TU-C-BRB-01: Commissioning and Characterization of a Dual Gantry Image Guided Orthovoltage Micro Irradiator for Preclinical Small Animal Radiobiological Experiments

Abstract

Purpose: The purpose of this study was to accurately commission and characterize our small animalimage guided micro irradiator, the microIGRT, for preclinical translational radiobiological research. The microIGRT has a dual gantry architecture with a microCT subsystem gantry for low dose high resolution anatomical imaging and treatment planning, and a second coaxial microRT subsystem gantry for conformal image guided orthovoltage irradiation. Methods: The microCT image resolution, contrast, and dose were evaluated with specialized phantoms and animal models. The micro RT subsystem percent depth dose, beam profile, multibeam irradiation precision and conformality, animal repositioning accuracy, mechanical resolution, and dosimetric accuracy were measured using specialized phantoms equipped with radiochromic film. For each measurement, results were compared with standards adapted from external beam Linac and patient quality assurance protocols scaled to animal dimensions and orthovoltage energies. Results: The microCT dose is 4.15 cGy/scan for 100 um imaging resolution, up to 33.2 cGy/scan for 800 um imaging resolution. The percent depth dose for a 300 kVp beam with 3.8 mm of Cu HVL is 2.7 cGy/mm with a buildup of 2.8 mm. A 1 cm2 standard square field has a 265 um penumbra, 7% homogeneity, and 9% symmetry. Anatomical positioning is within 500 um for fractionated treatments and multibeam isocentric irradiation central axis uncertainty is within a 150 um radius for three, four, and five coplanar beam treatments. Conclusions: We characterized the small animal microIGRT developed by our group to provide complete parameterization of the instrument's imaging and treatment capabilities. Anatomical imaging, irradiation distributions, and beam dosimetry indicate that our system satisfies requirements established by scaling clinical imaging and radiotherapy protocols to animal models to perform clinically relevant translational radiobiological experiments.