This research study establishes a repository for imaging data generated during image-guided proton therapy for various pediatric cancers. The data facilitate the estimation of patient positioning uncertainty, the comparison of image guidance methods, and the identification of factors contributing to large setup deviations to improve the accuracy of radiation therapy in the future. Primary Objective To establish a repository of imaging data acquired during the radiation therapy course with linked radiation treatment plans and clinical information from pediatric patients of all cancer types receiving image-guided proton therapy to facilitate secondary and exploratory objectives. Secondary Objectives * To estimate distributions of patient setup uncertainty measured with daily pre- treatment volumetric cone beam computed tomography (CBCT) scans. * To compare patient setup corrections derived based on 2D (orthogonal radiographs) and 3D (volumetric CBCT scans) image guidance. * To assess residual setup errors after CBCT-guided correction based on post- correction repeat CBCT. * To estimate distributions and time trends of patient motion during a radiation therapy course based on weekly pre- and post-treatment CBCT scans. * To identify clinical and treatment factors that contribute to significantly large setup uncertainty and intra-fractional movement in pediatric patients. Exploratory Objectives * To determine variation in patient anatomy using images acquired during the treatment course. * To evaluate the usefulness of on-treatment CBCT scans for detecting daily changes in proton ranges, evaluating deviations from planned tumor dosimetry, and triggering adaptive replanning.