Aim/goal: Forward planned intensity-modulated radiation therapy (forward IMRT) with apnea technique (BH) is considered optimal by most practitioners for the treatment of left breast cancer. Regional nodal irradiation, including armpit and supraclavicular fossa (SCF) augmentations, may increase dose to organs at risk (OAR), particularly the lungs. This study was performed to evaluate the potential of reverse planned IMRT (inverse IMRT) to achieve significant dose reduction at OAR.
Materials and methods: Ten patients with left breast cancer treated with the Active Breath Co-ordinator BH technique were included in the study. Forward IMRT planes were generated in both BH and free-breathing (FB) scans. Inverse IMRT planes were generated in FB scan using the Tomotherapy-Direct and Tomotherapy-Helical techniques. Contouring was performed in accordance with ESTRO Consensus Contouring Guidelines. The prescribed dose was 40 Gy in 15 fractions. Statistical significance was tested using one-way ANOVA for parametric data and Kruskall-Wallis test for non-parametric data. Multiple comparison tests were performed using the Bonferroni test. P
Results: Reverse IMRT plans achieved a higher homogeneity index compared to direct IMRT with BH. Tomotherapy-Reduced dose direct to ipsilateral lung, compared to prior IMRT with BH while achieving similar doses to other OARs. Tomotherapy-helical planes had a significantly better compliance index and reduced maximum dose to the left anterior descending artery compared to forward IMRT planes, but low dose to other OARs was significantly worse.
Conclusion: For radiation therapy to the left breast, armpit and SCF, reverse IMRT with the Tomotherapy-Direct plane achieved a better homogeneity index and reduced dose to the ipsilateral lung compared to forward IMRT with BH .
Key words: Breast cancer; IMRT; radiotherapy; tomotherapy.