Dosimetric differences of different radiation modes based on Monaco in postoperative intensity modulated radiotherapy of patients with left breast-conserving surgery for breast cancer

  Objective  To investigate the effects of different radiation modes in Monaco planning system on the dosimetry of postoperative intensity modulated radiotherapy of patients with left breast-conserving surgery for breast cancer.

  Methods  Twelve patients with left breast-conserving surgery for breast cancer were selected. The Monaco planning system was used to design single-field and double-arc (1F2A), two-field and double-arc (2F2A), and dynamic multi-leaf collimator (dMLC) plans for each patient under the same optimal conditions. The target areas and organ-at-risk dosimetric parameters of the three plans were compared.

  Results  The target doses of the three plans all met the clinical requirements. In the comparison of the parameters such as radiation dose to 2% of the planned target area (D₂), radiation dose to 98% of the planned target area (D₉₈), radiation dose to 50% of the planned target area (D₅₀), conformity index (CI) and homogeneity index (HI), 1F2A plan was significantly better than 2F2A plan and dMLC plan (P < 0.05). The volumes of left lung exposed to 5 Gy dose (V₅), exposed to 10 Gy dose V₁₀, exposed to 20 Gy dose V₂₀, exposed to 30 Gy dose V₃₀ and mean dose (D_mean) of 2F2A plan were lower than those of 1F2A plan and dMLC plan, and significant between-groups differences were observed in V₅, V₁₀ and D_mean (P < 0.05). Compared with 1F2A plan, V₅, V₁₀ and D_mean of right lung, D_mean of right breast and maximum dose (D_max) of spinal cord in 2F2A plan and dMLC plan were significantly decreased (P < 0.05). Results ofV₅ and D_meanof heart, in dMLC plan were significantly lower than those of 1F2A plan and 2F2A plan (P < 0.05). The number of segments in 2F2A plan was significantly lower than that in 1F2A plan and dMLC plan (P < 0.05).

  Conclusion  All of the three plans can meet the clinical requirements, but the 2F2A plan can reduce the irradiated dose and volume of organs-at-risk. Considering the quality of the plan and the performance efficiency, it is suggested that the volume rotation intensity modulated technique with 2F2A field distribution should be used in postoperative radiotherapy of patients with left breast-conserving surgery for breast cancer.