Page 58 - PR 2014 2016 07 Nuclear Science and Technology

200 Nuclear Science and Technology | Progress Report

by thermal treatment at 1600°C for 4h. As chambers. Lower detection limit, detection sen-
sintered yttria based rods exhibited dense sitivity and signal response repeatability of the
surface microstructure, homogeneous size, Fricke gel solution for the measuring methods
shape, and cleavage planes characteristics of was determined. The stability of the different
transgranular fracture, as illustrated in Fig.34. computerized tomography equipment with
Furthermore, doping yttria with europium multiple detectors was also evaluated. The Fric-
(Y O :Eu) led to formation of new defects, ke gel solution presented repeatability better
2 3
which in turn, supplied more effective EPR re- than + 5.5% using the O.A. spectrophotometry
sponse. Y O :Eu rods exhibited linear EPR dose technique and + 3.5% using MRI technique. The
2 3
response-behavior from 0.001 up to 10kGy. CT equipment presented repeatability better
Thermal fading of EPR signal was less than than + 0.2%. A skull phantom filled with the
20% during 162h. Complete cleaning of EPR Fricke gel solution was developed to determine
signal was achieved by thermal treatment at the total collimation of the CT equipment and
o
1000 C/2h in air. These innovative results show the dose distribution using the three-dimen-
that rare earth based ceramics are promising sional magnetic resonance imaging technique.
materials for dosimetry. The Fricke gel solution is easy and relatively
quick to prepare, but care must be taken to
avoid contamination and lose the solution. The
results obtained confirmed the application of
this type of dosimetry to the CT equipment.

Metrology in Radiotherapy

TL response and intrinsic efficiency of
dosimeters irradiated using different phantoms
in clinical electron beam dosimetry

Different phantom materials affect the elec-
Figure 34. SEM images of Y O :Eu rods sintered at 1600°C
2 3
for 4h at room atmosphere, (a) general view of ceram- tron spectrum incident on the detector and it
ic rod; (b) surface microstructure; (c) fracture surface, ex- can alter the response of dosimeters to differ-
hibiting cleavage planes in transgranular fracture.
ent radiation types, so this fact should be con-
sidered in clinical dosimetry. The TL response
External Dosimetry of LiF:Mg,Ti microdosimeters and CaSO :Dy
4
dosimeters were studied for 12 MeV electron
Dosimetry in computerized tomography beams using PMMA, liquid water and solid
and evaluation of the dose profile water (SW) phantoms. The dosimeters were

irradiated with doses ranging from 0.1 up to
A new method for determination of absorbed 5 Gy using a Varian Clinac 0C linear acceler-
210
2
doses in computed tomography examinations ator using a 10 x 10 cm field size and 100 cm
was developed using the Fricke gel solution source-phantom surface distance, with the do-
developed at IPEN. Absorbed doses were de- simeters positioned at the depth of maximum
termined by different methods of analysis: dose. CaSO :Dy dosimeters produced at IPEN
4
optical absorption spectrometry – O.A., mag- presented higher TL sensitivity and intrinsic
netic resonance imaging - MRI and ionization efficiency than microLiF:Mg,Ti from Thermo

Instituto de Pesquisas Energéticas e Nucleares