Radiopharmaceutical Decay Calculator

Activity at injection, net administered activity after the syringe residual, and when a dose reaches its prescribed activity.

Physical decay only, using A = A0 × 0.5t / T½. Half-lives are the DDEP recommended values.

Input Parameters

Activity unit

Dose calibrator assay

Injection

Residual in syringe (optional)

Prescribed activity (optional)

Shows when the dose reaches this activity, and how much to assay for it at the injection time.

Results

Time from assay to injection --
Remaining at injection --
Activity at injection --
Residual, decay-corrected to injection --
Net administered activity --
Dose reaches prescribed activity --
Assay needed for prescribed activity at injection --
A = A₀ × 0.5^(t / T½)

Summary

Choose an isotope and enter the assayed activity with its date and time.

Activity over time

The curve appears once the assayed activity and its time are entered.

How it is calculated

  • Decay: A(t) = A0 × 0.5t / T½ = A0 × e−λt, with λ = ln 2 / T½.
  • Net administered activity: activity at injection minus the syringe residual, with the residual decay-corrected back to the injection time.
  • Time to reach the prescribed activity: T½ × log2(Aassay / Aprescribed) after the assay.
  • Assay needed: Aprescribed × 2t / T½, where t is the time from assay to injection.
  • Units: 1 mCi = 37 MBq; 1 GBq = 1,000 MBq.
  • Limits: physical decay only; no biological clearance. Accuracy still depends on the dose calibrator setting and syringe geometry.

Half-lives used

IsotopeHalf-lifeIn minutes

References

  • Laboratoire National Henri Becquerel. Decay Data Evaluation Project (DDEP) recommended data. lnhb.fr (checked October 2026).

For education and as a quick check. Follow your radiopharmacy's dose records and institutional procedures for patient doses.