First clinical report of helical tomotherapy with simultaneous integrated boost for synchronous bilateral breast cancer.

Objective: Radiotherapy (RT) for synchronous bilateral breast cancer (SBBC) is technically very challenging. This study reports the clinical feasibility, dosimetry and safety of helical tomotherapy (HT) with simultaneous integrated boost (SIB) in patients treated with adjuvant radiotherapy for SBBC.

Methods: 21 women with SBBC treated with HT from January 2013 to June 2016 were retrospectively evaluated. Radiation lung toxicity was assessed using pulmonary function test (PFT) and high-resolution computerized tomography scan (HRCT) scan at baseline and 1 yearpost-RT in 18 patients. Survival was calculated using Kaplan-Meier curves. Significance of the difference between pre- and post-RT PFT values was assessed using paired t-test.

Results: The dose prescription was 50Gy to the breast, chest wall or regional nodes and 61Gy to the tumour bed as SIB, delivered in 25 fractions. Dosimetric outcome was excellent both for target volumes and normal tissues. Acute skin and oesophageal toxicities were minimal. Symptomatic radiation-induced pnuemonitis was not observed. Subclinical radiological Grade I-II changes were apparent in 14 patients. Only one patient developed Grade III radiological change whereas no change was documented for three patients. PFTs did not show any significant change in any of the measured parameters. At a median follow-up of 25 months, 3-year disease-free survival, overall survival and loco-regional control were 65.6%, 83.3% and 85.7% respectively.

Conclusion: Women with SBBC can be safely treated with HT and this is not associated with adverse short- to intermediate term radiation toxicity. Advances in knowledge: This is the first report that establishes the safety of HT for adjuvant RT using SIB technique in SBBC.