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Treatment Planning System for Intensity Modulated Small Animal Radiotherapy Realized with a Movable Rectangular Collimator

H Liu*, C Shen , Y Gonzalez , X Jia , University of Texas Southwestern Medical Center, Dallas, TX


(Tuesday, 7/16/2019) 3:45 PM - 4:15 PM

Room: Exhibit Hall | Forum 4

Purpose: Using collimators of fixed sizes and shapes, it is difficult for the current standard small animal irradiators to effectively spare organs at risk (OARs). To improve treatment quality, we developed a treatment planning system to achieve intensity-modulated radiation therapy (IMRT) using a movable rectangular collimator that is typically available on current irradiators.

Methods: We computed dose deposition matrix using our GPU-based fast Monte Carlo dose calculation engine. The small animal IMRT treatment planning is formulated as a direct aperture optimization problem under the constraint of only using rectangular aperture shapes. A column generation algorithm is employed to solve the optimization problem to determine a series of rectangular aperture shapes and corresponding beam-on time. For each beam angle, we further determined the most efficient delivery sequence. Specifically, we constructed a graph with vertices being the apertures and links being transition time between apertures. The most efficient delivery sequence corresponds to the shortest-path in the graph. We evaluated the developed system on a water phantom case and two mouse cases (A and B) with lung tumors. Plan quality and delivery efficiency were compared between the IMRT plan and the plan based on cone collimators.

Results: In all cases, when IMRT plan and cone-based plan are normalized to the same target coverage, OARs were spared much more effectively in IMRT plans. The average beam-on time of IMRT plan for the mouse cases was ~80s, approximately doubling that of cone-based plans because of reduced beam output under the apertures. The IMRT plan requires additional ~7s of collimator motion time.

Conclusion: We have developed an inverse IMRT treatment planning system for small animal irradiation using a movable rectangular collimator. The IMRT plan quality surpasses that of the standard cone-based plan. Treatment delivery time is prolonged mainly due to reduced beam output under the collimation.

Funding Support, Disclosures, and Conflict of Interest: This project is supported in part by NIH/NCI grant R37CA214639.


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