Aqueous-based photothermographic materials that are sensitive to visible or X-radiation contain X-radiation sensitive phosphors in association with specific chemically sensitized tabular silver halide grains. The silver halide grains comprise at least 70 mol % bromide ,based on total silver halide, have an average thickness of at least 0.02 µm and up to and including 0.10 µm, an equivalent circular diameter (ECD) of at least 0.5 µm and up to and including 8 µm, and an aspect ratio of at least 5:1. These materials can be imaged in any suitable fashion but preferably they have one or more photothermographic layers on both sides of the support and can be imaged using X-radiation with or without an associated phosphor intensifying screen.