RADIATION-INDUCED LIGHT IN OPTICAL FIBERS AND PLASTIC SCINTILLATORS -APPLICATION TO BRACHYTHERAPY DOSIMETRY

A small plastic scintillator bonded to an optical fiber has several ch aracteristics that make it promising as a brachytherapy dosimeter, In these dosimeters, scintillation light represents signal, whereas Ceren kov and luminescence light from the optical fiber stem is noise that m ust be subtracted, The dosimeter accuracy can be improved by optically filtering part of the fiber stem light. Spectral measurements were pe rformed to guide the choice of scintillator, fiber, and filter, Spectr al signatures and total luminescence of three scintillators and five d ifferent silica optical fibers, excited by a 8 Ci Ir-192 source, were measured. The total radiation-induced light from the various optical f ibers differed by up to a factor of 5.6, The percentage of fiber-produ ced light due to luminescence varied between 15 and 79%. A fiber with weak emission was used in the dosimeter with BC408S, a scintillator wi th minimum emission wavelength of 400 mm, A 400-nm cutoff UV filter ga ve a factor of two increase in signal-to-noise. The dosimeter response was linear for dose rates varying by at least three orders of magnitu de, representing source-to-probe distances of 0.2-10 cm. Measurement e rrors of the dosimeter compare favorably with other brachytherapy dosi meters.