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Healthy Tissue Dose Modeling Using Monte Carlo Methods for HDR Ir-192 Breast Brachytherapy Applicators

Y Yang

Y Yang1*, Y Zhang1, M Rivard2, (1) Duke University Medical Center, Durham, NC, (2) Tufts Medical Center, Boston, MA

SU-E-T-335 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The AccuBoost applicators were developed to deliver boost dose to early-stage breast cancer. While efforts have been made to improve dose coverage and skin sparing, dose to healthy tissues such as chestwall and lung has not been quantified. The aim of this study was to simulate dose to these healthy tissues using Monte Carlo (MC) methods for radiation transport.

Methods: The D-Shaped, Round, SDO, and DRO applicators were modified with a bevel tilting 5° away from the breast:chestwall boundary. The MCNP5 code was used for MC simulations. As a preliminary study, the healthy tissues were simulated as 15x15x10cm^3 with breast composition. Dose was normalized to 100% at 3cm depth on CAX of breast. Doses were calculated in breast, on chestwall surface, and into the chestwall using the *F4 FMESH tally with (0.1cm)^3 grid. 10^9 histories gave ~ 3% statistical uncertainties (k=1).

Results: Dose distributions were identical in breast for corresponding flat and beveled applicators. The maximum dose on chestwall surface (mimic the skin) was on source level, with 66%, 66%, 46%, and 49% for flat applicators and 112%, 98%, 93%, and 96% for beveled applicators. Dose at 2 cm depth into chestwall (mimic the rib) was 28%, 24%, 16%, and 18% for flat applicators, while 36%, 27%, 21%, and 21% for beveled applicators. Dose at 5cm depth into chestwall (mimic the lung) was < 10% for both flat and beveled applicators.

Conclusion: As expected, both flat and beveled SDO and DRO applicators provided lower dose to healthy tissue than round applicators due to the internal shielding. Dose to healthy tissues was higher for the beveled applicators than flat applicators, but still not clinically significant compared to the prescription dose.

Funding Support, Disclosures, and Conflict of Interest: Dr. Mark Rivard is a share holder of Advanced Radiation Therapy

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