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 cm(3)). 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.

Postmastectomy electron beam chest wall irradiation in women with breast cancer: a clinical step toward conformal electron therapy.

PURPOSE: Electron beam radiotherapy of the chest wall with or without lymph node irradiation has been used at the Institut Curie for >20 years. The purpose of this report was to show the latest improvements of our technique developed to avoid hot spots and improve the homogeneity. METHODS AND MATERIALS: The study was split into two parts. A new electron irradiation technique was designed and compared with the standard one (dosimetric study). The dose distributions were calculated using our treatment planning software ISIS (Technologie Diffusion). The dose calculation was performed using the same calculation parameters for the new and standard techniques. Next, the early skin toxicity of our new technique was evaluated prospectively in the first 25 patients using Radiation Therapy Oncology Group criteria (clinical study). RESULTS: The maximal dose found on the five slices was 53.4 +/- 1.1 Gy for the new technique and 59.1 +/- 2.3 Gy for the standard technique. The hot spots of the standard technique plans were situated at the overlap between the internal mammary chain and chest wall fields. The use of one unique field that included both chest wall and internal mammary chain volumes solved the problem of junction. To date, 25 patients have been treated with the new technique. Of these patients, 12% developed Grade 0, 48% Grade 1, 32% Grade 2, and 8% Grade 3 toxicity. CONCLUSIONS: This report describes an improvement in the standard postmastectomy electron beam technique of the chest wall. This new technique provides improved target homogeneity and conformality compared with the standard technique. This treatment was well tolerated, with a low rate of early toxicity events.