The validity of Acuros BV and TG-43 for high-dose-rate brachytherapy superficial mold treatments

PURPOSE: The purpose of this work is to validate the Acuros BV dose calculation algorithm for high-dose-rate (HDR) brachytherapy superficial mold treatments in the absence of full scatter conditions and compare this with TG-43 dose calculations. We also investigate the impact of additional back scatter material (bolus) applied above surface molds to the dose distributions under the mold. METHODS AND MATERIALS: The absorbed dose at various depths was compared for simulations performed using either TG-43 or Acuros BV dose calculations. Parameter variations included treatment area, thickness of the bolus, and surface shape (flat or spherical). Film measurements were carried out in a flat phantom. RESULTS: Acuros BV calculations and film measurements agreed within 1.5% but were up to 15% lower than TG-43 dose calculations when no bolus was applied above the treatment catheters. The difference in dose at the prescription depth (1 cm below the central catheter) increased with increasing treatment area: 3.3% difference for a 3 x 3.5 cm(2) source loading area, 7.4% for 8 x 9 cm(2), and 13.4% for 18 x 19 cm(2). The dose overestimation of the TG-43 model decreased when bolus was added above the treatment catheters. CONCLUSIONS: The TG-43 dosimetry formalism cannot model surface mold treatments in the absence of full scatter conditions within 5% for loading areas larger than approximately 5 x 5 cm(2). The TG-43 model results in an overestimation of the delivered dose, which increases with treatment area. This confirms the need for model-based dose calculation algorithms as discussed in TG-186. (C) 2017 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.