Teste | Abstract: 90-1 | ||||
Abstract:Ionizing radiation is widely used in healthcare, requiring strict dose control to avoid adverse effects or even accidents. Quality control of equipment is necessary to ensure the proper functioning of services and the protection of individuals. Electron spin resonance (ESR) dosimetry is well established in clinical applications and high-dose applications [1]. Among the advantages of alanine as a dosimeter are its low energy dependence, linear response with dose, and tissue equivalence, eliminating the need for the use of correction factors [2]. This shows that the use of ESR dosimetry with alanine in quality control of irradiation procedures of biological materials, such as blood irradiation, is advantageous [3]. Hence, in this work L-alanine dosimeters were used in quality control of a blood irradiation unit. The dosimeters were calibrated with a 137Cs source, with dose rate of 1.524 Gy/min, in dose values convenient for the application. Signal acquisition was performed with a Jeol FA-200 X-band spectrometer using the following parameters: central field of 336.9 mT, power of 5 mT, scan time of 1 min, and scan width of ±10 mT. The signal used to calculate the dose is obtained from the peak-to-peak amplitude of the spectrum and is normalized by the spectrometer gain and the mass of the dosimeter. It was thus possible to obtain group calibration along with the dose-response curve. An ABS (acrylonitrile butadiene styrene) phantom was 3D-printed with a sliced cylindrical geometry. Each of the 15 slices has 8 holes for the L-alanine dosimeters, allowing for depth dose mapping. The phantom was built based on a model already used locally in quality control and was adapted for the L-alanine dosimeter. It allows for the evaluation of the dose and dose uniformity delivered to blood bags throughout the irradiation cylinder. The study was conducted in a blood center where a dose of 25 Gy to the center of the volume was requested. After obtaining the signal and calculating the dose with the L-alanine dosimeters, dose delivery peaks of 44.5 Gy were observed at the edges of the volume and minimum dose of 23.2 Gy were delivered in the center of the volume, the average dose obtained was 35.3 Gy. The dose delivery in the center of the volume was 7.2% lower than the requested value. The hot and cold spots obtained agree with the geometry of the irradiated volume as the beam attenuation causes a reduction in the dose delivered at the center. The difference in dose delivery of 21.3 Gy complies with the standards established by the National Health Regulatory Agency (ANVISA), which determines that no spot should receive less than 15 Gy and more than 50 Gy, and the average dose must be larger than 25 Gy [4]. It can be concluded that the irradiator is in good operating condition. Keywords: blood irradiation , ESR dosimetry , quality control |