FEASIBILITY STUDY OF FIBER-OPTIC FAST NEUTRON DOSIMETRY

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 CENTIGRADE 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.