SU-E-T-549: Validation of a Commercial Model-Based Collapsed Cone Dose Algorithm for High Dose-Rate Gynecological Brachytherapy Treatment Planning.
PURPOSE
To evaluate the accuracy of calculations from a model-based collapsed cone (MBCC) dose calculation algorithm developed for high dose-rate brachytherapy applications.


METHODS
The algorithm was developed for use in a commercial brachytherapy treatment planning system (Oncentra Brachy, Nucletron an Elekta Company). The MBCC algorithm was used to calculate dose in water for (1) a mHDR-v2 192Ir source, (2) a CT/MR-compatible ovoid applicator set, and (3) a shielded Fletcher-Williamson ovoid. For validation, MBCC algorithm calculations were compared to Monte Carlo (MC) simulations for equivalent geometries. The MC models were constructed using a multi-purpose code, and were previously benchmarked against film measurements. The resulting dose distributions from each calculation approach were compared using isodose overlays and gamma analysis using 2% dose difference and 2 mm distance to agreement metrics.


RESULTS
Comparison of the MBCC and MC calculations for the 192Ir source and the CT/MR compatible ovoid set demonstrated excellent agreement, with 100% of MBCC dose points showing agreement within the stated criteria. As expected, agreement between MBCC and MC was lower for the shielded Fletcher-Williamson tandem and ovoid applicator set due to the presence of high-density tungsten alloy shields. However, even in this case, the MBCC algorithm showed 95.5% and 97.4% of dose points within the stated tolerance of the MC calculation in the mid-plane and cross-plane of the ovoid, respectively. All MBCC dose points showed 100% agreement with MC calculations beyond 5 mm the ovoid shields.


CONCLUSION
The MBCC dose algorithm demonstrates excellent agreement with MC calculations for various gynecological brachytherapy applicator components in water, and offers the potential to improve the accuracy of dose calculations compared with current, clinically-utilized TG-43 calculations. research was funded by a grant from Nucletron, an Elekta Company.