Investigation of the dosimetric characteristics of radiophotoluminescent glass dosimeters for computed tomography

Ključni zadatak dozimetrije je određivanje apsorbirane energije u tvari koja je bila izložena ionizirajućem zračenju. Postoji niz dozimetrijskih sustava, ali u ovom radu je upotrijebljen dozimetrijski sustav koji radi na principu radiofotoluminiscencije (RPL) fosfatnog stakla dopiranog srebrom. Radiofotoluminiscenija je pojava emitiranja vidljive svjetlosti iz ozračenog materijala kada se pobudi s UV svjetlosti. U radu su upotrijebljeni RPL dozimetri tipa GD-352M koji se sastoje od staklenih štapićastih detektora i plastičnih držača u kojima se nalazi filter za smanjenje ovisnosti o energiji. U ovom radu najprije je ispitana ujednačenost, individualna osjetljivost, ponovljivost očitanja i reproducibilnost RPL dozimetara nakon zračenja na izvoru 137^Cs (0,661 MeV) u Sekundarnom standardnom dozimetrijskom laboratoriju Instituta Ruđer Bošković. U drugom dijelu rada napravljena su mjerena apsorbirane doze na uređaju za računalnu tomografiju stožastim rendgenskim snopom (engl. cone beam computed tomography, CBCT) koji je integriran uz uređaj Leksellov gama nož (engl. Leksell Gamma Knife) u Kliničkom bolničkom centru Zagreb s RPL dozimetrima i ionizacijskom komoricom. Rezultati istraživanja pokazali su malu razliku u individualnoj osjetljivosti dozimetara, dobru ujednačenost, mogućnost višestrukog očitanja dozimetra bez promjene u apsorbiranoj dozi te dobru reproducibilnost. Mjerenja s RPL dozimetrima u računalnoj tomografiji pokazala su dobro slaganje apsorbirane doze u CTDI fantomu s mjerenjima ionizacijske komore i s tabličnim vrijednostima.The main task of dosimetry is the determination of absorbed dose in matter that has been exposed to ionizing radiation. There are variety of dosimetry systems, but the main focus of this work is dosimetry system based on radiophotoluminescence (RPL) phenomenon of silver activated phosphate glass. Radiophotoluminescene is the emission of visible light from irradiated material when it is exposed to UV light. The RPL dosimeters (type GD-352M) characterized in this study consists of glass rod like detectors packed in a plastic holder which contains energy compensation filter. In the first part of the study uniformity, individual dosimeter sensitivity, repeatability of reading and reproducibility were tested after irradiation in the Secondary Standard Dosimetry Laboratory at Ruđer Bošković Institute using 137^Cs (0.661 MeV) source. The second part of the study was performed at Universtiy Hospital Zagreb by measurments of absorbed dose on cone beam computed tomography (CBCT) device (which is a part of Leksell gamma knife) with RPL dosimeters and ionisation chamber. Experimental results show small differences in individual dosimeter sensitivity, good uniformity, possibility of repeated readout without change in absorbed dose and good reproducibility. Measurments with RPL dosimeters in computed tomography show good agreement of absorbed dose in CTDI phantom with ionization chamber measurments and tabulated values