Leakage test methodology development in iodine-125 seeds production

Abstract

Brachytherapy using iodine-125 seeds has been used in prostate cancer treatment. In the quality control routine during seed production, leakage tests are taken to detect any leakage of radioactive material from inside the titanium shield, avoiding patient contamination. Leakage tests are carried out according to the International Standard Organization e Radiation protection e sealed radioactive sources e ISO 9978. This standard recommends different methods of essay applied to radioactive seeds. The aims of this work were the study of the different leakage test methods applied to radioactive seeds recommended by the ISO 9978 and the choice of the appropriate method to be used in the seeds production. The authors evaluated five different immersion methods to detect leakage, following the standard guidance, and in some case exceeding its requirement. One hundred iodine-125 seeds were intentionally cuted, causing the release of its content. Each immersion method was applied to twenty seeds. After the immersion period, the resulting liquid activity was measured. The activity values measured in the immersion liquid indicated best results with distilled water as immersion liquid and with the application of ultrasound to the bath. The temperature of the bath ranged from 20 C to 70 C and the immersion time ranged from 30 min to 24 h. In this experiment, the use of scintillator liquid as immersion liquid was not effective to detect the leakage. The results allow the authors to choose the best methods to be applied in the production routine, to detect leakage in the seeds. The choice of the method will also depend on the production rhythm for schedule. In a moderate production rate, the test at 20 C and 24 h immersion may be used. In a fast production rhythm, the shortest test 50 C or 70 C should be used.