Room: Davidson Ballroom A
Purpose: Small animal studies are essential for evaluating the safety and efficacy of new radiotherapy strategies, but their translatability to clinical outcomes is limited by crude irradiation techniques. Although image guided small animal irradiators have been recently developed, they lack the necessary hardware for intensity modulated radiotherapy (IMRT). Since it is infeasible to scale down the multileaf collimator (MLC) for small animals, we are developing a new dose modulation device, the sparse orthogonal collimator (SOC), to deliver micro-IMRT with novel rectangular aperture optimization (RAO).
Methods: The SOC has two orthogonal sets of double-focused tungsten leaf pairs with tongue-and-groove geometry. An Arduino board controls the stepper motors driving each leaf (4 cm/sec, 0.02 mm resolution). The SOC attaches to the X-ray tube of the PXi X-RAD system, maintaining full clearance to maximize coplanar beam space. A planning system was created for the mouse scale based on convolution dose calculation and RAO fluence map optimization, performed with an arbitrary rectangular basis and a regularization term on the number of apertures per beam. RAO plans for total liver irradiation were created using contrast-enhanced mouse CT.
Results: A SOC prototype was developed, with machined tungsten leaves and 3D-printed carbon fiber housing, as well as system control software with a graphical user interface. The prototype was installed on the X-RAD with preliminary alignment and dosimetry tests performed. A 4x4 checkerboard pattern of 5 mm squares was delivered to film, with 96% of pixels matching the intended distribution. The mouse RAO plan achieved a conformal dose to the liver while sparing organs-at-risk.
Conclusion: The SOC has been developed to enable IMRT for pre-clinical small animal studies, potentially yielding much more clinically relevant results. Using RAO for fluence map optimization, the SOC bridges a critical gap in achieving highly modulated dose distributions without complex MLC hardware.
Funding Support, Disclosures, and Conflict of Interest: NIH U19AI067769 DE-SC0017687 NIH R21CA228160 DE-SC0017057 NIH R44CA183390 NIH R43CA183390 NIH R01CA188300