Joseph B. Schulz Laszlo Zalavari Paulina Gutkin Yi Peng Wang Karl K. Bush Lei Wang Sarah S. Donaldson Billy W. Loo Susan M. Hiniker Lawrie Skinner ^*

• Department of Radiation Oncology, School of Medicine, Stanford University, Stanford, California, United States

Purpose: This paper discusses an advanced version of our Audio Visual Assisted Therapeutic Ambience in Radiotherapy (AVATAR) radiolucent display systems designed for pediatric radiotherapy, enabling anesthesia-free treatments, video communication, and biofeedback. The scope of the AVATAR system is expanded here in two major ways: (i) through alternative mounting systems to accommodate a broader range of radiotherapy machines (specifically to fit robotic-arm and toroidal geometry photon radiotherapy and proton radiotherapy systems) (ii) through additional hardware to provide video-calling, optimized audio for clear communication, and combined video inputs for biofeedback, translation, and other advanced functionalities. Methods and Materials: Since robustness requires strong parts and radio-transparency requires thin, light parts, 3D printing was used to rapidly prototype hollow structures and to iteratively improve robustness. Two system designs were made: one that mounts superior, and another that mounts inferior to the patient's head. Radiation dose measurements and calculations were conducted to assess dose perturbations at surface and depth due to the screen. Results: For 6 MV volumetric modulated arc therapy (VMAT) plans, with and without the screen, the mean and maximum dose differences inside the PTV were 0.2% and 2.6% of the 200 cGy prescription respectively. For a single static beam through the screen, the maximum measured excess surface dose was 13.4±0.5%, and the largest measured dose attenuation at 5 cm water-equivalent depth was 2.1±0.2%. These percentages are relative to the dose without the screen at those locations. Conclusions: The radiolucent screen systems provided here are shown to give minimal dosimetric effects on mega-voltage VMAT photon treatments. For static beams, however, surface dose effects should be considered when these beams pass through the thickest components of the screen. Design files are also provided.