Project Summary The study of the preclinical animal models included in all four Projects plays a critical role to investigate the overall hypothesis that Proton/Carbon Particle FLASH Radiotherapy is superior to Standard Particle Radiotherapy in protecting normal tissues while maintaining equipotent malignant growth control. The extrapolation of robust preclinical data in these experimental settings relies heavily on the unbiased assessment of specific histopathological parameters to investigate the biological effects of FLASH particle radiotherapy as compared to Standard particle radiotherapy on designated neoplastic lesions and adjacent normal tissues. The Comparative Pathology Core (CPC; Core C) will provide its expertise contributing to the planning, evaluation, and interpretation of the pathology endpoints of the animal experiments included in the Projects. As a PennVet clinical laboratory, Core C importantly follows standardized working protocols with strict QA/QC procedures. The histopathology service offered by Core C will ensure accurate collection, proper preservation, timely processing, and staining of the animal specimens. Core C will provide the necessary technical support and submissions of tissue samples will follow a prioritized route. In addition to standard histopathology, Core C will also develop and validate tailored approaches to investigate and quantify tissue changes specifically associated with RT such as fibrosis, intralesional distribution of inflammatory/immune cell populations, expression of markers to evaluate epithelial barrier integrity, etc. The board-certified veterinary pathologists of Core C will deliver expert evaluation and unbiased interpretation of the pathology endpoints. Objective and reproducible quantification of tissue changes in response to the diverse RT modalities will be guaranteed by the application of validated scoring systems and the utilization of software-based algorithms for digital pathology and image analysis. Core pathologists have advanced training in digital imaging pathology from Leica pathology systems. Moreover, Dr. Assenmacher has collaborated with Leica in the development of analysis tools, lending him particular experience in the analytic modules of the digital pathology system.