Author: Benjamin R. Awad, Bulent Aydogan, Howard J Halpern, Erik Pearson, Gage H. Redler, Jordan M. Slagowski, Rajit Tummala, Autumn E. Walter-Denzin, Jimmy Zydlo 👨🔬
Affiliation: University of Wisconsin-Madison Department of Human Oncology, University of Oxford, The University of Chicago, Moffitt Cancer Center, California State University, Fresno, Department of Human Oncology, University of Wisconsin-Madison 🌍
Purpose: Small animal models are crucial in cancer research to develop, validate, and translate basic scientific hypotheses into clinical advancements. This study aims to make small animal intensity-modulated radiotherapy (IMRT) more accessible and reproducible by (1) adapting an open-source treatment planning system (TPS) for preclinical applications and (2) developing a low-cost 3D-printable treatment platform compatible with commercial small animal irradiators.
Methods: A preclinical IMRT platform was developed, consisting of (i) a ring-support that holds five copper-doped plastic compensators, (ii) a SARRP-compatible connecting platform, (iii) an animal bed with 4 mm longitudinal and lateral indexing, and (iv) an anesthesia cone. The system is entirely 3D-printable using standard FDM printers, enabling cross-institutional reproducibility via STL file distribution. The MatRad TPS was modified for inverse kilovoltage treatment planning. Beam models for the X-RAD225Cx and SARRP image-guided irradiators were commissioned using film and ionization chamber measurements of PDD curves and output factors. Tissue-phantom-ratios, output factors, machine geometry, and radial fluence were used to define 0.05 mm pencil beam dose kernels for source-to-surface distances in 1 mm increments. Optimized fluence patterns are delivered by preferentially attenuating the X-ray beam with 3D printed copper-doped plastic compensators. A total variation regularization objective was added to reduce fluence map complexity and improve compensator printability. Copper-doped plastic transmission was measured by irradiating slabs of varying thickness.
Results: Dose calculations in a water phantom matched PDD measurements within 1% for both irradiators. Fluence maps were converted into compensators that fit into a ring-based system attached to the irradiator. Copper transmission was well characterized by an exponential fit (R2=0.997).
Conclusion: A novel system for preclinical IMRT was developed, integrating a validated TPS with a 3D-printed ring-support. This approach eliminates the need for mechanical components, proprietary collimators, or manual compensator switching at different beam angles, enabling high-throughput, efficient, and reproducible treatment delivery.