Efficiency correction factors of an ACCUSCAN whole-body counter due to the biodistribution of 134Cs, 137Cs and 60Co

Abstract

The efficiency calibration of whole-body counters (WBCs) for monitoring of internal contaminations is usually performed with anthropomorphic physical phantoms assuming homogeneous activity distribution. Besides the inherent limitations of these phantoms in resembling the human anatomy, they do not represent a realistic activity distribution, since in real situations each incorporated radionuclide has its particular biodistribution after entering the systemic circulation. Moreover, the activity content in the different organs and tissues comprising the biokinetics is time dependent. This work aims at assessing the whole-body counting efficiency deviations arising from considering a detailed voxel phantom instead of a standard physical phantom (BOMAB) and at evaluating the effect of the anatomical differences between both phantoms. It also aims at studying the efficiency considering the biodistribution of a set of radionuclides of interest incorporated in the scope of environmental and occupational exposures (inhalation and ingestion) and at computing the time-dependent efficiency correction factors to account for the biodistribution variation over time. For the purpose, Monte Carlo (MC) simulations were performed to simulate the whole-body counting efficiencies and biokinetic models were used to estimate the radionuclides' biokinetic behaviour in the human body after intake. The comparison between the efficiencies obtained with BOMAB and the voxel phantom showed deviations between 1.8 and 11.7 %, proving the adequacy of the BOMAB for WBC calibration. The obtained correction factors show that the effect of the biodistribution in the whole-body counting efficiency is more pronounced in cases of acute activity uptake and long-term retention in certain organs than in cases of homogeneous distribution in body tissues, for which the biokinetics influence can be neglected. This work further proves the powerful combination of MC simulation methods using voxel phantoms and biokinetic models for internal dosimetry studies.

Selection of an optimal macrocyclic chelator improves the imaging of prostate cancer using cobalt-labeled GRPR antagonist RM26

“…1). Uniform activity distribution was observed at both time points with somewhat elevated uptake in liver that was in good agreement with previously published data 17 .…”

Use of Iodine-131 to Tellurium-132 Ratios for Assessing the Relationships between Human Inhaled Radioactivity and Environmental Monitoring after the Accident in Fukushima

“…This estimation was achieved by introducing a physiochemical compartmental treatment in the calibration. Namely, we performed a 3-pattern calibration to determine 131 I body burdens as follows: first, the simplest, was the compartment calibration; hence the only BOMAB data was used for this homogeneous whole body calibration [ 7 , 15 ]. Second was two-compartment calibration, which presumed that the gamma rays came from the thyroid and homogeneous whole body (the rest of the compartments) independently.…”

“…To determine the residual activity ratios of each compartment to the total 131 I body burden in the biokinetic calibration, self-consistent approach, together with the time-dependent correction efficiency factors concept [ 15 ] was applied. In this technique, an estimated thyroid residual activity of a subject was individually calculated repeatedly, using the physiological biokinetic model [ 16 ], until the result achieved was consistent with the thyroid counter measurement [ 2 ].…”

Monte Carlo simulation of a whole-body counter using IGOR phantoms

“…Various MC computer codes have been used so far: 'FLUktuierende KAskade' (FLUKA) (25) , 'Monte Carlo N-Particle' (MCNP) (26 -33) , 'Electron Gamma Shower' (EGS) (5,6,34,35) , 'PENetration and Energy LOss of Positrons and Electrons' (PENELOPE) (32) , 'GEometry ANd Tracking' (GEANT) (36) or local codes developed ad hoc (37) . MC calculation has been used to compare different mathematical phantoms used in WBCs (10,26,27,29,31,35,38) or to compare the measurements obtained with a physical phantom with the results obtained by a simulated version of this phantom (5,6,30,35,37) . MC calculations are also used to investigate how the counting efficiency of the WCB depends on various parameters of the system that may be sources of uncertainty, such as the difference between the shape and size of the person to be monitored and the phantom, the measuring geometry, notably the position of the detector, the phantomdetector distance, the distribution of the radionuclides in the body, etc.…”