A Dosimetric Research Of Lung Dose Sparing Effect By Deep Inspiration Breath Hold In Radiotherapy For Left-sided Breast Cancer

Background and aims: Radiotherapy serving as a routine treatment for breast cancer patients after breast-conserving surgery and part of post mastectomy patients,can improve local control rate,reduce the risk of long-term death,and achieve the better overall survival.However,radiotherapy eradicates the tumor,while it damages the surrounding normal tissues at the same time.Radiation induced lung injury is one of the complications of chest radiotherapy,its occurrence is closely related to the irradiated dose and volume of both lungs.Reducing the irradiated heart and lung dose to the maximum during breast cancer radiotherapy,can effectively reduce the occurrence of radiation induced heart and lung injury,further improve the quality of life and survival of breast cancer patients.Deep inspiration breath hold is a competent dose sparing technique during left-sided breast cancer radiotherapy,but its dose sparing effect is ambiguous to the lungs,which is a hot topic among researchers.This research will further discuss whether deep inspiration breath hold technique can reduce lung irradiated dose compared to free breathing CT simulation,and find the beneficial patient cohort of deep inspiration breath hold,so as to reduce the occurrence of radiation induced lung injury during left-sided breast cancer radiotherapy.Materials and Methods: A total of 60 patients with left-sided breast cancer who hospitalized in the First Affiliated Hospital of Dalian Medical University,diagnosed with surgical pathology of breast invasive carcinoma and carcinoma in situ after surgery and planned to receive radiotherapy were selected.The mean age of all patients was53.10±9.41 years.All the patients were stage 0-III.Treatment plans were created on both free breathing and deep inspiration breath hold CT scans for each patient,with a prescription dose of 50Gy/25 f.The prescription dose of the post breast-conserving surgery patients was 57.5Gy/2.3Gy/25 f.The dosimetric parameters of both lungs were obtained from dose-volume histogram,including the mean lung dose,V40,V30,V20,V10 and V5 of ipsilateral lung,and V10,V5 of contralateral lung,they were further compared between two treatment plans.11 patient-related parameters were collected,including age,BMI(Body Mass Index),surgery type,radiation target range,total planning target volume,left lung volume under free breathing,the ratio of left lung volume(the volume ratio between deep inspiration breath hold and free breathing),MHD(maximum heart distance),CLD(central lung distance),MLW(midplane lung width)and HI(haller index),which were used to predict the dose sparing effect of deep inspiration breath hold to the lungs.Results:For the entire patient cohort,deep inspiration breath hold significantly improved ipsilateral lung mean dose,V30,V20,and contralateral lung V10,V5 compared with free breathing(P<0.05),the ipsilateral lung mean dose declined by 3.6%,with an absolute reduction of 40.44 c Gy.For 15 patients irradiated with affected breast ±tumor bed,no dosimetric difference was observed between two plans.The rest of the patients with regional nodal irradiation had at least two lung dose parameters been improved.Among the correlational analysis of multiple patient-related parameters and lung dose reduction between two plans,CLD under free breathing correlated positively with ipsilateral lung mean dose difference(r=0.278,P=0.031),V40 difference(r=0.261,P=0.044),V10 difference(r=0.263,P=0.042)and V5 difference(r=0.299,P=0.02),but had no correlation with ipsilateral lung V20 difference;MLW under free breathing correlated positively with ipsilateral lung mean dose difference(r=0.261,P=0.044)and V40 difference(r=0.29,P=0.025),but had no correlation with ipsilateral lung V20difference;left lung volume under free breathing correlated positively with ipsilateral lung V20 difference(r=0.255,P=0.049).Radiation target range,CLD and MLW under free breathing CT scans were included in multivariate linear regression analysis of the ipsilateral lung mean dose difference,none of the parameters could be a independent predictor of ipsilateral lung mean dose difference;the above mentioned three parameters were also included in multivariate linear regression analysis of the ipsilateral lung V40 difference,none of the parameters could be a independent predictor of ipsilateral lung V40 difference.Conclusions:1.Reduction in lung dose can be achieved for left-sided breast cancer patients with regional nodal irradiation under deep inspiration breath hold radiotherapy,but the dose sparing effect is kind of limited.2.CLD and MLW measured in axial CT scans under free breathing can be used to predict the extent of lung dose improvement: the bigger CLD or MLW,the better the lung dose sparing.3.As the patient-related parameters CLD and MLW,both been excluded from the multivariate analysis,they can’t act as independent predictors of the lung dose sparing extent of deep inspiration breath hold.4.The above mentioned conclusions are limited by the insufficient sample size of this research,the patient-related parameters able to independently predict the lung dose sparing effect of deep inspiration breath hold remain further investigations in larger patient cohorts.