Simultaneous Bilateral Chest Wall Irradiation, Can Helical Tomotherapy Improve Dose Distribution?

Background: Radiotherapy to bilateral breast cancer (BBC) is technically challenging because of the proximity to organs as the heart and lungs. Aim: We conducted this study tocompare helical tomotherapy (HT) to 3-dimensional conformal radiation therapy (3D-CRT) technique in bilateral chest wall irradiation regarding the coverage of target volume and the doses recorded at adjacent organs at risk. Methods: Ten patients with synchronous BBC who underwent bilateral mastectomy were included. Two plans were performed for each patient using HT and 3D-CRT. Results: Target volume included bilateral chest wall, bilateral supraclavicular and level III axillary lymph nodes. Prescription dose was 50 Gy/25 fractions in 5 weeks. The mean chest wall planning target volume (PTV) homogeneity index and conformality index were 0.15 and 1.09 in HT versus 0.37 and 1.43 in 3D-CRT plans (p= 0.012 and 0.031). At least 95% of the prescribed dose was covering 96% and 92% of the chest wall PTV for HT and 3D-CRT plans (p= 0.026). Helical tomotherapy plans achieved significant decrease in all cardiac parameters compared to 3D-CRT plans. Helical tomotherapy also achieved reduction in mean dose and V20 for both lungs in expense of higher low dose to normal healthy tissue and longer treatment time in comparison to 3D-CRT. Conclusion: For BBC patients treated with bilateral chest wall and supraclavicular lymph nodes irradiation, HT provides more conformal and homogenous plan than conventional 3D-CRT plans. Helical tomotherapy improves chest wall PTV coverage and decreases the dose to the heart and lungs in expense of more volume of normal tissues exposure to low doses of radiation and longer treatment time.