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

Introduction: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.Material and Methods:We selected ۱۰۵ patients retrospectively for this study diagnosed with left-sided breast cancer of age ranging from ۳۳ to ۷۴ years.  There were ۵۲ cases of chest wall (CW) irradiation including SCF, ۲۰ cases of BCS and ۳۳ cases were of CW including supra-clavicular fossa (SCF) and internal mammary lymph nodes (IMLN).Results: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 ۱۲۰۰ to ۲۰۰۰. The mean value of V۲۰Gy(cc) in ۱۱-bIMRT technique was found less by ۸-۱۷cc as compared to ۷-and ۹-bIMRT technique. It was observed that ۱۱-bIMRT technique yielded slightly better outcomes in terms of V۲۰Gy(cc).Conclusion: The technique ۷-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 ۷≤ N ≤۱۱ in left breast RT.

Keywords:

Breast Cancer , Beam , Irradiation , IMRT , planning target volume