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Characterization of a Novel EPID Dosimetry System for KV X-Ray Exit Dose Verification in Pre-Clinical Studies

A Anvari*, Y Poirier , A Sawant , University of Maryland School of Medicine, Baltimore, MD


(Wednesday, 8/1/2018) 10:00 AM - 10:30 AM

Room: Exhibit Hall | Forum 3

Purpose: Small animal image-guided radiotherapy (SA-IGRT) systems closely emulate the clinical radiotherapy environment and process. The dose delivery accuracy of these systems depends on a number of operator- and system-related factors which can individually or cumulatively contribute to significant dosimetric errors. Since tumor response and normal tissue toxicity are radiation dose-dependent, accurate treatment dose verification is important in pre-clinical studies. Here, we develop an EPID transmission and in-phantom exit dosimetry method for kilovoltage (kV) x-ray beam dose verification in SA-IGRT systems.

Methods: We calibrated the in-built EPID on the small animal radiation research platform (SARRP, XSTRAHL, Inc.) to measure transmission dose at the detector plane. Accuracy of two-dimensional (2D) transmission dose distributions against ion chamber (IC) and film measurements was validated for a range of x-ray tube currents, object thicknesses, and collimator sizes. To calculate the dose delivered to an object, the EPID transmission dose was back-projected to the beam’s exit surface. Accuracy of the dose distribution was then compared against IC and film measurements for several collimators at varying thicknesses of homogeneous and inhomogeneous phantoms.

Results: Transmission dose values measured with the EPID showed close agreement with film and IC measurements, for tube currents higher than 10 mA (≤0.4%), various phantom thicknesses (≤2.4%), and multiple cone sizes (≤2.9%). For phantom thicknesses ≥15 mm, calculated exit doses agreed with IC and film values within ≤2.5% and ≤3.2%, respectively. As small animals typically have ≥15 mm thickness, these results imply that the EPID is capable of accurate exit dose calculation in preclinical studies. For inhomogeneous phantom, the EPID and film exit dose measurements agreed within ≤2.7%.

Conclusion: We developed and validated a novel 2D transit/exit dosimetry in kV x-ray energies using an EPID. This system shows promising potential for performing in-vivo kV x-ray dose verification in pre-clinical studies.


Electronic Portal Imaging, Dosimetry


TH- Small Animal RT: Development (new technology and techniques)

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