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High Energy Brachytherapy Dosimetry as It Applies to Accelerated Partial Breast Irradiation (APBI)

S Richardson

F Mourtada

S Richardson1*, F Mourtada2*, (1) Swedish Medical Center-Tumor Institute, Seattle, WA, (2) Christiana Care Hospital, Newark, DE

TU-A-137-1 Tuesday 8:00AM - 8:55AM Room: 137

Report 229 is the newest report on high energy brachytherapy dosimetry. It investigates many known issues with accurately doing brachytherapy dose calculations and modeling of TG43 parameters for sources with photon energies >50keV. Two issues that are described in the report are the presence of tissue heterogeneities and scatter corrections when doing brachytherapy treatments. Both of these issues are well manifested when doing partial breast brachytherapy. The applicators for breast brachytherapy are either filled with high Z contrast material (Mammosite or Contura) or are filled with air (Savi) which can create either a dose decrease or dose increase in the PTV compared to a standard TG43 calculation. Often times when these devices are used, the applicators are in close proximity to the skin surface which results in a loss of CPE and can actually decrease the dose compared to what one would expect when doing a TG43 calculation. The applicators are also sometimes near the lung or ribs which also creates a dose discrepancy compared to treatment planning systems. The purpose of this talk will be to describe the physics behind these issues and provide an overview of published literature which investigates the nature of the dose discrepancies encountered with partial breast brachytherapy. It will also describe the magnitude of the dose discrepancy for a variety of clinical cases.

Learning objectives:
1.To understand the physics behind high energy brachytherapy as applied to APBI
2.To understand when TG43 calculations may not accurately describe the clinical situation
3.To understand the nature of these dose discrepancies and be able to provide magnitudes for clinical approximations

Funding Support, Disclosures, and Conflict of Interest: Some of the research presented was funded by an MRA with Varian Medical Systems.

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