Objective To investigate the impacts of planning target volume (VPTV),maximal heart distance (MHD),central lung distance (CLD),and cardiothoracic ratio (CTR) on intensity-modulated radiotherapy (IMRT) after breast-conserving surgery for breast cancer.Methods Forty-eight patients with breast cancer (31 with left-sided breast cancer and 17 with right-sided breast cancer) who received whole-breast IMRT after breast-conserving surgery in our hospital from 2016 to 2017 were enrolled as subjects.The prescribed radiation dose tor PTV was 50 Gy in 25 fractions.In IMRT planning for each patient,the objective function was optimized using physical parameters and the equivalent uniform dose.The relationship of influencing factors with dose-volume histogram,conformal index (CI),and homogeneity index (HI) for organ at risk was predicted using univariate and multivariate linear regression analyses.Results CTR and VPTV were independent influencing factors for CI in patients with left-sided breast cancer (R2=0.56,P=0.04;R2 =0.56,P=0.00).CLD was an independent influencing factor for HI in patients with left-sided breast cancer (R2=0.17,P=0.023).VPTV was an independent influencing factor for CI in patients with right-sided breast cancer (R2 =0.48,P=0.00).MHD and CTR were predictors for VHeart30 of the heart.MHD and CLD were predictors for DmaxHeart of the heart.The prediction formulae for left-sided breast cancer were CI=0.38+0.32CTR and HI=1.06+0.02CLD.CI was 0.48 at the right side.At the left side,Vlung20=12.68+3.18CLD,Vlung10=18.78+4.3CLD,Vlung5=26.2+5.2CLD,and Dmeanlung=686.7+210.ICLD.For the heart,VHeart30=-13.65+30.5CTR+1.9MHD and DmaxHeart =5 140.1 +248.9MHD-195.6CLD.There was no correlation of patient's heart volume with MHD,VHeart10,VHeart5,DmeanHeart,or DmaxHeart.There was no correlation of whole lung volume with CLD,Vlung20,Vlung10,Vlung5,or Dmeanlung.The mean values of CI and HI were 0.63± 0.06 (0.46-0.72) and 1.09± 0.02 (1.07-1.14-) in radiotherapy plans for left-sided breast cancer,and 0.65± 0.08 (0.4-8-0.76) and 1.09± 0.04 (1.03-1.18) in radiotherapy plans for right-sided breast cancer,respectively.Conclusions CTR,CLD,and MHD can predict the rationality of each parameter in IMRT planning for left-sided breast cancer rather than right-sided breast cancer.The obtained formulae can help physicians choose the optimal setting mode for radiation field and improve the quality of treatment plans.

Radiotherapy is necessary for 70％ of malignant tumor patients. Local recurrence and metastasis are primary failure models, where radioresistance is one of important factors. It is critical to establish radioresistant tumor cell lines for understanding the mechanism of radioresistance. According to single radiation, fractioned radiation and the compound radiation method, four representative radiation models are classified: conventional radiation, repeated radiation, gradient radiation and other radiation. These different radiation models have difference in total dose and radiation model as well as the biological characteristics. Superior to other three models, the gradient fractioned irradiation model increase fractioned doses gradually along with the enhancement of radioresistance, which favorably balances the fractioned doses and the time of irradiated cells approaching to exponential growth phase. Clinically relevant radioresistant cell line ( CRR) with a genotype in consistent with its parental cells is an important research direction on tumor radioresistance.