PET Quality Control, Safety, and Regulations
What this domain tests
This domain covers the daily and periodic checks that keep PET/CT quantitative and safe, plus radiation protection and regulatory reporting. Expect practical numbers, frequency comparisons, and release criteria.
Core rules
- Dose calibrator QC: daily constancy (check against a long-lived source), plus periodic accuracy, linearity, and geometry. Record background and source activity; investigate deviations beyond institutional limits.
- PET/CT QC: daily detector/blank scans and uniformity checks; normalization and sensitivity per manufacturer; CT air/water calibration and warm-up. Annual physics calibration and accreditation surveys are separate from daily checks.
- Well counter and survey meter QC: daily background and efficiency checks; survey meters need annual calibration and battery checks.
- Radiation safety: use time, distance, and shielding. At 511 keV, lead is less effective than at lower energies; use appropriate shielding and maximize distance. Inverse square: doubling distance cuts exposure to one-quarter.
- Patient release under 10 CFR 35.75 requires instructions if the dose to others is likely to exceed 5 mSv (0.5 rem). Report medical events per 10 CFR 35.3045; keep receipt surveys, wipe tests, and dose records.
- ALARA: occupational limit 50 mSv/year; public 1 mSv/year.
Worked example
An unshielded source gives 40 µSv/h at 1 m. At 3 m, exposure = 40 × (1/3)² = 4.4 µSv/h. Moving from 1 m to 3 m is more effective than adding a thin lead shield at 511 keV.
Traps
Do not substitute daily constancy for annual calibration. Do not release a patient without checking the 5 mSv criterion and instructions. Do not treat 511 keV shielding like 140 keV technetium shielding; tenth-value layers are much thicker.