05); VMAT 组脊髓的 D _max (2150.42 ± 136.19) 较 dIMRT 组 (3008.23 ± 304.15) 减少, 差异具有统计学意义 ( P < 0.05); VMAT 组机器跳数 (792.61 ± 62.53) 较 dIMRT 组 (3225.33 ±498.66)明显减少, 差异具有统计学意义 ( P < 0.05)。 结论 VMAT 技术可使靶区剂量分布拥有 更好的均匀性和适形性, 且拥有更少的高剂量区域。在危及器官受量方面, VMAT 技术可显著降低心脏和脊髓受量, 但双肺的受照剂量增加。在临床应用中, 选择 dIMRT 技术更为合适, 可降低发生 ≥2 级症状性 RP 的风险。