Modeling of the direction modulated brachytherapy tandem applicator using the Oncentra Brachy advanced collapsed cone engine

PURPOSE: The direction modulated brachytherapy (DMBT) magnetic resonance-compatible tandem applicator, made from a tungsten alloy rod, has six symmetric peripheral grooves, designed specifically to enhance intensity modulation capacity through achieving directional radiation dose profiles. In this work, the directional dose distributions of the DMBT tandem were modeled and calculated with the Oncentra Brachy advanced collapsed cone engine (ACE), which was validated against Monte Carlo (MC) calculations. METHODS AND MATERIAL: The prototype 3D tandem applicator model was created for use in the Oncentra Brachy treatment planning system. The Ir-192 source was placed inside a DMBT tandem in one and six channels as a single dwell position (DP) per channel with the same index length, as well as 1 DP in a standard tandem. Dose distributions were calculated in a water medium by both ACE and MC and compared. RESULTS: For 1DP/6DP inside the DMBT and 1DP inside the standard tandem, respectively, the mean dose differences were 3.5/3.3% and <2.8% with the range of 0.1%-6.5%/0.2%-5% and 0.1%-5%, between ACE and MC, respectively. CONCLUSIONS: The DMBT tandem is successfully modeled in a commercial treatment planning system. The ACE algorithm is capable of accurately calculating highly directional dose distributions generated by a dense tungsten alloy contained within the DMBT tandem, with agreements achieved within <3.5%. (C) 2018 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.