We have measured radiation ((gamma) ray) induced loss of P- doped and Ge-doped fibers with different dopant concentrations and core diameters for different dose rates. The following conclusions can be obtained from our experiment: (1) The fibers we tested (P and Ge doped) have no evident recovery after (gamma) ray radiation. (2) No evident photo-bleaching effect had been observed by irradiating the fiber with diode laser of wavelength 630 micrometer. (3) Optical fiber with higher dopant concentration does not mean more sensitive. (4) For fiber length as short as 0.3 m, the sensitivity of P-doped fiber (0.6 - 0.8 dB/m for total dose of 4 Gy) is sufficient for the measurement of dose range for patients.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.