An integrated 3D printed radioluminescent-based phantom for quality assurance on a robotic-arm linac.

Objective . To develop, characterize and improve upon a high-resolution 3D printed radioluminescence-based imaging phantom for quality assurance (QA) of a robotic arm linear accelerator. Approach . A phantom was constructed which consisted of a scintillating sheet, fiducial markers, a low-cost complementary metal-oxide semiconductor camera and a 3D printed light-tight enclosure. The camera, equipped with a 12 mm lens, was angled 45 degrees from the horizontal axis with a direct line of sight of the scintillating sheet. A perspective image transformation with optical distortion correction was employed to obtain beam's eye view images for different collimators. Beam profiles, Iris™ field size, multileaf collimator leaf positioning and central laser-radiation field coincidence QA tests were performed and compared against data obtained with gafchromic film. The phantom's short-term stability, sensitivity to changes in output, field size and leaf positioning were also assessed. Main Results . The limiting resolution of the optical system was measured to be ∼0.26 mm. Field size, as measured by the radioluminescence system for Iris apertures, agreed to within 0.2 mm of the values measured using film. The imaging system was sensitive to field size changes well below 0.2 mm and output changes as small as 1 monitor unit (MU). For the optical setup, the mean leaf deviation error for banks X 1 and X 2 was 0.21 and 0.17 mm at 800 mm source to axis distance, whereas the mean difference for the film dataset was 0.16 mm and 0.22 mm for banks X 1 and X 2, respectively. The optical system was able to detect leaf positioning errors as small as 0.2 mm. Compared with film data, excellent agreement was seen for relative central axis beam profiles for 10 mm and 5 mm beams. Significance . The phantom presented here is an alternative to film and electronic portal imager devices, due to its low-cost, portability, and high spatial and temporal resolution.