Calibration and validation of a quality assurance system for 90Sr/90Y radiation source trains

A quality assurance system (OPTIDOS, PTW-Freiburg) developed for dose rate verification of Sr-90/Y-90 radiation source trains (RSTs) was calibrated and validated. These source trains are used in the 5-F-BetaCath(TM) system (Novoste Corp.) for the treatment of endovascular diseases. The calibration factor of the OPTIDOS system was obtained empirically and is valid for Sr-90/Y-90 dose rate measurements at the specification point which is located at 2 mm distance from the source axis. A total of 187 OPTIDOS dose rate verifications of the 5-F-BetaCath(TM) system were performed in different hospitals. The histogram of the deviation between the manufacturer's dose rate specification and the dose rate measured using the OPTIDOS dosimetry system is Gaussian shaped with +/-3% relative width and a mean shift of about +2% with respect to the corresponding dose rate specification. Additionally, 128 OPTIDOS dose rate verifications of the new jacketed RST (3.5-F-BetaCath(TM), Novoste Corp.) were performed using the same calibration factor as derived for the 5-F-BetaCath(TM) system. Distribution of the deviation between the certified and the measured dose rate is nearly identical in comparison to the histogram of the 5-F-BetaCath(TM) system. The mean value of the deviations is shifted by - 1.5% with respect to the certified dose rate. In order to compare the results of the calibrated OPTIDOS dosimetry system with a standard measuring method, separate dose rate measurements were performed using electron accelerator calibrated radiochromic films in which calibration is traceable to PTB (Physikalisch Technische Bundesanstalt, Germany). Deviation between both the methods is less than 3.1%. These results confirm that the calibrated OPTIDOS dosimetry system can be considered suitable for quality assurance of both types of RST used in the BetaCath(TM) systems.