A Dosimetric Comparison.between Hypofractionated Whole Breast Irradiation And Conventionally Fraction Whole-breast Irradiation After Breast-conserving Surgery For Early Stage Left Breast Cancer

Background and purpose:This study was to compare the doses of conventionally fraction whole-breast irradiation and hypofractionated whole breast irradiation target areas and sub-structures of the heart after breast-conserving surgery for early left breast cancer.The dose parameters were quantified by biodosimetry and two different radiotherapy treatments were compared.The difference in biological effects after radiotherapy in various parts of the heart.Materials and methods: Ten patients with radiotherapy after breast-conserving surgery in the left breast cancer from June 2018 to December 2018 in Jiangxi Provincial Cancer Hospital were collected.After enhanced positioning scan,the Pinnacle 3D treatment planning system delineates the target area and normal tissues and organs such as heart,lung,contralateral breast and spinal cord.the heart substructure including the left anterior descending and left ventricle.Two radiotherapy plans were developed using intensity-modulated radiotherapy: CFWBI prescribed to 50Gy/25 fractions and HFWBI prescribed to 42.56 Gy/16 fractions.Dose parameters of heart,LAD,LV,lung and right breast were calculated under HFWBI using biological effective dose.The dose-volume relationship of the heart and its substructures was evaluated in two different radiotherapy modes.Results:(1)After adjusting for Equivalent Dose in 2 Gy fractions(EQD2),and comparing HFWBI with CFWBI,the maximum doses of the heart,left ventricle and left lung were smaller,which the difference was statistically significant(P<0.05),and the maximum dose of the left anterior descending artery was slightly lower,no statistical significance.(2)Compared with CFWBI,HFWBI reduced the average dose of heart and left ventricle by 27 cGy and 67 cGy,the difference was not statistically significant,and the mean left anterior descending and left lung doses were also reduced(2367 cGy VS 2291 cGy,P=0.037 and 1089 cGy VS 1005 cGy,P = 0.000),the difference was statistically significant.(3)The HFWBI reduced the radiation volume of the heart V5,V10,V20,V30 and V40,the difference was statistically significant(P<0.05).It reduced the radiation volume of left ventricularV5 and V20,thedifference was statistically significant(P<0.05).There also reduced the radiation volume of he left lung V5,V10,V20,V30 and V40,the difference was statistically significant(P<0.05).(4)The coverage of the two radiotherapy regimens was satisfactory.The maximum dose and average dose ofHFWBI were lower than those of CFWBI,and the difference was statistically significant(P<0.05).Conclusion: This study investigated the two methods of CFWBI and HFWBI after breast-conserving surgery for early stage left breast cancer by dosimetry.Both radiotherapy modes target coverage can meet clinical requirements.Compared to CFWBI,HFWBI showed a significant reduction in radiation dose for the the heart,LAD,LV and the left lung.HFWBI does not add extra long-term radiotherapy toxicity to the heart and lungs.