Interactive dosimetry learning tool
MIRD concepts · made visual
How long activity stays changes how much dose lands.
Move the effective half-life slider and watch the time-activity curve, integrated activity, and absorbed dose change together.
The idea:
a longer effective half-life creates a larger area under the activity-versus-time curve. In this simplified MIRD example, that means more time-integrated activity and more absorbed dose.
Activity over time
The shaded area represents time-integrated activity (Ã).
Reference
New scenario
At one effective half-life, activity has fallen to 50% of A₀.
Time shown in hours
Reference dose
173 mGy
à = 3,462 MBq·h
New scenario dose
346 mGy
à = 6,925 MBq·h
Change from reference
+100%
Dose is higher
Longer retention increases dose
The effective half-life doubled, so time-integrated activity and absorbed dose doubled in this simplified model.
2.00×
Absorbed-dose comparison
The MIRD chain in three steps
Activity curve
A(t) decreases over time
→
Integrate the curve
Area = Ã
→
Apply S
D = Ã × S
In a full MIRD calculation, contributions from multiple source regions can be summed for each target region.
Quick challenge
If effective half-life doubles while A₀ and S remain unchanged, what happens to absorbed dose in this model?
Choose an answer to reveal the relationship.
ARC Workshop #2 · Novel Theranostics
Go beyond the slider: see where theranostics is heading next.
Friday, June 26, 2026 · 8:00 AM–5:00 PM · Fralin Biomedical Research Institute at VTC · Roanoke, Virginia · Free registration · 6.25 CE hours
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