Radiation Safety Issues in PET/CT

Welcome to the 12th webinar in the Lunch, Learn, and Dance Wellness series, focusing on radiation safety issues in PET/CT. The session will cover an overview of ionizing radiation, Canadian regulations, PET/CT procedures, radiation dose, and protection considerations. Questions can be submitted via the Q&A section, and answers, along with slides and a video recording, will be posted on the website. An attendance confirmation email will be sent, detailing topics and duration for professional associations. Closed captioning is available.

Radiation is a form of energy that can be transferred to matter, either beneficially or harmfully. Ionizing radiation, energetic enough to remove electrons from atoms, comes from radioactive atoms (natural and man-made) and man-made devices like X-ray units. The webinar focuses on beta, gamma, and X-ray radiation relevant to PET/CT. Beta particles are charged particles from atomic nuclei, including positrons (positive) and electrons (negative). Gamma rays are emitted from radioactive nuclei after decay, and X-rays are produced when high-speed electrons are slowed or change direction. Shielding for radiation varies: plastics or aluminum for beta particles, and high-density materials for gamma and X-rays, recognizing that beta emitters can also emit gamma radiation, necessitating a multi-layered shielding approach.

Radiation regulation in Canada is divided between provincial/territorial and federal jurisdictions. X-ray equipment, low-energy particle accelerators, and non-ionizing radiation sources are typically provincially regulated. Naturally Occurring Radioactive Material (NORM) also falls under provincial/territorial control, except for transport, import, and export, which are federal. The federal government, through the Canadian Nuclear Safety Commission (CNSC), regulates all aspects of nuclear energy, including PET locations and related equipment like calibrators and source holders. The CNSC, an independent administrative tribunal with over 800 employees, reports to Parliament and ensures the safe use of nuclear energy and materials, implements international commitments, and provides public information through transparent decision-making.

PET/CT is highly regulated due to its complex nature, combining Positron Emission Tomography (PET) and Computed Tomography (CT). PET provides functional information using short-lived radiopharmaceutical tracers, produced nearby due to their short half-lives, to identify 'hot spots' of biological activity. CT offers detailed anatomical information but cannot distinguish between active and benign diseases. The combination, PET/CT, merges functional and anatomical data for higher diagnostic accuracy. The procedure involves a cyclotron (a Class II nuclear device for producing radioisotope tracers), unsealed radiopharmaceuticals, and a high-dose CT scanner that performs multiple scans rapidly. Cyclotrons, though older technology, are still used for short-lived medical isotope production and are federally regulated due to their energy output.

Radiation protection in PET/CT requires understanding health effects and dose. There are two types: stochastic effects (increased risk of an outcome, like cancer, with higher exposure) and deterministic effects (occur above a threshold dose, like cataracts, blood changes, or nausea). Background radiation exposure for Canadians is typically 2-4 millisieverts per year. While PET/CT delivers a considerable dose compared to background, it's generally far below the threshold for deterministic effects, excluding cataracts. The procedure is typically used for serious conditions where the diagnostic benefit outweighs the radiation risk, especially for older patients. The ALARA (As Low As Reasonably Achievable) principle guides dose reduction. The International Commission on Radiological Protection (ICRP) recommends a lower dose limit for the lens of the eye (20 millisieverts/year, averaged over five years, with no single year exceeding 50 millisieverts), prompting CNSC to align its limits. Staff working in PET/CT must be knowledgeable in both nuclear medicine and radiology for effective radiation protection, considering the open nuclear sources and high-dose X-ray equipment involved.

CNSC licensed facilities must have a Radiation Protection Program implemented by a Radiation Safety Officer, emphasizing the ALARA principle. Procedures like minimizing time near sources, maximizing distance, and using appropriate shielding are crucial. Engineering and administrative controls, along with standard operating and emergency procedures, are required. Dosimetry is used for designated staff to track doses. Staff need proper training, and regular inspections ensure compliance. Special consideration is given to pregnant workers and children due to their increased sensitivity to radiation. The CNSC provides extensive resources, including technical information, guidance documents, and regulatory documents. The International Society of Radiology (ISR) and its Quality and Safety Alliance (QSA) promote quality and safety in diagnostic medical imaging, advocating for initiatives like the Bonn Call for Action. This call encourages coordinated efforts to address radiation protection in medicine, leading to the development of 'safe imaging' organizations worldwide, such as Canada Safe Imaging (CSI). The International Atomic Energy Agency (IAEA) also offers a wide range of relevant resources, including safety standards, guidance on clinical implementation, quality management, and emergency preparedness for PET/CT.