Radiopharmacist's Notes · EVial Sealed Sources

Eight steps between morning warm-up and signed-off constancy.

A daily constancy reading is the first defence against dispensing wrong activity. This post walks the eight-step SOP, the trending log the physicist relies on, and the AERB inventory + return cycle that surrounds the sealed source over its multi-year service life.

The eight-step SOP

From morning warm-up to signed record

1

Before first dose dispensed

Power on dose calibrator, allow ≥ 30 min warm-up before the first constancy measurement.

Cold electronics drift; the AERB / AAPM guidance assumes a stable thermal state.
2

Background

Empty-well background reading, recorded in MBq, with isotope set to the source under test.

Background subtraction is automatic on modern calibrators but the raw reading goes into the log.
3

Insert EVial reference

Insert the EVial sealed reference source into the calibrator well in the same orientation every day.

Orientation matters for chamber response symmetry; mark the source with a top arrow.
4

Read activity

Record the measured activity at the time of reading.

Dose calibrator displays in MBq or mCi — keep the unit consistent across the log.
5

Decay-correct expected

Calculate the expected activity from the certificate using the elapsed time and isotope half-life.

Most QA software computes this; if not, A_expected = A₀ × exp(-ln 2 × t / T½).
6

Compute % difference

Δ = (A_measured − A_expected) / A_expected × 100 %. Record on the constancy trend log.

Sign matters — a consistent positive or negative drift is a trend signal even if within tolerance.
7

Compare against threshold

Δ within ± 5 %: PASS, dispense. Δ between ± 5 % and ± 10 %: investigate. Δ > ± 10 %: HOLD, escalate to physicist.

AERB tolerance for daily constancy. ± 10 % is the action threshold per AAPM TG-181.
8

Sign and store

Sign the constancy record. Replace the source in the storage cabinet behind the dispensing isolator shielding.

AERB inspection looks for signed, dated daily records — not just stored printout receipts.

Source: AAPM TG-181 PET / Nuclear Medicine QA; AERB Safety Code for Nuclear Medicine Facility.

Trending

What the physicist needs from the constancy log

Plot Δ % vs date on a control chart with ± 5 % warning lines and ± 10 % action lines. Send a screenshot to the physicist monthly.
A single point > ± 5 % is not action — three consecutive points on the same side, or one > ± 10 %, is.
Trend logs survive five years per AERB inventory requirements. Store the source-certificate PDF alongside the trend log so the certificate is always at hand for inspection.
When the source approaches end of useful life (annual replacement for Co-57; multi-year for Cs-137 / Ba-133 / Co-60), the trending log shows declining signal-to-background ratio — the trigger to order a replacement is signal-to-background, not headline activity.

Inventory + AERB cycle

The paperwork around the source, not just the source

The EVial sealed source is on the AERB facility-inventory list. Annual AERB returns include the source serial number, isotope, activity-at-calibration and current decay-corrected activity.
A wipe test (smear test) is required at the cadence the AERB licence specifies (typically annual for sealed sources). The radiopharmacy holds the wipe-test certificate alongside the constancy log.
End-of-life return flows through the Saxsons Source Return Service — Saxsons supplies the AERB transport documentation, the decay-store coordination and the final disposal certificate. The radiopharmacy does not need to find a separate disposal vendor at end of life.

Source: AERB Atomic Energy (Radiation Protection) Rules 2004; Saxsons Source Return Service product page.