Changes in the energy response of a dedicated gamma camera after exposure to a high-flux irradiation.
This work reports the effects of the gain variation of the photomultiplier tubes (PMTs) observed on a cardiac dedicated gamma camera after accidental high-flux irradiation. One detector of this dual-headed 90 degrees-fixed gamma camera was accidentally left uncollimated during a quality assurance procedure on the other detector with a 57Co flood source (259 MBq) and received a non-uniform high flux of 1.9-0.6 Mcps over 25000 mm2 areas for about 30 min. To evaluate the severity and the duration of the perturbation effect on the energy response of the detector, the photopeak position was monitored for about 1 month with a 99mTc point source. The 140 keV photopeak shifted to 158 keV soon after irradiation, reached the correct position after 9 days and moved to a stable value of 132 keV after 15 days. Afterwards, a new energy calibration reset the photopeak position at 140 keV and the correct energy response of the gamma camera. This experience suggests that particular care should be taken to avoid exposures to high radiation fluxes that induce persistent gain shifts on the PMTs of this system.
Matheoud
R
R
Nuclear Medicine Department, Ospedale Maggiore di Milano-IRCCS, Milan, Italy. mednucl1@polic.cilea.it
Zito
F
F
Canzi
C
C
Voltini
F
F
Gerundini
P
P
D002138:Calibration; D015902:Gamma Cameras; D011830:Radiation Effects; D013997:Time Factors