Concepts for critical organ dosimetry in three-dimensional image-based breast brachytherapy

PURPOSE: To investigate dose-volume histogram (DVH) parameters for organs at risk (OARs) in sectional three-dimensional image-based accelerated partial breast irradiation. METHODS AND MATERIALS: Skin, lung, and ribs were defined as OARs and the heart was discussed. Two different skin-contouring methods were tested on phantom before applying to the patient cohort. First, an inside skin wall contour was delineated with three different wall thicknesses to demonstrate the influence of contouring on DVH parameter. Second a structure was defined, delineated outside of the phantom surface, such that a three-dimensional skin volume was extended like a virtual bolus contour. Point dose values and DVH parameters were reported for 25 patient cases. RESULTS: The DVH parameters D-0.1 (cc) = 65 +/- 21, D-1 cc = 45 +/- 8, D-10 cc = 30 +/- 4 cGy/pulse for the outside skin structure around the breast corresponded to skin surface areas of 1 +/- 1, 6 +/- 3, and 6 +/- 11 cm(2). Lung volume receiving 20 Gy(alpha beta 3) was 8.3 +/- 11 cm(3). D-0.1 cc and D-2 cc in the most exposed rib were 0.7 +/- 0.3 and 0.4 +/- 0.2 Gy/pulse, respectively. CONCLUSION: In accelerated partial breast irradiation treatment planning, dose to OAR can be reported in a more sophisticated way with DVH parameters than using points only. The suggested method of skin delineation using the defined outside structure allows calculating reliable and reproducible DVH parameters. (C) 2008 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.