Effects of Simultaneous Photon and Thermal Bleaching on Sensitivity of Medical Fiber Optic Dosimeters Doped With Either Ge, P or Er

Abstract

Today, high energy electro-magnetic radiation or charged particles are widely used for medical treatments of certain patients. Precise prediction and measurements of energy deposition of any types of radiation on tissue is the most important portion of radiation therapy. In this research, special fiber optics doped either with Phosphor (P), Germanium (Ge) or Erbium (Er) with various doping concentrations are used as a radiation sensor and irradiated by Co-60 source with 169 cGy per minute for 3 minutes. During irradiation, the Radiation Induced Attenuation (RIA) was measured as a function of radiation dose rates. A non-linear behavior of RIA was observed for Ge doped fiber optics at various laser frequencies. However, fiber optics doped with P or Er show a linear attenuation at 532 nm laser during irradiation. In addition, to maintain the sensitivity of fiber optic dosimeters as a function of exposure time, the residual radiation was bleached with photon, thermal energy and both techniques simultaneously. Bleaching photon sources were three types of lasers with wavelengths 445nm (300mW), 532nm (500mW) and 808nm (1000mW). After fiber optics were irradiated and RIA measured as a function of radiation dose, they bleached to recover original sensitivity condition of dosimeters. This process repeated ten times to analyze the sensitivity of fiber optic dosimeters.