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Dose Rate Determination for Preclinical Total Body Irradiation

Y Zhong1*, Y Lai2, S Stojadinovic1, M Story1, X Jia1, (1) UT Southwestern Medical Center, Dallas, TX, (2) University of Texas at Arlington, Arlington, Texas

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
The accuracy of delivered radiation dose and the reproducibility of employed radiotherapy methods are key factors for preclinical radiobiological research. In this study Monte Carlo simulations and measurements were used to accurately determine the dose rate for total body irradiation (TBI) setup--a classic radiobiology experiment.

Methods:
Several phantom configurations, including large solid water slab, small 3D printed water tank and customized rodentomorphic mouse and rat phantoms made of silicon rubber were simulated and measured for TBI setup utilizing a preclinical irradiator XRAD320 (PXI, North Branford, CT). The irradiator calibration and the phantom measurements were performed using ADCL calibrated ionization chamber (PTW Freiburg, Germany) following the AAPM TG61 protocol. The Monte Carlo simulations were carried out using GATE to simulate absorbed dose distributions for all phantom configurations.

Results:
All simulated and measured dose rates had favorable agreement with relative dose differences within 3%. However, the study indicated large dose deviations if calibration conditions are assumed for a given experimental setup as commonly done for quick determination of irradiation times utilizing lookup tables and hand calculations. In a TBI setting, the reference calibration geometry at an extended source-to-surface distance and a large reference field size is likely to overestimate true phantom scatter. Consequently, measured/simulated and hand calculated TBI dose rates in this study had large dose variances: 15% for a large solid water slab, 25% for a small water box, along with 30% and 36% for mouse and rat phantoms, respectively.

Conclusion:
Small changes in experimental setup could result in large calculated and measured dose discrepancies from the reference value. Monte Carlo simulations and the corresponding measurements specific to a designed experimental setup is vital for accurate preclinical dosimetry and reproducibility of radiobiological findings. This study supports well recognized idea that physics consultation is highly recommended for all radiobiology investigations.

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