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Ge-doped, P-doped, normal single-mode (SM) and multimode (MM) optical fibers were exposed to Cobalt-60 gamma radiation at dose rates of 0.5 and 3.0 Gy/min, typical radiotherapy dose rates. A CCD-based fiber optic spectrometer was used to measure the real-time absorption spectra of these fibers in the visible region. Experimental results have shown that P-doped fiber is the most radiation-sensitive of the fibers tested. At the wavelength of 502 nm, the radiation-induced loss in P-doped fiber shows a linear relationship with the total dose with no dose-rate dependence. This indicates that dose rates have no influence on a fiber optic dosimeter operating at this wavelength. The radiation-induced losses in normal MM fibers, Ge-doped MM fibers, and Ge-doped SM fibers are shownto be dose-rate dependent. PACS No.: 42.62nBe, 42.81-i