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

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. For this study 107 female patients, diagnosed with left-sided breast cancer were selected retrospectively. In 107 patients, there were 52 patients of chest wall irradiation including supra-clavicular fossa, while 22 patients were of breast-conserving surgery excluding supra-clavicular fossa and internal mammary lymph nodes, and 33 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 7, 9 and11 beams for each patient and the prescribed dose was 40.05 Gy in 15 fractions (2.67 Gy /fraction) for the targets. Heart: V5Gy(cc): This was a low-dose volume of our study in which the 11-bIMRT technique yielded better result as compared to 9- and 7-bIMRT. Maximum and minimum values of V5 were found 539.60cc in 9-bIMRT and 141.32cc in 11-bIMRT techniques respectively.V25Gy(cc): The maximum value of V25Gy was found 41.73cc in 7-bIMRT technique, while the lowest value was 0.29cc in 11-bIMRT. The IMRT technique with 11 beams showed comparatively better result on this parameter as well as 3-5cc volume of V25Gy was spared. Mean dose (Gy): Maximum value of mean dose was found 8.51Gy in 7-bIMRT while it was 6.53Gy in 11-bIMRT technique.    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 11-bIMRT technique in left-sided breast irradiation as it produces clinically acceptable mean heart dose.