Effective Dose Reference: Common NM Procedures
Representative patient effective doses for counseling, ALARA justification, and modality comparison
Quick Answer
This is a representative table of patient effective doses (mSv) for common nuclear-medicine studies — for patient counseling, ALARA justification, and comparing modalities. Two anchors put them in context: natural background radiation ≈ 3 mSv/year, and a diagnostic chest CT ≈ 5–7 mSv. Values scale with administered activity (weight-based, lower in children) and, for hybrid studies, the CT component adds a variable dose (a low-dose attenuation-correction CT adds little; a diagnostic contrast CT adds several mSv). These are orientation figures — verify against the administered activity and local protocol.
⚠️ Representative adult values (radiopharmaceutical component unless noted). Actual dose depends on injected activity, patient size, and any CT. Sources: ICRP/SNMMI dose coefficients — confirm locally.
Diagnostic Studies (radiopharmaceutical component)
| Study | Agent (typical activity) | ~Effective dose (mSv) |
|---|---|---|
| Thyroid uptake/scan | I-123 (low activity) | ~1–2 |
| Renal dynamic | Tc-99m-MAG3 | ~1–2 |
| V/Q lung scan | Tc-99m-MAA + ventilation | ~2 |
| Hepatobiliary (HIDA) | Tc-99m-IDA | ~2–3 |
| Gastric emptying | Tc-99m-SC meal | ~0.3–0.4 |
| Bone scan | Tc-99m-MDP (~20–25 mCi) | ~4–6 |
| Brain FDG / DAT SPECT | F-18-FDG / I-123-ioflupane | ~5–7 / ~4 |
| FDG-PET (tracer only) | F-18-FDG (~10 mCi) | ~5–7 |
| PSMA / DOTATATE PET | Ga-68 / F-18 agents | ~3–8 |
| MPI — SPECT (Tc-99m) | sestamibi/tetrofosmin (1- or 2-day) | ~8–12 |
| MPI — SPECT (Tl-201) | thallium-201 | ~15–25 (higher) |
| MPI — PET (Rb-82) | rubidium-82 | ~3–4 (low) |
| MUGA | Tc-99m-RBC | ~6–8 |
| Ga-67 / labeled-WBC | Ga-67 citrate / In-111-WBC | ~10–15 / ~6–8 |
Context & Comparators
- Natural background: ~3 mSv/year (varies with altitude/geology).
- Chest radiograph: ~0.1 mSv; chest CT: ~5–7 mSv; abdomen/pelvis CT: ~8–10 mSv.
- Hybrid caveat: PET/CT and SPECT/CT add the CT dose — a low-dose AC CT adds ~1–4 mSv; a diagnostic (± contrast) CT adds more. Report total (tracer + CT) where it matters.
Therapy (context — not "effective dose")
Therapeutic activities deliver targeted absorbed doses (Gy) to tumor/organs, not a whole-body "effective dose" in the diagnostic sense — e.g., I-131 ablation ~30 mCi to ~150 mCi+, ¹⁷⁷Lu-PSMA/DOTATATE 7.4 GBq/cycle. These are governed by organ-at-risk dosimetry and patient-release rules, not the diagnostic dose framework.
How to Use This
- Counseling: frame diagnostic NM doses against background and CT — most studies are in the "few-mSv, comparable to months of background" range.
- Justification (ALARA): prefer the lowest activity consistent with a diagnostic study, non-ionizing alternatives where they answer the question, and weight-based pediatric activity (see pediatric dosimetry).
- Modality choice: e.g., Rb-82 PET MPI delivers less dose than Tl-201 SPECT — a real selection consideration.
Common Pitfalls
- Quoting a fixed dose without accounting for administered activity or the CT component.
- Comparing a tracer-only figure to a PET/CT total as if equivalent.
- Applying adult figures to children (weight-based, lower).
- Confusing therapeutic absorbed dose (Gy) with diagnostic effective dose (mSv).
Board Pearls
Most diagnostic NM studies deliver a few mSv — anchor counseling to background (~3 mSv/yr) and chest CT (~5–7 mSv). Typical figures: bone scan ~4–6, FDG-PET tracer ~5–7, V/Q ~2, HIDA ~2–3, MAG3 ~1–2, with Tc-99m MPI ~8–12 and Tl-201 higher (~15–25) but Rb-82 PET low (~3–4).
Hybrid studies add the CT dose — a low-dose AC CT adds a little, a diagnostic/contrast CT adds several mSv; report tracer + CT total when relevant. Values scale with administered activity and are lower (weight-based) in children.
Therapy is a different framework — targeted absorbed dose (Gy) to tumor/organs governed by organ-at-risk dosimetry and patient-release rules, not a diagnostic "effective dose." Modality selection can be dose-driven (Rb-82 PET < Tl-201 SPECT for perfusion).
Related Pages
- Physics: radiation biology & protection, pediatric dosimetry, dosimetry & theranostics; tool: effective-dose calculator.
Figure / Diagram Suggestions
- A dose-comparison bar (background yr / CXR / NM studies / CT) on one scale.
- A tracer + CT stacked-dose illustration for hybrid imaging.
Self-Check
Q1. Roughly what effective dose does a Tc-99m bone scan deliver, and how does it compare to annual background?
Answer: ~4–6 mSv — roughly one to two years of natural background (~3 mSv/yr).
Q2. Why can two "FDG-PET" doses differ substantially?
Answer: The CT component — a low-dose attenuation-correction CT adds little, a diagnostic/contrast CT adds several mSv on top of the ~5–7 mSv tracer dose.
Q3. Which myocardial-perfusion approach delivers the least dose: Tl-201 SPECT, Tc-99m SPECT, or Rb-82 PET?
Answer: Rb-82 PET (~3–4 mSv) — lower than Tc-99m SPECT (~8–12) and much lower than Tl-201 (~15–25).
Q4. Why is a therapeutic I-131 activity not described as an "effective dose"?
Answer: Therapy delivers a targeted absorbed dose (Gy) to tumor/organs governed by organ-at-risk dosimetry and patient-release rules — a different framework from the diagnostic whole-body effective dose (mSv).
Evidence & sources
https://nuc.med/effective-dose-reference/ Report an issue