Dose calibrator

A dose calibrator is a shielded, re-entrant ionisation chamber used to measure the activity (in becquerels or curies) of a radiopharmaceutical dosage before it is administered to a patient. Under US Nuclear Regulatory Commission rules, licensees performing direct dosage measurements must possess and use such instrumentation (10 CFR 35.60, formerly the more prescriptive 35.50), and calibrate it in accordance with nationally recognised standards or the manufacturer's instructions.

Under the earlier, more detailed version of the rule (still widely followed as practice standard and reflected in NRC guidance such as NUREG-1556 Vol. 9), dose calibrators must be checked for constancy each day of use with a dedicated check source of at least 10 microcuries of radium-226 or 50 microcuries of any other photon-emitting radionuclide; tested for accuracy on installation and at least annually by assaying two sealed sources of different radionuclides, each within 5% of its manufacturer-stated activity; tested for linearity on installation and at least quarterly across the full range of clinical use down to 10 microcuries; and tested for geometry dependence on installation across the range of volumes and containers used clinically. A dose calibrator must be repaired or replaced if its accuracy or constancy error exceeds 10%, and records of every check and test must be retained (historically for three years, per 10 CFR 35.2060).

The dose calibrator is the instrument that closes the loop between the pharmacy's compounding or dispensing step and the patient: the final patient dose or ordered amount must be radioassayed in it before administration (except for certain unopened manufacturer unit-dose containers), and the measured activity is decay-corrected to the scheduled administration time to confirm it falls within the prescribed and regulatory tolerance. It sits physically in the hot lab alongside survey instruments and syringe/vial shields.