Background: Irradiation of supra-clavicular lymph nodes (SC-LNs) is an integral part of breast cancer radiotherapy. Efforts were exerted to improve dose distribution to this area for proper coverage of target volume & to decrease radiation dose to organs at risk. Objectives: We aimed at improving the outcome of the dose homogeneity and distribution during breast radiotherapy - to allow better dose coverage of supraclavicular fossa/field (SCF) with consequent decrease of the radiation dose to normal organ at risk. Effect of variation in body mass index (BMI) was also assessed. We compared the conventional treatment planning vs. conformal method. The acute side effects after radiotherapy were also assessed. Patients and Methods: Fifty one women with invasive breast cancer and had indication for SC-LNs irradiation were included. After primary surgery and chemotherapy, patients were divided into 3 groups (n = 17) according to BMI - normal (18.5-24.9), overweight (25-29.9) and obese (≥30). All patients were subjected to three treatment planning techniques, the 1st plan conventionally used 6MV photons prescribed to 1.5 cm, the 2nd plan was also conventional and used 6MV photons prescribed to 3 cm depth, and, the 3rdplan was 3D CT-based conformal combined 6 and 15MV photons optimized manually so as the target volume is covered with 90% of the prescribed dose. The three plans were compared regarding: 1) mean dose to SCF, 2) percent of SCF target covered by >90% of prescribed dose, and, 3) hot spots and mean dose to heart and lung. Then, BMI was correlated with the depth of SCF. Results: Regarding the maximum dose within planning target volume (PTV), 3 rd plan was the best in all BMI classes with lowest hot spots than the other two plans (103.88% in normal, 104.64% in overweight, and 104.23% in obese), followed by 2nd plan (107.7% in normal, 109.88% in overweight, and 107.52% in obese), then 1st plan was the worst plan across in all BMI classes (113.70% in normal, 114.76% in overweight, and 112.64% in obese). The differences were statistically highly significant across the three BMI classes. Regarding the coverage by 90% of prescribed dose, 3rd plan was the best in all BMI classes (96.05% in normal, 95.23% in overweight, and 95.41% in obese) followed by 2nd plan (92.64% in normal, 91.58% in overweight, and76.47% in obese), but1st plan was the worst across all BMI classes (87.76% in normal, 78.52% overweight, and 82.29% in obese). The 3rd plan was the best in all BMI classes having lowest mean heart (nonsignificantly different from the other two plan) and lung dose (high significantly different from the other two plans). Conclusion: The 3D conformal planning for SCLNs had better covering of the target volume and offered more homogenous dose distribution than the two conventional planning across all BMI classes - with lowest heart and lung exposure. 3rd plan of combined 6/15 MV should be a routine treatment planning for SCF in breast cancer.