[Therapy relevant weak sites in industrial quality assurance of 106Ru eye plaques]

Beta emitting 106Ru applicators manufactured by Bebig GmbH (Berlin, Germany) are widely used to treat intraocular tumors. The applicators are fixed to the bulbus and removed after several days. The following therapy relevant defects have been detected by an internal clinical acceptance test: risk of leakage and inconsistent dose-rate specifications by the manufacturer. In the meantime, components of the internal clinical acceptance test have been adopted successfully by the manufacturer of the 106Ru ophthalmic plaques.

106Ru ophthalmic plaques were tested with the following internal clinical acceptance tests: visual inspection, surface contamination, leakage, and dose-rate verification. The surface contamination test consists of a wet wipe test at moderate pressure. For the leakage test of the 106Ru ophthalmic plaques a clinically relevant scenario was developed in which the contact of the applicator with human tissue is simulated. In the course of it the applicator is inserted into Ringer's solution for several days. The certified energy dose-rate statements of the manufacturer are examined with a 1 mm3 plastic scintillator for consistency.

During the internal clinically acceptance tests of 106Ru ophthalmic plaques of different size the following results were obtained: The leakage test was performed with seven applicators and yielded measurements for two 106Ru ophthalmic plaques that were significantly higher than those of a dummy sample. The highest value of a wipe test was 57 Bq (Figure 1). The highest value in Ringer's solution was 520 Bq (Figure 2). During the dosimetry consistency checks of the certified dose-rate specifications for 14 applicators, six applicators were in good agreement with a variation coefficient of 2.6%. For the other eight applicators the deviations were between -37% and +74% (Figure 3), i.e. the range of the unaccepted applicators amounts to 111%. The results were representatively verified through external assessment.

Grave therapy relevant shortcomings of the industrial quality assurance of ophthalmic plaques were uncovered by experimental cross-checks. It is necessary that every radioactive device is internally examined before its use. The internal clinical acceptance test of the 106Ru ophthalmic plaques can easily be adopted by other hospitals.