131 I) has been used for diagnosis and therapy in Nuclear Medicine Centers in Brazil for more than 50 years.The present study aims to investigate the impact of the counts density and the reconstruction parameters in the calibration factor determination and in the image quantification, considering the reality of Brazilian dosimetry studies.For this task, images were quantified using calibration images with high and low counts density and reconstructed adopting two different parameters approaches, usually employed in patients images. SPECT quantification results presented in this work follow other previous 131 I SPECT studies and suggest that, due to the long time interval between the first e last images, as required by the Brazilian guideline, the image quantification accuracy can be improved if the counts density of calibration images is considered.

Many research groups have studied nuclear medicine image quantification to improve its accuracy in dose estimation. This work aims to evaluate the influence of the source calibration position for absorbed dose calculation for a I-NaI therapy using Monte Carlo (MC) simulations. The calibration approach consisted of a cylindrical phantom filled with water. A cylindricalI source with 361.1 ± 3.6 kBq ml was positioned at the center of the phantom and its outer part. Images were acquired with 150 00 counts per projection image acquired with SPECT detector (high counts density-HCD) and 3000 counts per projection (low counts density-LCD). MC simulations, performed with GATE code, were validated by comparing the S values of a water sphere uniformly filled with I, as from the sphere model of OLINDA/EXM 1.1. Calibration factors deviation between central and peripheral calibrations is more significant for HCD (18.3%) than for LCD images (3.7%). The 3D dose distribution map obtained from GATE resulted in a dose factor equal to 1.5 × 10 mGy/(MBq.s). For both HCD and LCD images, the commonly used approach, which employs the central source calibration to obtain the dose from a peripheral source, resulted in dose overestimation. Results suggest that organ dose calculation can be improved considering the organ position in the field of view. Finally, patients' radiation protection in dosimetry studies could be improved considering the calibration source position, due to the superior accuracy in dose calculation.

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s x KOTICÊ .'Vvlffff jf f fflll BEPOHT ABE lttf«B?,f c e ^ ^s be«ii reprodyced from Me Hext 2 | ./aflablp coaf to permit the broadest •f ^ ABSTRACT tfwslMe avaifaWlity. c j. >-Airborne particulates were collected through filters in occupational £> =-areas of the uranium mining and Killing complex located in Poeos de Caldas, LU C _o ^ Brazil. The filters were analysed by sdcroPIXE {particle induced x-raŷ j. emission) combined with Rutherford Backscattering ! (?.SS) of the incident u sj * protons. The results are discussed in the paper. * Work supported by U.S. DOE Contracts 0E-ACO2-76EV-OO 719 (ASP, MEK) and DF-AC02-76CH-00116 (XNt7).

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