Dosimetric Comparison of the Lung Dose on the Affected Side in Radiotherapy after Breast Cancer Breast-Conserving Therapy Based on Two Subfield Optimization Methods in Monaco Planning System

Objective — To conduct comparison of the quantity difference of different segmentation optimization methods in Monaco planning system on the affected lung in radiotherapy after breast cancer breast-conserving therapy. Methods — 10 cases with breast cancer after breast-conserving surgery were selected with the prescription dose of 50GY/25F. In each case, volume modulated arc therapy (VMAT) based double arc distribution mode was adopted, and the same optimization parameters and functions were set accordingly. After completion of flux optimization, automatic weight optimization method and manual weight optimization method were adopted for optimization respectively. When the similar dose distribution of the target volume was obtained and the dose of the organ at risk (OAR) was satisfied, the dose of the affected lung obtained by the two optimization methods was compared. Results — When similar target coverage and other organs at risk met the prescribed conditions, the affected lung received by the manual weight optimization method was significantly lower than that by the automatic weight optimization method, and the results were statistically significant. Conclusion — The manual weight optimization method used in VMAT program after breast conserving surgery can effectively reduce the lung volume on the affected side and the probability of radiation pneumonia can be reduced.