On the actual state of industrial quality assurance procedures with regard to (106)Ru ophthalmic plaques.

Abstract

In radiotherapy of intraocular tumors, e. g., in the case of malign choroid melanomas, episcleral brachytherapy with (106)Ru ophthalmic plaques has proven to be successful. In a study, the authors reported on the discovery of the following shortcomings in industrial quality assurance, which are relevant to therapy, during the course of an internal clinical acceptance test of (106)Ru ophthalmic plaques, manufactured by the company Bebig from Berlin, Germany. This consisted of inconsistent dose rate specifications in the manufacturer's certificate, covering a range of 111% and with the risk of leakage of the plaques. Bebig was called upon to adapt state-of-the-art production methods with regard to (106)Ru ophthalmic plaques. In the meantime, Bebig has modernized production of (106)Ru ophthalmic plaques and adopted all the quality assurance procedures proposed by the authors. Moreover, the requested traceability of the calibration of activity and dose rate of the (106)Ru ophthalmic plaques to standards of the federal authorities in charge of measurement procedures has been implemented. In the year 2002, Bebig updated, among other things, the ASMW (GDR) calibration of the dose rate of the (106)Ru ophthalmic plaques from the years 1987-1989 by a calibration of the NIST (USA). The current NIST calibration, together with the new equipment for the measurement of the depth dose curves, led to the consequence that the new NIST 2001 dose rate values show, in the mean, a deviation of 0.75 times (plaque type CCC) up to 2.06 times (plaque types CCX, CCY, and CCZ) compared to the dose rate values that had been indicated so far in Bebig's certificate, based on the ASMW 1987 calibration. For the 95% confidence interval, Bebig estimated the measurement uncertainty to be +/- 25%. If one takes into consideration the minimal and maximal values in such 95% confidence intervals, it follows that the new NIST 2001 dose rate values deviate between 0.56 times (plaque type CCC) and 2.58 times (plaque types CCX, CCY, and CCZ) from the Bebig certificate (ASMW calibration 1987). As regards leakage, no objections arose in the case of the (106)Ru ophthalmic plaques produced according to the new quality standards. Legislation has to make sure that the use of radioactive material on humans be, among other things, permitted as a matter of principle only, if the dose rate calibration can be traced to standards of a federal authority of measurement procedures. Furthermore, special leakage tests for radiation sources which come into direct contact with body fluids should be established. A historical retrospect reveals that the greatest changes have taken place in the indication of the dose rates of (125)I sources. Since the beginning of the use of (125)I sources in brachytherapy in the late 1960s, the dose rate indications, so far, have had to be reduced in small steps over a period of about 35 years by nearly a factor of 2. As regards the (106)Ru ophthalmic plaques, the NIST 2001 calibration has resulted in a comparable reduction of the dose rate indications of up to a factor of 2 within the period of about several months. Thus, in the previous history of radiotherapy this case must be regarded as unique, because for the first time ever, an urgently needed recalibration has been protracted for such an unduly long period of time.