Detection limits and quantification of 60Co with gamma camera and handheld gamma detectors in human phantoms

Abstract: In an emergency situation where radioactive material has been spread to the environment and large groups of people have been internally contaminated there is a need for rapid examination of the activity contents in those persons. The specific purpose of this work is to explore methods for rapid in-vivo determination of 60Co in humans using equipments not dedicated to whole-body counting, in order to find rapid alternative to whole-body counting in low background localities. Different types of detectors and their potential for in-vivo activity determination have therefore been investigated by using different sized human phantoms. The purpose is also to determine the lowest detectable activity and to find calibration factors for different detectors, phantom sizes and uptake volumes. The detectors studied were a clinical gamma camera and different handheld gamma detectors. The gamma camera was a 96 Simens Multispect with a field of view of 21 x 15 in., used for clinical examination by the Department of Clinical Physics, Malmö. In addition to determination of calibration factors and detection limits the task was also to investigate if it is possible to image 60Co uptakes in humans with a gamma camera.The measurement was carried out by charging phantoms of different sizes with 60Co-sources in the form of rods of ion exchange mass with a diameter of 6 mm. The inserted amount of 60Co activity was successively built up in steps and for every increase of activity the count rate registered by the detectors was recorded. The count rate vs. the inserted activity of 60Co was plotted and calibration factors and the detection limit of the given uptake geometry and detector set-up was estimated using linear regression of the plots. By placing a 60Co source in the gamma camera set-up and use different energy window the possibility of using the gamma camera for imaging was tested. The results show that the gamma camera and handheld gamma detectors can potentially be used for quantification of uptakes of 60Co in humans. The detections limit for the gamma camera was approximately two to four times lower then for handheld radiations instruments, and approximately ten times higher than for the low background whole-body counter at the Department of Medical Radiation Physic. It also appeared possible to obtain imaging with the gamma camera for 60Co if using non-primary photon peaks.