Impacts of Increasing the Number of IMRT Beams on Heart’s Dose Distribution in Left Breast Irradiation: Dosimetric Study

Introduction: The main objective of this study was to assess the impacts of an increasing the number of IMRT beams on cardiac dose distribution in left-sided breast irradiation so that we can reduce the heart’s mean dose  up to clinically acceptable level.Material and Methods: For this study ۱۰۷ female patients, diagnosed with left-sided breast cancer were selected retrospectively. In ۱۰۷ patients, there were ۵۲ patients of chest wall irradiation including supra-clavicular fossa, while ۲۲ patients were of breast-conserving surgery excluding supra-clavicular fossa and internal mammary lymph nodes, and ۳۳ patients were of chest wall irradiation including internal mammary lymph nodes and supra-clavicular fossa. Exclusion criteria were previous history of left-sided breast radiation therapy, uncommon fractionated dose delivered in past, and indication of palliative radiation therapy. Intensity modulated radiotherapy plans were generated using ۷, ۹ and۱۱ beams for each patient and the prescribed dose was ۴۰.۰۵ Gy in ۱۵ fractions (۲.۶۷ Gy /fraction) for the targets.Results: Heart: V۵Gy(cc): This was a low-dose volume of our study in which the ۱۱-bIMRT technique yielded better result as compared to ۹- and ۷-bIMRT. Maximum and minimum values of V۵ were found ۵۳۹.۶۰cc in ۹-bIMRT and ۱۴۱.۳۲cc in ۱۱-bIMRT techniques respectively.V۲۵Gy(cc): The maximum value of V۲۵Gy was found ۴۱.۷۳cc in ۷-bIMRT technique, while the lowest value was ۰.۲۹cc in ۱۱-bIMRT. The IMRT technique with ۱۱ beams showed comparatively better result on this parameter as well as ۳-۵cc volume of V۲۵Gy was spared. Mean dose (Gy): Maximum value of mean dose was found ۸.۵۱Gy in ۷-bIMRT while it was ۶.۵۳Gy in ۱۱-bIMRT technique.   Conclusion: The study indicates that increasing the number of IMRT beams reduces heart’s high-dose volume and improves the quality of treatment plans. It is judicious to use ۱۱-bIMRT technique in left-sided breast irradiation as it produces clinically acceptable mean heart dose.