A canine head phantom for quality assurance in multiport microbeam radiation therapy: animal phantom fabrication and dosimetry protocol

This study aims to develop canine radiotherapy phantoms and a dosimetry protocol for synchrotron microbeam radiation therapy (MRT). Two canine head phantoms were designed based on computed tomography (CT) image sets obtained from veterinary patients. Polylactic acid polymer and calcium sulfate hemihydrate plaster were used to radiologically simulate soft tissue and bone. Fused deposition modeling 3D printing was used to fabricate the external geometry of the head phantoms. CT images of the phantoms were acquired to measure its CT number profile and to create treatment plans. Using a 4 Tesla superconducting multipole wiggler field and in vacuo filters, synchrotron beam was delivered as broad-beam and as microbeam arrays at the imaging and medical beamline of the Australian Synchrotron. The Monte Carlo simulated dose using a hybrid EclipseTM treatment planning system (TPS) was compared to the experimental measurements. The head phantoms offer a realistic three-dimensional canine head geometry and CT numbers mimicing soft tissue and bone. Various types of detectors and biological samples can be accomodated, using a series of customizable rectangular inserts. The measured accumulated doses for microbeam irradiation were within +/- 2% of the TPS doses, while all the other measured doses were within +/- 10% agreement with the TPS doses. The TPS, phantom positioning, and detector uncertainties contributed to the measurement discrepancies. The 3D printed canine phantoms were shown to be useful dosimetry tool for synchrotron MRT end-to-end quality assurance. The development of canine phantoms and dosimetry methodology are critical for the treatment plan optimization required in future veterinary studies. Both the phantoms and the dosimetry protocol are valuable tools in future veterinary MRT trials.