SU‐E‐I‐64: Weekly Exposure Contributions from Radioactive Patients in A Busy Comprehensive Imaging Center

Purpose: To investigate radiation exposure from radioactive patients to the surrounding workers in a busy comprehensive imaging center. Methods: Follow‐up of oncology patients often include nuclear medicine and diagnostic CT examinations. Many patients present themselves for CT imaging after they have been administered radioactivity. An Ion‐chamber survey meter (Victoreen 45 1p) was used to monitor the dynamic radiation environment in a CT facility. The survey meter was placed at a centrally located nurse station that was surrounded by 6 patient‐preparation rooms (at 2.5m away) and 5 CT scanners. The radiation environment was monitored for 5 days and correlated with the clinical schedule to estimate the radiation from radioactive patients. Typically 190 patients/day are scanned at this CT facility; ∼6% of which are radioactive (10 99mTcMDP and 1 18F‐FDG) patients). The typical doses for such procedures in our facility are 20mCi and 10mCi respectively. The air‐kerma rate was modeled based on Gamma Factor and ICRP‐53 biokinetic models for Tc‐99m‐labelled phosphates and 18F‐FDG. Results: In the absence of radioactive patients, the average radiation level was measured to be 0.05μSv/hr and independent of the CT duty‐cycle; thus validating the CT shielding design. The radiation level increased in the afternoon due to the presence of radioactive patients. The typical cummulative dose/day in the area was 1.3μSv, which is 3.25 times the background dose (0.4μSv). Our model predicts that 11 99mTcMDP patients or 418F‐FDG patients would contribute up to 5μSv/week (25% of the weekly limit) Conclusions: The presence of radioactive patients in the diagnostic CT facility may contribute non‐negligible radiation exposure to the employees in the surrounding the CT suite. If the exposure of a non‐ radiation worker can potentially exceed 25% of the annual effective dose limit, then the site operator should ensure that the annual exposure of the maximally exposed individual does not exceed 1 mSv.