The influence of patient geometry on the selection of chest wall irradiation techniques in post-mastectomy breast cancer patients

Background and purpose: To evaluate three chest wall (CW) irradiation techn iques: wide tangential photon beams, direct appositional electron field and electron are therapy with regards to target coverage and normal tissue tol erance. Materials and methods: Thirty-two post-mastectomy breast cancer patients we re planned using three CW irradiation techniques. Computed tomography (CT) simulation was done on all patients and clinical target, heart and lung vol umes were contoured. For each technique, dose distributions and dose-volume histograms (DVH) were calculated. Pass/fail criteria were applied based on volumetric target and critical structure dose coverage. Passing criteria f or target was 95% of target receiving 95% of dose using a standard dose of 50 Gy/25 fractions, for heart less than or equal to 10% volume receiving 50 % dose (i.e. 25 Gy) and for lung less than or equal to 25% volume ipsilater al lung receiving 50% dose (i.e. 25 Gy). Results: The number of patients optimally treated by each technique were as follows: wide tangential photon beams 23/32 (72%), direct appositional ele ctron field 1/32 (3%), electron are 4/32 (12.5%) and in 4/32 (12.5%) no tec hnique was optima. Geometric predictors for technique suitability include C W thickness, medial to lateral CW curvature, uniformity of superior to infe rior CW curvature and length of mastectomy scar. Conclusions: This study confirms the utility of CT planning and DVH analysi s for treatment planning of breast cancer. Patient factors that predict for treatment technique suitability and aid in technique selection can be iden tified. In a small subset of patients, none of the currently studied techni ques were optimal and more novel methods of chest wall irradiation are requ ired. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.