Synchronous bilateral breast cancer irradiation: clinical and dosimetrical issues using volumetric modulated arc therapy and simultaneous integrated boost

The aim of the present retrospective analysis was to evaluate dosimetric parameters, feasibility and outcome for Synchronous Bilateral Breast Cancer (SBBC) patients treated with adjuvant radiotherapy (RT) by Volumetric Modulated Arc Therapy (VMAT). From September 2011 to April 2016, 1100 Breast Cancer (BC) patients were referred to our institution to receive adjuvant breast RT, and those with SBBC were selected for the present analysis. A total of 16 patients were identified. A total dose of 50 Gy in 25 fractions was prescribed to the Planning Target Volume of the whole bilateral breast (PTVBN) with or without the supraclavicular and infraclavicular nodes, while a total dose of 60 Gy in 25 fractions was prescribed to the surgical bed (PTVboost). Several V (xGy) and Dx% parameters were analyzed for the PTVs, together with Conformity and Homogeneity indexes (CI, HI), and for the critical Organs at risk (OARs), lungs and heart first. With a median follow-up of 24 months, no acute or late side effects more than grade 2 were observed. All patients are alive without any sign of disease. For target dose coverage, our observed inter-patients averages (+/- 1 sd) were V (95% Dp) = 96.7 +/- 1.6% (96.3 +/- 1.8%) to the left (right) PTVBN, V (95% Dp) = 98.6 +/- 2.7% (99.4 +/- 0.9%) to the left (right) PTVboost, and D (2%) = 64.4 +/- 1.8 Gy (65.0 +/- 2.0 Gy) to the left (right) PTVboost, respectively. With regard to the heart, the inter-patient average of D (mean) was 8.3 +/- 3.3 Gy. For the lungs, the inter-patient average of D (mean), V (5 Gy) and V (20 Gy) were 11.8 +/- 2.3 Gy, 78.9 +/- 15.3% and 15.7 +/- 5%, respectively. The present retrospective analysis showed the feasibility, tolerability and safety of VMAT in the treatment of SBBC patients. Further studies are necessary to confirm these preliminary data.