MATERIALS FOR THERMOLUMINESCENT DOSE DETECTORS AND PHOTON RADIATION ENERGY DETECTORS INTENDED FOR INTERCOMPARISON PROCEDURES OF RADIATION-THERAPY UNITS

Composite thermoluminescent (TL) materials characterized by different TL sensitivity to energy of photon radiation, namely, double-component mixtures of finely dispersed ingredients: thermoluminescent phosphor (LiF or CaS04: Dy) and nonluminescent material (salts with various Zeffvalues) have been described. The TL sensitivity of such TL composites was demonstrated to depend upon Zeff values inherent to separate components and upon their concentration ratio in the mixture. Within the range of x-ray energy values from 10 to 120 keV, the LiF-based materials containing Li2C03 as nonluminescent material were dosimetrically equivalent to soft tissues. The availability of powder-like TLD materials containing 65% LiF+35% Li2C03 can definitely serve the basis for extending the application area for the well-known procedure adopted by IAEA/WHO for comparative testing of x-ray therapy units with HVL<0.5 mm Cu and for starting the intercomparison of units intended for superficial x-ray therapy. The use of the dose detectors based on TLD of 35% LiF+65% Li2C03 composition in orthovoltage x-ray therapy units excludes the necessity for introducing corrections for the dependence of detector's readings on energy levels. LiF- and CaS04:Dy-based TL materials containing PbS04 as a nonluminescent material are, by a factor of 10, more sensitive to energy variations than other known thermoluminescent phosphors. With the application of TLD based on above materials into two-detector systems intended for determining £eff values of x-ray radiation, the ambiguity of readings in low-energy region has been eliminated, whereas the range of measurement appeared to be significantly expanded. © 1994, American Association of Physicists in Medicine. All rights reserved.