Commissioning of a precision preclinical 200 kV x-ray irradiator based on modular adaptations

Preclinical research in radiation oncology encompasses a range of methodologies, including in vitro cell studies and in vivo small animal experiments, as well as in silico studies to evaluate radiation-induced side effects and tumor responses.

This study addresses the need for high-precision x-ray irradiation solutions as reference for preclinical research. Modifications of an industrial kilovoltage x-ray unit, along with the commissioning of a commercial treatment planning system (TPS), aimed to enable reliable irradiation of small animals in a horizontal beam geometry. All advancements enhancing the irradiation framework are made available, offering cost-effective upgrades for existing systems.

An industrial kilovoltage x-ray unit was equipped with a dual collimation system, featuring a fixed primary and variable secondary collimators with aperture diameters of 5 to 30 mm. Additional modular adaptations were designed and manufactured, including a multimodal mouse bedding unit, a dedicated dosimetry phantom and a quality assurance (QA) phantom. Output factors, percentage depth dose curves and lateral dose profiles were acquired to generate a beam model in the $\mathrm{TPS}\mu$ -RayStation 8B (RaySearch Laboratories, Stockholm, Sweden), using a diamond detector and radiochromic films. Treatment plans for 10 mice were created, evaluated via dose-volume metrics and the homogeneity index and subsequently dosimetrically compared to QA measurements through a gamma analysis with a 1%/ $1mm$ acceptance criterion.

The resulting beam model was validated within a maximum dose deviation of 1.7%. Aperture diameters close to potential target diameters were found to be effective for achieving sufficient target coverage in silico, as demonstrated for a 5 mm target with a homogeneity index of (9.9  $\pm$  0.7)%. Dedicated QA measurements revealed a maximum dose deviation of 1.9% from the TPS and a median gamma passing rate of 100%, confirming the suitability of the proposed solution.

Cost-effective adaptations for an kilovoltage x-ray irradiation framework were designed, manufactured and commissioned, and contribute to the accessibility of preclinical irradiation research. These components are integrated into a comprehensive preclinical particle beam platform.