Personnel dosimetry & bioassay
Routine dosimetry for an Ac-225 program covers both external dose (from daughter gammas) and internal dose (from any uptake of the parent or daughters). The AMP and RSO together set the monitoring program based on expected workload, engineering controls, and the licensee's ALARA goals.
Three monitoring layers
External dosimetry
Whole-body badge for all restricted-area staff, exchanged on the licensee's standard cadence (monthly or quarterly). Ring badge for hot-lab compounding and dose-prep staff, placed per AMP guidance to capture realistic dose from daughter gammas.
Routine bioassay
Urine bioassay for staff who routinely handle open Ac-225, on a cadence set by the RSO (commonly monthly or per-batch for high-volume programs). Baseline samples collected for new staff before they begin work with the isotope.
Incident bioassay
Any suspected contamination event triggers prompt bioassay sampling. The window for detecting an inhalation or ingestion intake is narrow — sample early, not after paperwork. Document chain-of-custody and counting method per RSO procedure.
Regulatory anchors
Occupational dose limits
10 CFR §20.1201 sets the annual occupational TEDE limit (5 rem / 50 mSv) and organ/extremity limits. Internal and external dose are summed for the TEDE; an Ac-225 program's monitoring plan must support that summation.
Monitoring threshold
10 CFR §20.1502 requires monitoring for adults likely to receive >10% of the limit. For Ac-225 hot-lab staff, the default assumption should be that monitoring is required — opt-out only after a documented dose assessment.
Baseline bioassay results — captured before staff handle Ac-225, including at pre-employment — are worth having on file. Without a baseline to subtract, post-incident results can be ambiguous and harder to discuss with the regulator.
- 10 CFR §20.1201 — Occupational dose limits for adults.
- 10 CFR §20.1502 — Conditions requiring individual monitoring of external and internal occupational dose.
- NCRP Report No. 156 — Development of a Biokinetic Model for Radionuclide-Contaminated Wounds.