Dynamic Modulated Brachytherapy for Accelerated Partial Breast Irradiation
M Webster*, D Scanderbeg, C Yashar, D Han, W Song, UCSD Medical Center, La Jolla, CAWE-A-108-7 Wednesday 8:00AM - 9:55AM Room: 108
Purpose: To develop a novel brachytherapy applicator for HDR-based accelerated partial breast irradiation (APBI) that significantly improves upon those commercially available, thereby reducing acute and late side effects seen with current APBI techniques.
Methods: First, the limitations of adjusting the channel placements or placing more channels in a balloon-like multi-catheter ABPI device were explored. Then, a novel tungsten-shielded applicator design was evaluated. The applicator design consists of a 9-mm diameter tungsten rod, density=19.0gm/cm³, with 8 sunken grooves along the edge to allow passage of the ¹⁹²Ir source. Using dose distributions calculated with Monte Carlo (MCNPX), optimized plans were simulated for our devices, as well as the MammoSite and SAVI, for a set of realistic phantom geometries. These geometries, based on patient cases, were ellipsoids of varying sizes with different PTV orientations and a surrounding rind of healthy tissue to be spared.
Results: The benefits of adding more channels become insignificant after about 7 channels. Calculations were done for up to 361 channels, but it was found that this was insufficient to create any noticeable improvement. However, the novel shielded design significantly decreased the V150 and V200, while maintaining the target coverage (V90). All planning variables were superior for this design, except for a modest increase in the total dwell time.
Conclusions: The introduction of additional channels did little to aid the performance of a balloon-like design. There was a very slight benefit to the dose distributions, but not nearly enough to warrant further investigations. Based on these findings, any device based on open isotropic radiation source modulation cannot be improved much further. Therefore, it is necessary to consider designs with directional radiation profiles, which we have shown to give superior coverage. Our new tungsten shielded applicators are a large step forward along the path of brachytherapy applicator development.
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