Purpose: A preclinical approach to radiation studies analogous to clinical IMRT techniques is developed to provide readily translatable data more directly impactful in guiding clinical practice. Rather than bulk irradiation, individualized treatment plans are created for specific radiation targeting/avoidance in small animals utilizing optimized intensity modulation. These spatially varying beam intensities are achieved using custom 3D-printed compensators.
Methods: In-house software and matRad is used to model the radiation beam from an XRAD225 irradiator and inverse plan optimized beam fluences from arbitrary gantry angles. These beam intensities (bixels) are the basis for generating 3D models with variable thickness corresponding to desired attenuation using a Copper/Polylactic-acid(80/20%) mixture (attenuation coefficient=0.191mmâ?»Â¹). These are fabricated using a fused deposition model 3D printer. The spatial resolution capabilities are investigated using custom-printed test patterns. Modeled after AAPM TG119, a 5-beam inverse plan is created for a miniaturized C-shape test (11.5mm target outer-diameter, 7.0mm target inner-diameter, 2.0mm distance to OAR, and 2.5mm OAR diameter). Corresponding 3D-printed compensators modulate the treatment beam accordingly. Gafchromic film is used to compare planned to delivered dose.
Results: Step function resolution test patterns printed with variable spatial resolution demonstrate that the 3D printer bixel physical resolution limit is ~0.5mm. The C-shape plan 3D printed compensators utilize a physical resolution of 0.7mm, projecting to 1.0mm at isocenter. Accurate production of 3D printed compensators is demonstrated via 80kVp imaging (physical verification) and 225kVp delivery to gafchromic film (dosimetric verification). Good agreement is found between planar dose for planned IMRT delivery and the dose distribution measured in corresponding plane in phantom containing gafchromic film.
Conclusion: This work demonstrates that 3D printed compensators with high-Z/high-density doped plastics provide a simple yet flexible and cost-effective means of generating optimized beam intensity distributions at high-resolution for preclinical radiation studies with IMRT planning/delivery methods analogous to clinical radiotherapy approaches.
Funding Support, Disclosures, and Conflict of Interest: The authors acknowledge support from ACS-IRG-16-222-56 and the Cancer Center Support Grant P30 CA14599.