Comparative Dosimetric Evaluation of Intensity-Modulated Radiation Therapy (IMRT) Using a Linear Accelerator and Helical Radixact Tomotherapy for Highly Complex Breast Cancer Targets
Abstract
Purpose
To perform a dosimetric comparison of Intensity-Modulated Radiation Therapy (IMRT) plans generated using Varian C-arm linear accelerator (LINAC) and Radixact Helical TomoTherapy (TOMO) for breast cancer patients with highly complex, large target volumes, requiring regional lymph node irradiation.
Methods
Treatment plans were retrospectively generated for six patients (four left-sided and two right-sided) using Eclipse for LINACs and Precision for TOMO. All plans were prescribed 5000 cGy delivered in 25 fractions. Plan evaluation included target coverage (D95%), doses to ipsilateral lung, heart, left anterior descending artery (LAD), and contralateral lung and breast. Dose-volume metrics were selected based on clinical relevance and institutional planning constraints. Plans were also quantitatively assessed using Conformity Index (CI), Conformation Number (CN), Gradient Index (GI), and Homogeneity Index (HI).
Results
Both modalities achieved clinically acceptable target coverage for all patients, with PTV D95% >= 95%. TOMO demonstrated superior plan quality, with higher conformity (CI/CN) and improved dose homogeneity (mean HI: TOMO 0.122, IMRT 0.164). In left-sided cases, TOMO consistently yielded lower mean heart (3.12-4.50 Gy) and mean LAD doses (3.22-5.11 Gy) compared to IMRT (heart: 3.74-6.85 Gy; LAD: 5.83-7.20 Gy), although high-dose heart metrics showed variable trends across patients. TOMO also reduced contralateral lung (D5%) and contralateral breast (Dmean, D3%) doses in left-sided cancer. Ipsilateral lung (D20%) showed mixed behavior, with TOMO frequently associated with slightly higher values. In right-sided, IMRT resulted in lower cardiac and contralateral organ doses, indicating improved limitation of low-dose spread to contralateral structures.
Conclusion
TOMO offers advantages in target conformity, dose homogeneity and reduced mean heart and LAD dose in left-sided breast cancer, while IMRT may better limit contralateral organ exposure in right-sided cases. Dosimetric trade-offs are strongly influenced by tumor laterality and anatomical context, underscoring the importance of case-specific interpretation when selecting treatment techniques for complex breast radiotherapy.