Program Information
Feasibility of a High Throughput Megavoltage Small Animal Irradiation Technique for Localized Cranial Irradiation
J Carroll*, S Floyd , J Adamson , Duke University Medical Center, Durham, NC
Presentations
WE-RAM3-GePD-TT-2 (Wednesday, August 2, 2017) 10:30 AM - 11:00 AM Room: Therapy ePoster Theater
Purpose: There is growing interest in applications of Cerenkov from megavoltage radiotherapy to imaging and drug activation. However, many animal irradiation systems use kV x-rays which lack Cerenkov emissions. We investigate feasibility for high-throughput small animal brain megavoltage irradiation using a clinical accelerator with High Definition MLCs (HD-MLCs).
Methods: We utilized the Eclipse planning system with Anisotropic Analytical Algorithm, 1mm dose grid, and a Varian STX with HD-MLCs (2.5mm width). We investigated minimum treatable target size by creating a small animal sized phantom with three PTVs (10, 5, & 2.5mm diameter). In addition, we created treatment plans for a mouse CT, treating either the whole left hemisphere or a 2.5mm PTV within the left hemisphere. Treatment planning techniques included dynamic conformal arcs (DCA) and volumetric modulated arc therapy (VMAT), each with 5 equally spaced arcs for varying margins (0.0-2.0mm range in 0.5mm increments). Conformity index (CI) and gradient index (GI) were calculated. Finally, in order to develop an efficient and effective method for mouse immobilization, various iterations of immobilization devices were designed using Autodesk Fusion 360 and printed using an Ultimaker 2.
Results: DCA plans with no MLC margins had optimal CI and GI, while also delivering the smallest median dose to the ipsilateral hemisphere, with contralateral hemisphere median dose of 23% of prescription dose for the 2.5mm target. The VMAT plan targeting the left hemisphere decreased CI, increased GI, and decreased median dose to the right hemisphere, but the VMAT plan targeting the 2.5mm PTV had the opposite effect.
Conclusion: Our work indicates that a high-throughput small animal irradiation technique is feasible down two a 2.5mm diameter PTV. Future work will include optimizing efficiency by investigating applying a single-isocenter technique for multiple-targets, finalizing a design for an easily reproducible and efficient 3D-printed immobilization device, and validating delivered dose.
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