Beta radiation exposure of medical staff and implications for extremity dose monitoring

Sealed and unsealed beta radiation sources come into use to a greater extent in radiation therapy, e.g. for treating inflammatory joint diseases by radiosynoviorthesis (RSO), by injecting (90)Y, (186)Re or (169)Er-solutions. Sealed (90)Sr/(90)Y and (32)P-sources or (188)Re-liquid-filled balloon catheter are applied in vascular brachytherapy. Recently, (90)Y-labelled antibodies are being successfully used in radioimmunotherapy (RIT) of malign lymphoma. Such practices require handling of high activities at small distances to the skin. Thus, the medical staff may be exposed to high beta doses. Investigations of the extremity exposure were performed at several workplaces, in particular during RSO treatments. The local skin dose (LSD), Hp(0,07), was measured with thin-layer TLD (LiF:Mg,P,Cu) fixed to the fingers (TLD-tapes). The findings indicate that the exposure of the staff can exceed the annual dose limit of 500 mSv when working at low protection standard. Routine monitoring of the extremity exposures with ring dosemeters appropriate to beta radiation and provided by the approved German dosimetry services was found to be needed. But even monitoring with these official 'beta-dosemeters' does mostly not give suitable results to demonstrate compliance with the dose limit. A study was conducted at RSO-workplaces in order reveal a correlation between doses measured with ring dosemeters and the maximum LSD obtained from the TLD-tapes. The results are discussed and conclusions for routine monitoring are drawn.