Accurate measurement of ionizing radiation dose during radiotherapy planning and treatment is critically important to avoid damage to surrounding tissue. In order to improve the effectiveness of radiotherapy, i.e., maximizing the dose delivered to the cancerous region without damaging surrounding tissue, a real-time in-vivo dosimetry technique would be desirable for directly measuring the delivered dose. The primary method presently known to be suitable for direct dose measurements in vivo is by the use of thermoluminescent dosimeters (TLDs). Unfortunately, TLDs only provide integrated dose information some time after the patient has been irradiated. Therefore, the radiotherapist cannot adjust the exposure in real-time to ensure that the proper dose is delivered to the desired region. Additional limitations of TLDs include their poor dose reproducibility, limited dynamic range and sensitivity, and nonlinear response in certain cases. In order to overcome certain limitations of existing dosimetry systems, a new fiber optic radiation dosimeter has been developed using a patented electron trapping material. This system uses a SrS:Ce,Sm photostimulable storage phosphor which can be exposed to ionizing radiation to produce a population of trapped electrons. The SrS:Ce,Sm material can then be stimulated with 1 micrometers near-IR to produce a visible luminescence directly proportional to the radiation exposure. These processes are optically induced electron transitions and do not involve heating of the SrS:Ce,Sm phosphor, so that measurements are performed at ambient temperatures. The system is further evaluated for the feasibility of fabricating miniature fiber optic probes for real time in-vivo dosimetry.