Towards two-dimensional brachytherapy dosimetry using plastic scintillator: localization of the scintillation process

Detecting the scintillation light coming from a thin sheet of plastic scint illator (PS) provides a promising fast and precise tissue equivalent method for radiation dose measurements in two dimensions. The successful implemen tation of such technique requires high efficiency, dosimetric tissue equiva lence and high localization of the scintillation process. The last is neede d to assure that the light photons originating from a pixel of the scintill ator sheet correspond to energy deposited in the same pixel. Since no such information is available for PS material with standard or modified chemical composition we have developed two experimental methods for assessing the s cintillation locality by measuring the optical spectra and the scintillatio n light profile (SLP) of PS samples with different thickness. The results o f the two types of measurements are consistent with each other and with a s imple theoretical model of the energy conversion process. We have demonstra ted that comparing the relative intensities of the primary and secondary ph oton peaks in the optical spectra of the scintillator is a sensitive approa ch to determine the delocalization of the secondary photon emission. The ra tio of the number of primary to secondary photons shows strong dependence o n PS dye composition. Two types of plastic scintillator materials were test ed and the advantages of one of them for radiation dosimetry are demonstrat ed. (C) 2000 Elsevier Science B.V. All rights reserved.