Analysis of Dose-Distribution in Left-Lung and Heart as Increasing the Number of Beams in Left-Sided Breast Irradiation

Breast cancer has been a leading malignancy in women across the globe. In breast conserving treatment, radiation therapy plays an important role. This is clinically approved that breast conserving surgery followed by adjuvant radiation therapy produces as the same survival rate as radical breast RT. The aim of this study was to find out suitable number of IMRT fields to treat left-sided breast cancer and analyze the effects of increasing the number of fields in IMRT plans.We selected 105 patients retrospectively for this study diagnosed with left-sided breast cancer of age ranging from 33 to 74 years.  There were 52 cases of chest wall (CW) irradiation including SCF, 20 cases of BCS and 33 cases were of CW including supra-clavicular fossa (SCF) and internal mammary lymph nodes (IMLN).Our main objective was to analyze dose-distribution of left lung. Monitor Units (MUs) were also recorded and found almost same in these three modalities ranging from 1200 to 2000. The mean value of V20Gy(cc) in 11-bIMRT technique was found less by 8-17cc as compared to 7-and 9-bIMRT technique. It was observed that 11-bIMRT technique yielded slightly better outcomes in terms of V20Gy(cc). The technique 7-bIMRT gives slightly better result in controlling low-dose volume of underlying lung and heart. As the number of IMRT beams increases, it translates into better outcomes in terms of reducing high-dose volume as well as mean-dose of left lung. So, it is prudent to use ‘N’ number of IMRT fields such as 7≤ N ≤11 in left breast RT.