Objective To compare photon-modulated radiation therapy(IMRT)and proton-modulated radia-tion therapy(IMPT)after breast-conserving surgery for left breast cancer under deep inspiratory breath-hold(DIBH)dosimetry differences.Methods A total of 7 female patients who received postoperative radiotherapy for left breast cancer in DIBH mode from November 2020 to May 2020 at the First Affiliated Hospital of USTC(Hefei Ion Medical Cen-ter)were selected.The planing target volume(PTV)was prescribed at 50 Gy(5 weeks,25 times),and the local dose was increased to PTVboost:60 Gy for areas with high imaging(including functional imaging)suspicion of residual or re-current lesions.The IMRT plan was designed on the Varian Eclipse 15.5 plan system and the IMPT plan was designed on the Eclipse 16.1 plan system,respectively.The dose distribution,conformal index(CI),homogeneity index(HI),bi-lateral lungs,healthy breast gland(right breast),heart and left anterior descending coronary artery(LAD)of the two groups of planned targets were analyzed statistically.Results Proton versus photon radiation,the maximum dose(Dmax)of PTV(P=0.389)and the mean dose(Dmean)(P=0.044),Dmax of PTVboost(P=0.226)and Dmean(P=0.018),CI(P=0.035)and HI(P=0.419),Dmax of affected lung(left lung)(P=0.153),Dmax of healthy lung(right lung)(P=0.318)and Dmean(P=0.046),Dmax of heart(P=0.014),Dmax of LAD(P=0.025)and Dmax of healthy side breast(right breast)Dmax(P=0.097)were all the same as those in the photon program.However,the left lung Dmean(P＜0.01),V5(P＜0.001),V20(P＜0.001)of the affected side(left lung)of the proton program;Dmean of heart(P＜0.001);Dmean of LAD(P＜0.001);Dmean of healthy side breast(right breast)(P=0.010)were significantly lower than those of the photon program.Conclusions Both proton and photon programs after breast-conserving surgery for left breast cancer under DIBH meet clinical requirements.However,proton radiotherapy can significantly reduce the irradia-tion dose to the heart and its subunits,the affected lung and the healthy breast.
Breast neoplasmsProton therapyPhotons therapyRadiotherapy dosage
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