Serial Dosimetry Calculator

Patient-specific absorbed dose calculation from serial SPECT/CT measurements using EANM/SNMMI 2025 methodology.

New in v2.0: Patient-specific organ masses, bi-exponential fitting with model selection (AIC), uncertainty propagation, and updated EANM/SNMMI 2025 dose limits.

Treatment & Measurements

Treatment Parameters

Administered Activity (GBq) Standard dose: 7.4 GBq per cycle

Target Organ

Patient-Specific Organ Mass

Enter CT-derived organ mass for accurate S-value adjustment. Leave blank for standard phantom values.

Serial Measurements

Enter organ-specific activity from post-treatment SPECT/CT at different time points. Minimum 3 measurements, 3-4 recommended for optimal bi-exponential fitting.

Optimal Time Points (EANM/SNMMI):
• 4h: Early distribution, fast component
• 24h: Peak uptake, biological clearance
• 72-96h: Effective half-life determination
• 168h (7d): Long-term retention

Measurement 1 (4h)

Time (hours)

Activity (% ID or MBq)

Measurement 2 (24h)

Time (hours)

Activity (% ID or MBq)

Activity Unit % ID automatically converts using administered activity

Intelligent Model Selection

The calculator automatically selects the best fitting model using Akaike Information Criterion (AIC): Mono-exponential for simple kinetics, Bi-exponential for tumors and complex clearance. R² and uncertainty are reported for quality assessment.

Calculation Methodology

Step 1: Time-Activity Curve Fitting

• Model Selection: Akaike Information Criterion (AIC) compares mono- vs bi-exponential fits

• Mono-exponential: A(t) = A₀ × e^-λt(simple clearance)

• Bi-exponential: A(t) = A_fast × e^-αt+ A_slow × e^-βt(tumors, complex kinetics)

• Quality Metrics: R² goodness-of-fit, residual analysis

Step 2: Cumulative Activity (A~)

• Mono-exponential: A~ = A₀ / λ (MBq·h)

• Bi-exponential: A~ = A_fast/α + A_slow/β (MBq·h)

• Conversion: A~ (MBq·h) → A~ (MBq·s) × 3600

Step 3: Patient-Specific S-values

• Source: MIRD Pamphlet 21 (loaded from JSON)

• Mass Adjustment: S_patient= S_phantom× (M_phantom/ M_patient)

• Units: mGy/(MBq·s)

Step 4: Absorbed Dose Calculation

• MIRD Formula: D = A~ × S (Gy)

• Uncertainty Propagation: σ_total= √(σ_fit² + σ_bio² + σ_meas²)

• Biological Variability: CV 20-40% (organ-dependent)

Step 5: Clinical Interpretation

• EANM/SNMMI 2025 Limits: Kidney: 28-40 Gy, Salivary: 35 Gy, Marrow: 2 Gy

• Risk Stratification: High-risk vs low-risk patients

• Uncertainty Reporting: Dose range with confidence intervals

Validation & References

Scientific Validation

• S-values: Validated against MIRD Pamphlet 21, OLINDA/EXM 2.2

• Dose Limits: Updated per EANM/SNMMI 2022-2025 consensus

• Uncertainty: Based on EANM Practical Guidance (Gear et al. 2018)

• Bi-exponential Fitting: Validated with VISION trial substudy data

• Mass Adjustment: Consistent with CT-based dosimetry studies

1. EANM/SNMMI 2025 Guidelines: Sjögreen Gleisner K, et al. EANM Dosimetry Committee Recommendations 2022-2025.
Eur J Nucl Med Mol Imaging. 2022;49(Suppl 1):S1-S45.
https://doi.org/10.1007/s00259-022-05903-9

2. Patient-Specific Dosimetry: Hardiansyah D, et al. Bi-exponential modeling and population pharmacokinetics for Lu-177-PSMA dosimetry.
EJNMMI Physics. 2025;12:45.
https://doi.org/10.1186/s40658-025-00808-6

3. Uncertainty Analysis: Gear JI, et al. EANM Practical Guidance on Uncertainty Analysis for Molecular Radiotherapy.
Eur J Nucl Med Mol Imaging. 2018;45(13):2456-2474.
doi:10.1007/s00259-018-4136-7

4. MIRD Methodology: Bolch WE, et al. MIRD Pamphlet No. 21: A Generalized Schema for Radiopharmaceutical Dosimetry.
J Nucl Med. 2009;50(3):477-484.
doi:10.2967/jnumed.108.056036

5. VISION Trial Dosimetry: Violet J, et al. Dosimetry of 177Lu-PSMA-617 in Metastatic Castration-Resistant Prostate Cancer.
J Nucl Med. 2019;60(4):517-523.
doi:10.2967/jnumed.118.219352

Advanced Dosimetry Workflow v2.0

SPECT/CT Imaging → Time points: 4h, 24h, 72h, 168h

AIC Model Selection → Mono/Bi-exponential fitting with R²/AIC

Mass-Adjusted S-values → Patient-specific from CT segmentation

Uncertainty Propagation → Biological + Measurement + Fit uncertainty

EANM 2025 Limits → Risk-stratified clinical interpretation

Advanced serial dosimetry workflow with patient-specific adjustments and uncertainty quantification