Small animal IMRT using 3D printed compensators.

PURPOSE Preclinical radiation replicating clinical IMRT techniques can provide data translatable to clinical practice. For this work, treatment plans are created for oxygen-guided dose-painting in small animals utilizing inverse-planned IMRT. Spatially varying beam intensities were achieved using 3D-printed compensators. METHODS AND MATERIALS Optimized beam fluence from arbitrary gantry angles was determined using a verified model of the XRAD225Cx treatment beam. Compensators were 3D-printed with varied thickness to provide desired attenuation using copper/polylactic-acid(CuPLA). Spatial resolution capabilities were investigated using printed test-patterns. Following AAPM TG119, a 5-beam IMRT plan was created for a miniaturized(∼1/8th scale) C-shape target. Electron paramagnetic resonance imaging of murine tumor oxygenation guided simultaneous integrated boost (SIB) plans conformally treating tumor to a base dose(Rx1) with boost(Rx2) based on tumor oxygenation. The 3D printed compensator intensity modulation accuracy/precision was evaluated by individually delivering each field to a phantom containing radiochromic film and subsequent per-field gamma analysis. The methodology was validated end-to-end with composite delivery (incorporating 3D printed tungsten/polylactic-acid(WPLA) beam trimmers to reduce out-of-field leakage) of the oxygen-guided SIB plan to a phantom containing film and subsequent gamma analysis. RESULTS Resolution test-patterns demonstrate practical printer resolution of ∼0.7mm, corresponding to 1.0mm bixels at isocenter. The miniaturized C-shape plan provides PTV coverage (V95%=95%) with organ sparing (OAR Dmax<50%). SIB plan to hypoxic tumor demonstrates utility of this approach (hypoxic tumor V95%,Rx2=91.6%, normoxic tumor V95%,Rx1=95.7%, normal tissue V100%,Rx1=7.1%). The more challenging SIB plan to boost normoxic tumor rim achieved normoxic tumor V95%,Rx2=90.9%, hypoxic tumor V95%,Rx1=62.7%, normal tissue V100%,Rx2=5.3%. Average per-field gamma passing rates using 3%/1.0mm, 3%/0.7mm, and 3%/0.5mm criteria were 98.8±2.8%, 96.6±4.1%, and 90.6±5.9%, respectively. Composite delivery of the hypoxia boost plan and gamma analysis (3%/1mm) gave passing results of 95.3% and 98.1% for two measured orthogonal dose planes. CONCLUSIONS This simple/cost-effective approach using 3D-printed compensators for small-animal IMRT provides a methodology enabling preclinical studies readily translatable into the clinic. The presented oxygen-guided dose-painting demonstrates that this methodology will facilitate studies driving much needed biologic personalization of radiotherapy for improvements in patient outcomes.