In this study, we investigated the radiation-induced optical responses of NaCaPO4 ceramics doped with Ag (0.1, 0.3, 1.0, 2.0, and 3.0%). After irradiating the samples with X-rays, the photoluminescence (PL) recorded under UV excitation increased slightly at low doses (≤~100 mGy), which is indicative of the radio-photoluminescence (RPL) phenomenon. At higher doses (≥~1 Gy), the PL intensity decreased. Prompted by the high-dose PL quenching, we measured the reflection spectra, which revealed that absorption bands were induced by X-ray irradiation and that their intensities increased with absorbed dose. In particular, the band centered at ~400 nm, attributable to the surface plasmon resonance of Ag nanoparticles, grew monotonically with absorbed dose. The 0.3% Ag-doped sample provided an exceptionally broad dynamic range from ~1 mGy to 100 Gy. These results indicate that the Ag-doped NaCaPO4 ceramic is more appropriately regarded as a radiochromic material than as an RPL phosphor and is well suited to applications requiring wide-range dose monitoring.