DECOMMISSIONING OF TELETHERAPY MACHINE AND TRANSPORT OF DECAYED TELETHERAPY SOURCE

Abstract

Radioactive Cobalt-60 teletherapy machines find a prominent place in radiation therapy departments in India. The first teletherapy cobalt machine in SMS hospital (Picker Advance Tele Cobalt (ATC) C/9) was installed in 1995. The initial activity of the cobalt source was 333 TBq (9000 Ci).In March 2019, the source output became lesser than 50 cGy/hr at normal treatment distance (NTD) of 80cm which is clinically not acceptable for patient treatment because of increase in treatment time. The decommissioning of the machine was considered due to ageing of machine and vendor was not providing services anymore. This present study describes radiation safety aspect of the planning of decommissioning of teletherapy machine and transport of the decayed Cobalt-60 source for disposal and personnel dose measurements during the procedure. Decommissioning of the cobalt machine began with preparation of a plan and its submission for approval by competent national authority. Radiation survey of the source head was performed before the source transfer operation by AERB certified decommissioning engineers. Then decayed source was unloaded in shielded container (flask Sl No 112) and was kept in another outer container (type B (U) package). It transported for disposal to BRIT, Kota on receipt of transport permission fromAERB.A radiation survey was done in a matrix format of the all sides of this package.To measure the personnel doses, pocket dosimeter, TLD badge and OSLDs were used. The maximum dose received by the engineers was .03mSv. Maximum radiation level at 1 m from the external surface of the package was found 0.83mR/hr. The development of the new concepts and practices in the field of the decommissioning includes the preparation and approval of a decommissioning plan, the actual decommissioning operations as well the safe management of the waste arising from the decommissioning process. Such plans need to be developed for each facility with radiation sources.