A custom three-dimensional electron bolus technique for optimization of postmastectomy irradiation

Purpose: Postmastectomy irradiation (PMI) is a technically complex treatmen t requiring consideration of the primary tumor location, possible risk of i nternal mammary node involvement, varying chest wall thicknesses secondary to surgical defects or body habitus, and risk of damaging normal underlying structures. In this report, we describe the application of a customized th ree-dimensional (3D) electron bolus technique for delivering PMI. Methods and Materials: A customized electron bolus was designed using a 3D planning system. Computed tomography (CT) images of each patient were obtai ned in treatment position and the volume to be treated was identified. The distal surface of the wax bolus matched the skin surface, and the proximal surface was designed to conform to the 90% isodose surface to the distal su rface of the planning target volume (PTV). Dose was calculated with a penci l-beam algorithm correcting for patient heterogeneity. The bolus was then f abricated from modeling wax using a computer-controlled milling device. To aid in quality assurance, CT images with the bolus in place were generated and the dose distribution was computed using these images. Results: This technique optimized the dose distribution while minimizing ir radiation of normal tissues. The use of a single anterior field eliminated field junction sites. Two patients who benefited from this option are descr ibed: one with altered chest wall geometry (congenital pectus excavatum), a nd one with recurrent disease in the medial chest wall and internal mammary chain (IMC) area. Conclusion: The use of custom 3D electron bolus for PMI is an effective met hod for optimizing dose delivery. The radiation dose distribution is highly conformal, dose heterogeneity is reduced compared to standard techniques i n certain suboptimal settings, and excellent immediate outcome is obtained. (C) 2001 Elsevier Science Inc.