Whole breast radiotherapy in the lateral decubitus position: A dosimetric and clinical solution to decrease the doses to the organs at risk (OAR)

Purpose: To evaluate whole breast 3D-conformal radiotherapy (RT) delivered in the lateral decubitus position (isocentric lateral decubitus [ILD]) and to report the acute toxicity of a series of consecutive patients treated with ILD. Materials and methods: From January to December 2010, 56 consecutive patients with large breasts and early-stage breast cancer treated by breast conserving surgery underwent 3D-conformal whole breast RT in the lateral decubitus position. A dose of 50 Gy in 25 fractions via two opposed isocentric beams was prescribed to whole breast, with or without a 16 Gy photon tumor bed boost. Dosimetry of all patients was reviewed, and the acute toxicity of treatment, evaluated weekly using the NCI CTC v3.0 scale, was analyzed. Results: Median age was 57 years (range: 33-71). 85% of patients had a breast circumference of at least 95 cm and 80% had at least a C cup size. Average breast volume was 991 cm(3) (range: 225-2791 cm3). Median dose to the breast was 50 Gy, while median dose to the tumor bed was 16 Gy. Grade 1, 2 and 3 dermatitis developed in 37.5%, 58.9% and 1.8% of patients, respectively. From a dosimetric point of view, doses to the ipsilateral lung were extremely low: average V-1Gy, V-2Gy and V-5Gy were 26.6%, 9.3% and 0.7%, respectively. Average mean lung dose was 0.96 Gy. For the 26 patients with left-sided tumors, heart doses were also extremely low: average V-1Gy, V-2Gy and V-5Gy were 58.8%, 14.2% and 0.7%, respectively. Average mean heart dose was 1.35 Gy. Conclusion: Whole breast radiotherapy in the lateral decubitus position for patients with large breasts and early-stage breast cancer provides an excellent dosimetric profile, with low doses to the heart and ipsilateral lung. It is also very well tolerated, with a good acute toxicity profile. (C) 2013 Elsevier Ireland Ltd. All rights reserved.