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Commissioning and Testing of the Sparse Orthogonal Collimator for Small Animal IMRT

K Woods1*, R Neph1 , D Nguyen2 , D O'Connor3 , K Sheng1 , (1) UCLA School of Medicine, Los Angeles, CA, (2) UT Southwestern Medical Center, Dallas, TX, (3) University of San Francisco, San Francisco, CA


(Wednesday, 7/17/2019) 4:30 PM - 6:00 PM

Room: 304ABC

Purpose: Preclinical studies are critical for the advancement of radiation therapy research, but there can be a lack of clinical translatability due to the disparity in treatment delivery techniques between small animal subjects and human patients. To bridge this gap, we are developing the Sparse Orthogonal Collimator (SOC), a dose-modulating device based on the novel Rectangular Aperture Optimization (RAO) approach to deliver intensity modulated radiation therapy (IMRT) on the small animal scale using an image-guided small animal irradiator (SmART).

Methods: The SOC features four pairs of orthogonal, double-focused leaves machined from tungsten alloy with tongue-and-groove interfacing. Leaves are driven by Arduino-controlled stepper motors within a 3D-printed housing that mounts onto the SmART. The SOC is controlled with a custom Python GUI that supports treatment plan creation, automated plan delivery, and calibration. Beam commissioning measurements have been acquired on the SmART to accurately predict dose distributions from our RAO treatment planning method. Mechanical and dosimetric testing has been performed on the SOC, and RAO IMRT test plans have been delivered.

Results: Projected leaf width at isocenter is 13mm, with 26mm maximum field size and 1mm minimum beamlet size. An 8 beam spoke shot (to verify alignment and rotational stability) showed <1mm angular shifts. Average leaf face, tongue edge, and groove edge penumbras (80-20%) were 1.66, 1.47, and 1.27mm, respectively. Average maximum transmission between tongue/groove pairs was 4.0% of the full dose. An 8 beam RAO IMRT plan delivered >6Gy to a C-shaped target, sparing the target center to ~2Gy. PDDs, field flatness, and output and off-axis factors were measured for 1-25mm wide fields and incorporated into treatment planning.

Conclusion: A novel small animal IMRT platform has been developed and tested. Beam commissioning has been performed on the SmART and incorporated into a treatment planning system based on Rectangular Aperture Optimization.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by NIH grants U19AI067769 and R21EB025269.


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