Room: ePoster Forums
Purpose: Replacement of medical linear accelerators necessitates the decommissioning and disposal of used systems and ancillary components, e.g., a tertiary micro multi-leaf collimator (mMLC). Neutron-generating interactions may occur within the head of the linear accelerator, resulting in the activation of device components, complicating disposal. The degree and byproducts of activation varies according to material constituents, and resultant unstable radioisotope half-lives may range from minutes to years. As such, care must be taken to satisfy federal (10 CFR 20) or Agreement State radiation protection requirements before disposal. Presented is a method that was used to evaluate a mMLC upon decommissioning to ensure regulatory compliance.
Methods: Historical patterns of device use (e.g., nominal energy and technique) and vendor-provided data describing mMLC components were reviewed to determine materials prone to activation. Measurements were performed to access compliance with disposal guidelines: (1) a micro-rem tissue equivalent survey meter to assess gamma dose-rate, (2) a Geiger-Muller pancake-type detector to evaluate overall alpha, beta and gamma radioactivity surface contamination, (3) a NaI(Tl) scintillator detector to determine low energy gamma contamination, and (4) a portable, solid-state gamma-ray spectrometer (10 keV to 2 MeV window) to identify any residual radionuclides. Finally, wipe tests of individual mMLC components were evaluated for removable contamination (alpha, beta, gamma) using a low activity liquid scintillation analyzer (0 to 2000 keV window).
Results: No exposure or contamination above background levels was observed via direct measurement, in-field spectroscopy survey detected no radionuclides, and wipe test results detected no removable contamination.
Conclusion: A comprehensive method to measure exposure, surface and removable contamination was used to confirm a mMLC was non-activated and safe for disposal. A summary report was filed with the facilityâ€™s Radiation Safety Officer documenting compliance with the State criteria.