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Validating a 192Ir-Based Small Animal Irradiation Apparatus Using a 3D-Printed Applicator: Comparison Between TG-43, Monte Carlo and Films Dosimetry

K Nie

K Nie1*, C Collins Fekete2, D Pinnaduwage1, J A M Cunha1, K Mellis1, M Descovich1, L Beaulieu2, J Pouliot1, (1) Department of Radiation Oncology, University of California San Francisco, San Francisco, CA, USA ((2) Universite Laval, Centre Hospitalier Univ de Quebec, Quebec, QC, Canada

WE-E-108-10 Wednesday 2:00PM - 3:50PM Room: 108

Purpose: Accurate assessment of dose delivered is key to early prediction of radiation-induced anatomic and physiologic changes vital in providing the most accurate patient-specific treatments. We are conducting a translational small-animal study using functional Hyperpolarized-13C-Urea with DCE-MRI to evaluate tumor perfusion changes following local targeted Ir-192 irradiation using the Leipzig applicator. The purpose of this study is to present and evaluate a novel Monte Carlo (MC) tool, which provides heterogeneous dose predictions for this specific application, and to compare the results against the TG-43 dose calculation.

Methods: CT scans were obtained with a Leipzig applicator mold (fabricated using a 3D-printer to avoid metal artifact) centrally placed on top of the CyberKnife Ball Cube QA phantom . The CT density of the mold was overridden to be that of the applicator material, Tungsten. A Monte Carlo platform, ALGEBRA (ALgorithm for heterogeneous dosimetry based on GEANT4 for BRAchytherapy) was used for simulation. Dose measurements were done using Gafchromic EBT2 film placed orthogonally inside the Ball Cube exposed to Ir-192 with the Leipzig applicator in place. Simple TG-43 calculations for a free source in water was done using the Oncentra treatment planning system.

Results: The two-dimensional planar dose distributions obtained from MC simulation showed strong agreement (within 4-5%) with dose measurements while TG-43 calculations showed differences up to 20%. Compared to TG-43, the MC result was attenuated less at the surface because of the Leipzig air cavity, but penetrated less due to the collimation effect.

Conclusion: We have validated a new MC simulation tool using a Leipzig applicator for small animal irradiation. This tool will provide the basis for studies associating tumor response with the actual dose delivered. The tool can be further used to construct dosimetry information for clinical treatments using the Leipzig applicator as an alternative to superficial/orthovoltage radiation treatment.

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