Dosimetric Comparison of Tangential Beam and Equally Spaced Beam Intensity-modulated Radiation Therapy in Right Breast Cancer Following Breast-conserving Surgery: A Retrospective Study

Objective: This study aimed to evaluate and compare the dosimetric performance and treatment efficiency of two intensity-modulated radiation therapy (IMRT) techniques – tangential field IMRT (Tan_IMRT) and equally spaced beam IMRT (Esb_IMRT) – in patients with right-sided breast cancer following breast-conserving surgery (BCS). Materials and Methods: A total of 25 female patients who underwent BCS for right-sided breast cancer and received adjuvant radiotherapy were included in this retrospective study. All patients were treated with whole-breast hypofractionated radiotherapy, delivering 40.05 Gy in 15 fractions. Each patient’s treatment plans were generated using the Eclipse Treatment Planning System, employing Tan_IMRT and Esb_IMRT techniques on a TrueBeam SVC linear accelerator equipped with a high-definition multileaf collimator. Various dosimetric parameters were evaluated, including the conformity index (CI), homogeneity index (HI), dose–volume histogram metrics for organs at risk, and monitor units (MUs). Results: In right-sided breast radiotherapy following BCS, Esb_IMRT demonstrated a superior CI and HI compared to Tan_IMRT. In addition, Esb_IMRT achieved lower ipsilateral lung doses, as reflected by reduced V20%, V5%, and mean dose (D mean ). However, Tan_IMRT resulted in a lower D mean for the contralateral breast. Conclusion: Tan_IMRT shows reduced radiation exposure to the heart, contralateral lung, and contralateral breast. Furthermore, Tan_IMRT delivers doses with fewer MUs. In contrast, Esb_IMRT gives superior CI and HI while achieving lower doses to the ipsilateral lung and liver. Hence, Tan_IMRT can be suitable for younger patients.