The Feasibility of extending fiber-optic remote in vivo and in situ thermoluminescence (TL) dosimetry to applications in fast neutron radiotherapy will be investigated. To this end, special probes suitable for near-infrared laser beam heating will be developed and tested. They feature small amounts of TLD-700 phosphor (7Li- enriched LiF:Ti,Mg) on the end of quartz fibers, forming thin, flexible, mechanically durable, and re-usable (without removing from inside the phantom or the patient) probes. For discrimination between TL signals due to gamma doses and those produced by large LET particles (neutron-generated recoil proton, alphas and perhaps even nuclei) the well-known generation of deep traps by the interaction of these particles with the TL phosphor must be exploited. This requires further development of the present fiber- optic laser heating technique: production of LiF probe tips that absorb the laser photons and whose protective sheathing does not significantly attenuate knock-on protons, extension of the temperature range to at least 300 degrees C without significant rise in temperature of the outer probe sheathing, and development of microprocessor-controlled beam power delivery for reproducible two-stage heating. The heating beam will be provided by a closed-loop stabilized low cost cw Nd:YAG solid state laser emitting at 1.32 um. Individually calibrated sensor probes of up to several meters in length and less than 2 mm diameter will be fabricated and tested in simulated in vivo applications using the 14 MeV neutron generator at Nuclear Radiation Center of Washington State University and the 50 MeV deuteron-Be neutron generator at the University of Washington.
