Application Of High-Dose-Rate Volume Modulation And Robustness Optimization In Postoperative Radiotherapy For Breast Cancer

The use of conventional accelerators to treat breast cancer patients takes a long time to treat,which will increase the patient’s second cancer probability and discomfort.At the same time,Respiratory movement during the actual treatment process will lead to the risk of off-target chest targets,the actual target area received insufficient radiation dose.In order to solve these two problems,this study introduces a high-dose rate mode and uses a robust optimization module in combination.（1）Randomly select 20 patients undergoing left breast-conserving breast cancer surgery and 21 patients undergoing adjuvant radiotherapy after Left Postmastectomy,A total of 82 sets of plans are designed on the Ray Station planning system with and without Flatten Filter Free mode.Evaluate the difference in planned dosimetry between the two groups.（2）On the basis of selecting the FFF mode as the breast cancer radiotherapy technology,combined with the robust optimization module.Randomly select 20 patients after breast-conserving surgery and 21 patients after modified radical surgery.By moving the center point of the radiation field to simulate the movement of the internal chest wall target area caused by respiratory movement,compare the dosimetry characteristics of a total of 164 plans before and after the move.The results showed（1）In terms of OAR protection,the D_mean,V₃₀,V₂₀and V₅of the affected lung and the whole lung in the FFF mode group of the two diseases are lower than those in the FF mode group,and the differences are statistically significant（P<0.001）;For breast-conserving surgery,the radiation dose parameters of the contralateral lung,heart,normal tissue and spinal cord in FFF mode are significantly lower than those in FF mode（P<0.001）,the MU in FFF mode is higher than the FF mode（P<0.001）,but the total beam time of the FFF mode is only 90.00%of the FF mode（P<0.001）;For Postmastectomy,only the exposure dose to the heart and spinal cord of the FFF mode was significantly lower than that of the FF mode（P=0.001）,and there was no statistical difference between the contralateral lung and the normal tissue,the MU in FFF mode is 1.25 times that of FF mode,which is statistically different（P=0.004）,but the beam time is only 83.15%of FF mode.（2）In the case of the chest wall target area shifted out,for patients after breast-conserving surgery,the PTV with robust optimization D_98%,D_95%and D_2%are statistically different from the PTV without robust optimization（P<0.05）,PTV-T D95%doses were 5676.89±70.38 c Gy and 4895.62±289.17c Gy（P<0.001）;The V₅₀ of the CTV with robust optimization increased by 21.69%compared with the plan without robust optimization（P<0.001）;And CI of PTV is higher than the plan without robust optimization（P<0.001）.For patients after Postmastectomy,the PTV D_98%,D_95%,D_2%,and CI of the treatment plan with robust optimization were higher than those without robust optimization,and there was a statistical difference（P<0.05）.The HI（PTV）was less than the plan without robust optimization（P<0.001）.V₅₀（PTV-CHEST）was significantly higher than the plan without robust optimization（P<0.001）.V₅₀（CTV）was significantly higher than the plan without robust optimization（P<0.001）.So clear that（1）FFF high-dose-rate mode is more suitable as an adjuvant radiotherapy technique after breast-conserving surgery and Postmastectomy than FF conventional dose-rate mode.（2）the introduction of a robust optimization module based on the use of a high-dose rate model can effectively reduce the risk of missed targets due to respiratory movements.In clinical practice,the use of robust optimization combined with FFF mode can be considered as the first choice for planning postoperative radiotherapy for breast cancer.