ALARA for an alpha program
ALARA — As Low As Reasonably Achievable — is required of every medical-use licensee under 10 CFR §20.1101. For an Ac-225 program, the classical ALARA levers (time, distance, shielding) still apply to external dose from daughter gammas, but the dominant ALARA conversation is internal dose: keeping activity inside containment and off of people.
The three classical levers — re-tuned for alpha
Time
Minimize hands-on time during dose draw, transfer, and administration. The Bi-213 gamma builds in within minutes of preparation; rehearsing the workflow on cold runs is the single most effective time-based ALARA control.
Distance
Use tongs, syringe shields, and remote-handling tools for every step where they fit. Plan the hot-lab footprint so that compounding, dose calibration, and packaging happen at arm's-length-plus from the operator's body.
Shielding
Shielding for Ac-225 is shielding for the daughter chain. L-blocks, syringe shields, vial pigs, and transport containers should be designed and verified against Bi-213's 440 keV photon, not the parent alpha.
Two ALARA levers specific to alpha
Containment
Engineering controls — HEPA-ventilated hoods, negative-pressure compounding, dedicated tools, drip trays — are the alpha equivalent of shielding for gamma. Most internal-dose risk is eliminated by never letting activity become airborne or mobile in the first place.
Procedural discipline
Double-glove changes after each handling step, dedicated PPE that doesn't leave the restricted area, and a 'no-bare-hands, no-uncovered-surface' rule for the hot lab. Procedural drift is the most common root cause on alpha contamination events.
Setting internal action levels for bioassay results well below the regulatory limit can help surface procedural drift before it becomes a reportable event. A modest urine-bioassay threshold reviewed monthly by the RSO tends to catch issues early.
- 10 CFR §20.1101 — Radiation Protection Programs (ALARA).
- NCRP Report No. 168 — Radiation Dose Management for Fluoroscopically-Guided Interventional Medical Procedures (ALARA principles).