Página 229 - irpa

229 ST 3.2 – Protección radiológica en radiodiagnóstico
(orientada a la tomografía computada)
CARACTERIZATION OF THE MOSKIN DOSIMETER FOR
DIAGNOSTIC X-RAY CT BEAMS
Mendes Pereira, Lenon1 *; Jamil Khoury, Helen1 ; B. Rosenfeld, Anatoly2;
Cutajar, Dean2; Ely Andrade, Marcos1
1 Universidade Federal de Pernambuco. Brasil.
2 University of Wollongong. Australia.
* Responsible author, email:lenonmendes@gmail.com
MOSFET detectors became popular as radiation dosimeters in radiation therapy. The
advantage of MOSFET dosimeters is that they offer real-time dose determination, along with a
very small dosimetric volume. One of its recently designs is called MOSkin, designed by the
Centre for Medical Radiation Physics at the University of Wollongong to measure the real-time
dose delivered to the basal layer (0.07 mm below the skin surface). Some studies have
investigated its use in radiation therapy and it has previously been shown to be suitable for the
measurement of skin doses for this application. However, the use of the MOSkin in Computed
Tomography radiation beam has not being sufficiently investigated. Thus, the aim of this
research was to characterize the response of the MOSkin dosimeter for x-ray CT beams and to
evaluate its application for patient dosimetry and quality control program. Tests were performed
to investigate the sensitivity, energy dependence, reproducibility of the dose response for the
device. All the experiments were carried at Laboratory of Ionization Radiation Metrology (LMRI)
of Federal University of Pernambuco using an industrial x-ray unit. The dosimeter’s response
was evaluated for standard radiation qualities RQT 8, RQT 9 and RQT 10, which simulates the
unattenuated beam used in CT. The results have shown that the MOSkin response was linear
with doses up to 6.9 cGy and reproducible (98.52%). Energy dependence varied up to a factor
of 1.68 among the tested x-ray energies. As expected, the OSkin sensibility was found to
decline with the dose history. For a MOSkin irradiated at a tube potential of 120 kVp the
sensitivity at its end live (Threshold Voltage above 10 Volts) was 4.76% smaller than the
sensitivity at the beginning of its lifetime. Also, pulsed current annealing was proved to be
successful to recover the threshold voltage and sensibility.