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Implementation of a Clinical Treatment Planning System for Use with a Small Animal Irradiation System

J Jeong

J Jeong*, Q Chen, R Febo, J Yang, H Pham, J Xiong, J Humm, J O Deasy, G Mageras, Memorial Sloan Kettering Cancer Center, New York, NY

SU-D-144-1 Sunday 2:05PM - 3:00PM Room: 144

Purpose: Current commercially available small animal irradiators provide limited software tools for treatment planning. We report on the implementation of an in-house treatment planning system, Metropolis, for micro-irradiator and compare its capabilities with those of the vendor-supplied system, TPS(XRAD).

Methods: The 225 kV beam of the micro-irradiator was commissioned using both ion chamber and radiographic film (EBT3). Dose calculation in Metropolis was verified by comparing with measured dose in phantom. Starting from a 3D CT image of a tumor-bearing mouse, the same treatment plans were designed in the two systems. In TPS(XRAD), a treatment point was selected on a CT slice, two orthogonal beams were defined based on tumor size on the CT slice, and isocenter depth was computed from a body contour determined by image thresholding. In Metropolis, structures (outer, tumor, and lung) were contoured on CT images, beams were defined based on tumor volume coverage on beams-eye-view (BEV), 3D dose calculation was performed, and plan was evaluated based on dose distribution and dose-volume histogram (DVH).

Results: Measured dose in phantom agreed with Metropolis calculation within 3% for all collimators. The beam-on-times calculated by the two systems agreed within 1% at isocenter. Whereas TPS(XRAD) provides only beam-on-time for each beam, Metropolis capabilities include various image segmentation tools, multimodality image registration, verification of target coverage and normal tissue sparing using BEV, 3D isodose distribution overlaid on CT images, and DVH. DVH inspection of the two-beam treatment plan reveals a tumor dose variation (D₉₅: 388 and D₀₅: 401 cGy) and dose to lung (Dmean: 84 cGy) for a prescribed isocenter dose of 400 cGy.

Conclusion: By implementing a clinical TPS for a small animal irradiator system, both efficient planning and precise plan evaluation become possible, allowing the full potential of advanced micro-irradiator radiation treatment planning to be conducted for pre-clinical experimentation.

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