UCLA

To achieve more translatable preclinical research results, small animal irradiation needs to more closely simulate human radiation therapy. Although the clinical gold standard is intensity modulated radiation therapy (IMRT), the direct translation of this method for small animals is impractical. To address this challenge, the Sparse Orthogonal Collimator (SOC), a dose-modulating device based on the novel Rectangular Aperture Optimization (RAO) approach, was developed to deliver IMRT on the small animal scale using an image-guided small animal irradiator.

A treatment planning system was developed based on RAO, and several planning experiments were performed for evaluation. RAO achieved highly conformal doses to concave and complex targets, with SOC-based plans achieving superior dosimetry to those optimized for a hypothetical miniature multileaf collimator. Beam commissioning data, including output factors, off-axis factors, and percent depth dose curves, were acquired for our small animal irradiator and incorporated into the treatment planning system. A plan post-processing step was implemented for aperture-size-specific dose recalculation and aperture weighting reoptimization.

The SOC system, with four orthogonal, double-focused tungsten leaf pairs, was designed and fabricated, and control software was developed. The SOC was installed on the small animal irradiator and the alignment was evaluated, with submillimeter shifts measured between the SOC and primary collimator axes over the full gantry rotation. Abutting field and grid dose patterns were created to analyze leaf positioning error, with measured deviations within recommended guidelines. Extremely low leaf transmission was measured, and penumbra was independent of leaf position. Three RAO IMRT plans were delivered and analyzed, with good agreement between the intended and measured dose distributions.

By using advanced optimization techniques, complex IMRT plans were achieved using a simple dose modulation device. The sparse orthogonal collimator was developed and commissioned, with promising preliminary dosimetry results. This platform considerably reduces the gap in treatment plan quality between clinical and preclinical radiotherapy, potentially improving the translation of small animal research results.