Dosimetric comparison between dIMRT and VMAT for bilateral breast cancer / 中国辐射卫生

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 ± 0.01, 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 V10、V20、V30 and Dmean of lungs in VMAT plans (39.07 ± 4.92，22.19 ± 4.36，12.81 ± 4.71，1309.03 ± 135.55) were higher than those in dIMRT plans (30.34 ± 4.26，17.56 ± 4.31，6.77 ± 3.93，1201.39 ± 166.77, P < 0.05).Meanwhile, the V5 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 V5、V30 and Dmean 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 ± 2.85，1036.96 ± 151.46, P < 0.05). The Dmax of spinal cord in VMAT plans (2150.42 ± 136.19) was significantly lower than that in dIMRT plans (3008.23 ± 304.15, P < 0.05). Monitor units in VMAT plans（792.61 ± 62.53）was significantly lower than that in dIMRT plans (3225.33 ± 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.