Aim To compare quality of life and radiation toxicity in patients applied with Tomo-helical intensity-modulated radiation therapy (IMRT) and three-dimensional conformal radiation therapy (3D-CRT) as adjuvant radiotherapy because of breast cancer. Material and method The study included a total of 403 patients. Fifty-eight percent of patients were treated with 3D-CRT, and 42% of patients were treated with Tomo-helical IMRT. Radiation toxicity was evaluated according to the Radiation Therapy Oncology Group (RTOG) toxicity criteria. Quality of life was evaluated using the European Organisation for Research and Treatment of Cancer (EORTC) QLQ-C30 Quality of life scale version 3-Turkish and the EORTC QLQ-BR23 questionnaires. These questionnaires were completed by all patients at 4 different time points: the start of RT (T-1); the end of RT (T-2); 1 month after completion of RT (T-3); and 6 months after completion of RT (T-4). Statistical data were analysed using the Chi-square and MANOVA tests. Results Radiotherapy-related skin, upper gastro-intestinal system, white blood count and neutrophil toxicity were observed to be higher in the patients treated with 3D-CRT (p < 0.001). No difference was determined between the radiotherapy techniques according to the EORTC-C30 (p > 0.050). In the patients treated with Tomo-helical IMRT, the scores of breast symptoms (p = 0.014), sexual function (p = 0.003) and sexual pleasure (p = 0.020) in the sub-dimension scales of the EORTC-BR23 were found to be better compared with those of patients treated with 3D-CRT. Conclusion The findings of RT toxicity and quality of life appear to be superior in patients applied with Tomo-helical IMRT compared with patients treated with 3D-CRT.