Optimizing a commercial small animal irradiator for high dose-rate irradiation studies

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Abstract Objective. Preclinical animal studies are essential for discovery of biological mechanisms and translation of novel treatment methods in medical sciences. Small animal irradiator systems are widely used for mechanistic and translational radiation research. These systems commonly operate at a standard geometry with low dose-rates (<5.0 Gy min −1 ). However, some studies require delivering high doses to small animal models, which can take long exposure time using nominal dose-rates of these systems, potentially affecting animal health, increasing uncertainties in delivered dose, and complicating interpretation of outcomes. In this work, we designed, implemented, and characterized a platform for a commercial small animal radiation research platform (SARRP) that enables delivery of x-ray beams at higher dose rates. Approach. A custom-designed mounting assembly and adjustable-height stage were fabricated and used in conjunction with the SARRP. Dosimetric evaluation was performed using radiochromic films at the nominal source-to-surface distance (SSD) of 33 cm and a short SSD of 14 cm corresponding to our apparatus. Film measurements were acquired at the surface and at the depths of 0.5, 1, 1.5, and 2 cm in phantom under open-field conditions as well as with 10 × 10, 5 × 5, 3 × 3 mm 2 square, 1-, and 0.5-mm-diameter circular nozzle settings. Open-field measurements were also performed at SSDs ranging from 35 cm to 8 cm and compared with Monte Carlo simulations. Main results. Dose rate increased by a factor of ∼3–6 times, depending on SSD, measurement depth, and nozzle size. For example, under the 10 × 10 mm 2 nozzle setting, the dose-rate at 10 mm depth in phantom increased from 2.6 Gy min −1 at 33 cm SSD to 14.5 Gy min −1 at 14 cm SSD. This increase primarily followed an inverse square effect between the focal spot and the measurement plane. Significance. Our custom-designed apparatus significantly reduced irradiation time, enabling more efficient, high throughput radiobiology experiments while minimizing anesthesia duration and intra-fraction motion-related effects.

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