Page 205 - 00. Complete Version - Progress Report IPEN 2014-2016

Nuclear Science and Technology | Progress Report 205

mogeneous size, shape, and cleavage planes ods was determined. The stability of the dif-
characteristics of transgranular fracture, as il- ferent computerized tomography equipment
lustrated in Fig.5. Furthermore, doping yttria with multiple detectors was also evaluated.
with europium (Y2O3:Eu) led to formation of The Fricke gel solution presented repeatabil-
new defects, which in turn, supplied more ef- ity better than + 5.5% using the O.A. spectro-
fective EPR response. Y2O3:Eu rods exhibited photometry technique and + 3.5% using MRI
linear EPR dose response-behavior from 0.001 technique. The CT equipment presented re-
up to 10kGy. Thermal fading of EPR signal was peatability better than + 0.2%. A skull phan-
less than 20% during 162h. Complete cleaning tom filled with the Fricke gel solution was de-
of EPR signal was achieved by thermal treat- veloped to determine the total collimation of
ment at 1000oC/2h in air. These innovative re- the CT equipment and the dose distribution
sults show that rare earth based ceramics are using the three-dimensional magnetic reso-
promising materials for dosimetry. nance imaging technique. The Fricke gel solu-
tion is easy and relatively quick to prepare,
but care must be taken to avoid contamina-
tion and lose the solution. The results obtained
confirmed the application of this type of do-
simetry to the CT equipment.

Metrology in Radiotherapy

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

Figure 5. SEM images of Y2O3:Eu rods sintered at 1600oC Different phantom materials affect the elec-
for 4h at room atmosphere, (a) general view of ceram-
ic rod; (b) surface microstructure; (c) fracture surface, ex- tron spectrum incident on the detector and it
hibiting cleavage planes in transgranular fracture.
can alter the response of dosimeters to differ-
ent radiation types, so this fact should be con-
External Dosimetry sidered in clinical dosimetry. The TL response
of LiF:Mg,Ti microdosimeters and CaSO4:Dy
Dosimetry in computerized tomography dosimeters were studied for 12 MeV electron
and evaluation of the dose profile beams using PMMA, liquid water and solid
water (SW) phantoms. The dosimeters were
A new method for determination of absorbed irradiated with doses ranging from 0.1 up to
210
doses in computed tomography examinations 5 Gy using a Varian Clinac 0C linear acceler-
was developed using the Fricke gel solution de- ator using a 10 x 10 cm2 field size and 100 cm
veloped at IPEN. Absorbed doses were deter- source-phantom surface distance, with the do-
mined by different methods of analysis: opti- simeters positioned at the depth of maximum
cal absorption spectrometry – O.A., magnetic dose. CaSO4:Dy dosimeters produced at IPEN
resonance imaging - MRI and ionization cham- presented higher TL sensitivity and intrinsic
bers. Lower detection limit, detection sensitiv- efficiency than microLiF:Mg,Ti from Thermo
ity and signal response repeatability of the Scientific dosimeters for all phantoms. For the
Fricke gel solution for the measuring meth- three phantoms studied, the dose response