ABSTRACT
【Objective】 To analyze the influence of different Inc parameters in the Monaco planning system on the left breast cancer volumetric modulated arc therapy (VMAT) planning, in the hope of providing some reference for plan design. 【Methods】 Seventeen left-breast cancer patients who were receiving radical radiotherapy were selected. The plans were enrolled in the design of VMAT with the same optimization conditions but different Inc parameters in the Monaco planning system. All plans used different Inc parameters like 10°, 20°, 30°, and 40°. The results of the plan were compared. The dosimetric parameters of the PTV and the organs at risk inquired by the plan were analyzed. The SPSS software was used for calculating the differences between the VMAT plans and evaluating the quality of the plans. 【Results】 The different Inc parameters affected the dosimetric parameters D98%, D2%, D50%, V55 Gy of PTV and CI, HI (F=10.528, F=15.154, F=15.513, F=16.979, F=4.632, F=14.277, all P<0.05). The MU of the four groups significantly differed (F=4.632, P<0.05), and the difference of V10 on the ipsilateral lung was significant (F= 3.324, P<0.05), the remaining parameters in the four groups had no statistically significant difference. 【Conclusion】 For the left-breast cancer volumetric modulated arc therapy, the smaller of Inc parameter on the plan had better dose distribution and conformity index while the monitor units increased. 40° was not suitable for the breast cancer VMAT plan, and the high amount beyond the range would increase the toxic and side effects on the skin.