🏠 I-131 Post-Therapy Contact / Release Time (Rough)
Rough time for I-131 activity to fall below a selectable threshold (e.g. historical 33 mCi outpatient context). Educational only — not a release authority.
Not a release tool.
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When to use
Teaching contact-restriction magnitude. Written institutional/RSO/national instructions always override.
How it works
t = ln(A0/A_thr)/(ln2/T½); default physical T½=8.02 d; optional Teff.
Key points
- Not a release tool.
- Thresholds are jurisdiction-specific.
- Physical T½ is conservative.
References
- NRC / SNMMI patient-release guidance concepts (activity/dose-rate criteria; jurisdiction-specific)
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Administered/residual activity | 100 |
|---|---|
| Unit | mCi |
| Activity threshold | 33 mCi (1.22 GBq · US outpatient historical) |
| Effective half-life Teff (optional) | 2.5 d |
| Dose-rate limit (optional) | 50 µSv/h |
→Rough estimate (physical T½)12.83 d
- Activity：100 mCi / 3700 MBq
- Threshold：33 mCi (1221 MBq)
- Days to threshold (physical T½)：12.83 d
| Administered/residual activity | 100 |
|---|---|
| Unit | MBq |
| Activity threshold | 5 mCi |
| Effective half-life Teff (optional) | 2.5 d |
| Dose-rate limit (optional) | 50 µSv/h |
→Rough estimate (physical T½)Already below selected threshold
- Activity：2.703 mCi / 100 MBq
- Threshold：5 mCi (185 MBq)
- Days to threshold (physical T½)：Already below threshold
Frequently asked questions
- What is I-131 Post-Therapy Contact / Release Time (Rough)?
- Rough time for I-131 activity to fall below a selectable threshold (e.g. historical 33 mCi outpatient context). Educational only — not a release authority.
- How is I-131 Post-Therapy Contact / Release Time (Rough) calculated? What is the core formula?
- t = ln(A0/A_thr)/(ln2/T½); default physical T½=8.02 d; optional Teff.
- When is I-131 Post-Therapy Contact / Release Time (Rough) used?
- Teaching contact-restriction magnitude. Written institutional/RSO/national instructions always override.
- What are the key clinical points for I-131 Post-Therapy Contact / Release Time (Rough)?
- Not a release tool. Thresholds are jurisdiction-specific. Physical T½ is conservative.
- What are the limits and cautions when using I-131 Post-Therapy Contact / Release Time (Rough)?
- For licensed clinicians and clinical researchers. Interpret results with history, investigations and local protocols; not a diagnosis or prescription, and not a substitute for multidisciplinary decision-making or local guidelines.
- How is I-131 Post-Therapy Contact / Release Time (Rough) calculated in practice? Can you show a worked example?
- Inputs: Administered/residual activity 100, Unit mCi, Activity threshold 33 mCi (1.22 GBq · US outpatient historical), Effective half-life Teff (optional) 2.5 d, Dose-rate limit (optional) 50 µSv/h → Result: Rough estimate (physical T½) 12.83 d（Activity: 100 mCi / 3700 MBq, Threshold: 33 mCi (1221 MBq), Days to threshold (physical T½): 12.83 d） Inputs: Administered/residual activity 100, Unit MBq, Activity threshold 5 mCi, Effective half-life Teff (optional) 2.5 d, Dose-rate limit (optional) 50 µSv/h → Result: Rough estimate (physical T½) Already below selected threshold（Activity: 2.703 mCi / 100 MBq, Threshold: 5 mCi (185 MBq), Days to threshold (physical T½): Already below threshold）
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