Dosimetric commissioning of small animal FLASH radiation research platform

<i>Objective.</i>The FLASH-SARRP, a new small animal radiation research platform has been designed to support conventional, high and ultrahigh dose-rate kV x-rays for preclinical research. This self-shielded system features two high-capacity x-ray sources with rotating-anode technology. This study characterizes the dosimetric and mechanical performances of the system for preclinical FLASH radiation research.<i>Approach.</i>Mechanical alignment of two x-ray tubes was performed using a custom-designed jig by aligning the outlet ports of the tube housings. Alignment of mechanical and radiation centers was evaluated by scanning a highly-collimated slit across the focal-spot. The linearity of the x-ray tube voltage, current and exposure-time was evaluated using silicon diode and ion-chamber detectors. Dosimetric characteristics of beam e.g. output linearity, depth dose-rate and profiles were measured using calibrated radiochromic films, thermoluminescence, and ion-chamber detectors in kV solid-water phantom or air, with and without external energy filtration. Dose-rate uniformity, flatness, symmetry, beam width, and penumbra were assessed for single and parallel-opposed x-ray beams across various field sizes.<i>Results.</i>The x-ray sources were aligned at 0.3 mm accuracy. The radiation beam center was within 1.0 mm of mechanical center. Beam output was highly linear with wide ranges of tube current (5-630 mA) and exposure-time (5-6300 ms), supporting accurate dose-rate and dose adjustments. The FLASH-SARRP supports a wide range of dose-rates from <1 Gy s^-1to 100 Gy s^-1, depending on field size. The uniformity of the depth and crossbeam dose-rates is ±3.6 Gy s^-1and ±1.5 Gy s^-1between 5-15 mm phantom depth without and with external filter, respectively.<i>Significance.</i>The FLASH-SARRP provides desirable dosimetric performance for small animal irradiation, supporting both conventional and FLASH dose-rate across field sizes from 5 mm-diameter circular to 20 mm-square apertures. This platform enables comparative studies between FLASH and conventional dose-rates in small animal (e.g. mouse) models.