Adapting clinical gamma cameras for body monitoring in the event of a large-scale radiological incident

Abstract

After a release of radionuclides, accidental or otherwise, there will be an urgent need to identify members of the general public who have received a significant intake of radioactive material, sufficient to require medical treatment or further investigation. A large number of people could be contaminated in such an incident. For gamma-ray emitting radionuclides this screening could be carried out using gamma camera medical imaging systems, such as those that are present in many large UK hospital sites. By making a number of simple reversible changes such as removal of collimators, these cameras could be employed as useful additional screening instruments as well as an aid in contamination control. A study was carried out to investigate which systems were present in sufficient number to offer wide scale coverage of UK population centres. Nine gamma cameras (eight dual head and one single head) were assessed using point source and bottle mannequin (BOMAB) phantom measurements so that a mathematical model could be developed for use with the MCNPX Monte Carlo radiation transport code. The gamma camera models were assessed for practical seated and supine geometries to give calibration factors for a list of target radionuclides that could be released in a radiological incident. The minimum detectable activities (MDAs) that were achieved for a five minute measurement demonstrated that these systems are sufficiently sensitive to be used for screening of the general public and are comparable to other body monitoring facilities. While gamma cameras have on-board software that are designed for imaging and provide for a gamma-ray energy range suitable for radionuclides for diagnostic imaging (such as Tc), they are not as versatile as custom-built body monitoring systems.

Simulation of an imaging system for internal contamination of lungs using MPA-MURA coded-aperture collimator

“…In the second step, the W, X, Y, and Z sub-regions were transformed into E, F, G, and H, respectively, by rotating 180°, as shown in (4). where…”

“…The main nuclides released included Mo-99 (140.5 keV), Ce-141 (145 keV), Ce-144 (133 keV), I-131 (365 keV), Cs-137 (662 keV), Cs-134 (604 keV, 795 keV), Zr-95 (724.1 keV, 756.7 keV), Mn-54 (834.85 keV), and Co-60 (1173 keV, 1332 keV), [1][2][3] and enter the human body through breathing, drinking, eating, and open wounds. Therefore, it is imperative to urgently carry out the screening of internal radioactive contamination as early as possible after a nuclear accident [4][5][6][7] .…”

Medical gamma cameras in radiological emergency preparedness: determination of calibration factors and MDA for the GE Discovery NM/CT 670 Pro

“…The efficiency in detecting higher photon energies decreases rapidly with decreasing thickness of the NaI crystal, and several radionuclides of concern in RN events emit gamma rays of higher energies, e.g. 662 keV from 137 Cs, and 1173 keV and 1332 keV from 60 Co. Another problem is the energy window allowed in commercial gamma cameras, which is often restricted to below 550 keV [6].…”

“…Several studies have shown that, despite the above-mentioned drawbacks, the use of gamma cameras as a complement to WBCs for the estimation of the activity of the radionuclides that can be expected following an RN event, is feasible [6][7][8][9][10]. In the case of an RN event, the imaging capability is of minor interest compared to the ability to quantify the internal contamination.…”

“…The efficiency of gamma cameras can be increased by removing the collimator, which is placed in front of the detector to reduce scattered radiation from the subject in order to enhance the imaging capability of the camera. This allows a sufficiently low MDA to be measured during a reasonably short measuring time [6][7][8].…”