Leakage radiation and workplace monitoring of a cobalt-60 teletherapy facility in South-West Nigeria: Is the dose significant?

Abstract

BACKGROUND: Cobalt-60 (Co-60) teletherapy machines are still in use in most developing countries because of their minimal power requirements, reduced operational cost, and since the source does not vary in energy, the amount of quality assurance required to ensure “good beam” is dramatically reduced. Although as the machine wear, the chances of leakage radiation increase. AIMS AND OBJECTIVES: The aim of this study was to determine if leakage radiation at 5 cm and 1 m from the Co-60 teletherapy source head is within the acceptable tolerance limit set by the International Electro-technical Commission (IEC) and to determine if controlled and supervised areas within working hours were within the Institute of Physics and Engineering in Medicine (IPEM) limit. MATERIALS AND METHODS: The machine used was a Theratron® Phoenix Cobalt 60 Teletherapy machine. A RadEye™ B20-ER Multi-Purpose Survey Meter was used to measure mean time-average dose rate (TADR) at various points in the controlled and supervised areas. Instantaneous dose rate (IDR) for leakage radiation was measured at 5 cm from the source head using the same Survey Meter and a measuring tape. In addition, measurement was made at 1 m from the normal treatment distance in patient and nonpatient planes. RESULTS: The mean TADR at beam OFF position in the controlled area at four different areas was 2.15 ± 0.48 μSv/h, which was <7.5 μSv/h IPEM limit and mean TADR in the supervised area at six different areas was 1.70 ± 0.45 μSv/h, which was also <2.5 μSv/h IPEM limit. The percentage IDR leakage radiation at beam OFF position at 5 cm and 1 m was within 200 μSv/h and 20 μSv/h IEC tolerance limit, respectively. Percentage leakage radiation at beam ON in patient plane was below the maximum and average IEC tolerance limit and nonpatient planes at 1 m was below 0.5% IEC limit. CONCLUSION: Supervised and controlled areas were within the acceptable range. Leakage radiation was within the tolerance limit.