Knowledge Hub · EVial Sealed Sources
A constancy reading only confirms a dose calibrator if the source geometry on the reference matches the geometry of the clinical vial being dispensed. The EVial format is the standard polyethylene-vial geometry used across diagnostic radiopharmaceuticals — and the sealed epoxy matrix inside it survives years of routine QA without settling, leakage or geometry drift. This page walks why those two facts matter and what NIST traceability buys at AERB inspection.
Why this matters
Geometry-matched reference
A dose calibrator's reading depends on isotope and on container geometry. The EVial polyethylene format is the standard reference geometry for daily constancy testing because it matches the external form factor of a clinical radiopharmaceutical vial. Reading the EVial source confirms the dose calibrator response in the same geometry used to dispense patient doses — not a different shielded reference whose calibration factor lives in a different table.
Based on: AAPM TG-181 Quality Assurance for PET / Nuclear Medicine; AERB Safety Code for Nuclear Medicine Facility.
Read source ↗Sealed epoxy matrix
The radionuclide is uniformly dispersed in an epoxy resin sealed inside the polyethylene vial. There is no liquid to leak, no precipitate to settle, no concentration gradient to develop over years of use. The geometry the calibrator reads on day one is the same geometry it reads in year three — the dominant reason an EVial source can serve a multi-year QA programme without re-qualification.
Based on: Manufacturer sealed-source construction dossier; ISO 2919 sealed-source classification.
Read source ↗NIST traceability
Each EVial source ships with a Certificate of Analysis stating the activity, calibration date and NIST traceability statement. NIST traceability means the supplier compared the source against a NIST primary standard; the chain is documented; the AERB inspection officer can verify it. Constancy and accuracy QA records anchored on a NIST-traceable source carry inspection weight that an uncertified in-house cross-reference does not.
Based on: NIST Special Publication 250 — calibration services for radioactivity; AAPM TG-181.
Read source ↗Isotope across the clinical span
EVial sources are available across Co-57 (122 keV), Ba-133 (81 keV), Cs-137 (662 keV), Co-60 (1,173 / 1,332 keV) and other long-lived radionuclides. The choice maps onto the clinical workflow: Co-57 sits at the Tc-99m energy window for daily constancy in a SPECT-dispensing department; Cs-137 spans the full activity range for linearity testing; Ba-133 anchors low-energy verification when adding I-123 or other low-energy isotopes.
Based on: AERB Safety Code for Nuclear Medicine Facility; AAPM TG-181 isotope-table guidance.
Read source ↗AERB sealed-source dossier
An EVial sealed source is regulated under AERB Atomic Energy (Radiation Protection) Rules 2004. Saxsons supplies the AERB sealed-source import licence, the facility-registration paperwork the radiation safety officer files, and the consignment shipping manifest. The hospital adds the source to its in-service inventory; the end-of-life return flows through the Saxsons Source Return Service.
Based on: AERB Atomic Energy (Radiation Protection) Rules 2004.
Read source ↗Multi-year service life
Cs-137 (T½ 30.1 y), Ba-133 (T½ 10.5 y) and Co-60 (T½ 5.27 y) carry useful activity through multiple AERB inspection cycles. The cost per QA measurement drops over the service life; the constancy record stays anchored on a single source set rather than a churn of replaced references. Co-57 (T½ 272 d) replaces annually and pairs with the Co-57 flood-source replacement cycle.
Based on: AAPM TG-181; IAEA TECDOC reference-source guidance.
Read source ↗The AAPM, AERB, NIST and ISO documents that frame sealed-source reference QA in nuclear medicine.
AAPM task-group framing for dose-calibrator constancy, accuracy and geometry-specific calibration factors.
Indian regulatory framework for sealed-source import, handling, decay-store and disposal.
NIST primary standards laboratory framing the traceability chain on the source certificate.
International sealed-source classification standard governing leak, temperature, pressure and impact ratings.