Dosimetric Comparison between TomoHelical and TomoDirect Radiotherapy in Locally Advanced Left-sided Breast Cancer Patients: A Retrospective Observational Study

Introduction: India has the highest incidence of breast cancer, with treatment typically involving neoadjuvant chemotherapy, surgery, and radiotherapy. Newer techniques like Intensitymodulated Radiation Therapy (IMRT) and tomotherapy, including TomoDirect and TomoHelical, offer improvements over traditional 3Definitive Chemoradiotherapy (DCRT). Aim: To quantify the variabilities of TomoDirect (TD) and TomoHelical (TH) plans for chest wall and Supra-clavicular Fossa (SCF) irradiation in locally advanced left breast cancer treatment. Materials and Methods: The present retrospective observational dosimetric study was conducted from March 2019 to September 2019 at a private cancer centre in eastern India. TD and TH both plans were created in five left breast cancer patients using tomotherapy machine for chest wall and SCF region volumes. The prescription doses for both plans were 50 Gy in 25 fractions. The study measured dosimetric parameters such as Planning Target Volume (PTV) coverage, doses to Organ At Risk (OAR), and treatment times etc. Data analysis was performed using IBM Statistical Package for Social Sciences (SPSS) software, version 25.0. Result: Both plans were almost similar in terms of PTV coverage except for hot areas, which are more common in the TD plans {V107 2.075 cc (TD) vs. 0.4 cc (TH)}. For OARs, values of V5 for the ipsilateral lung and contralateral breast, mean dose (Dmean) were lower in TD, but other parameters were almost similar in both modes. Although TomoHelical improves homogeneity and regulates a high dose gradient better than the TD plan, it comes at the cost of a high integral dose to surrounding normal tissue. The average treatment time is less for TD as compared to TH (mean 325.5 sec vs. 403.35 sec, p-value=0.013). Conclusion: TomoHelical and TomoDirect plans have almost similar PTV coverage and conformity. TD achieves a lower ipsilateral lung low dose area and contralateral breast mean dose, whereas TH offers a more homogeneous plan. Hence, both plans are feasible modes of treatment. For intricate plans, like those incorporating chest wall plus SCF with or without axilla, TH will be a superior option; however, TD will be better for simpler plans, like those that need just chest wall irradiation.