Bias and precision analysis in curve fitting for hyperthyroidism clinical dosimetry

Area of Science:

• Nuclear medicine
• Medical physics
• Radiopharmacology

Background:

• Accurate internal dosimetry is crucial for effective hyperthyroidism treatment using iodine-131 (¹³¹I)-sodium iodide (NaI).
• Minimizing uncertainties in dosimetry requires optimizing uptake assessment schedules.
• Patient-specific biokinetics influence the reliability of dosimetry calculations.

Purpose of the Study:

• To evaluate how measurement precision and sampling timing affect the bias and precision of time-integrated activity (TIA) estimates.
• To determine optimal uptake assessment schedules for ¹³¹I hyperthyroidism therapy.
• To analyze the impact of different measurement noise levels on TIA calculations.

Main Methods:

• Simulated patient biokinetics using a two-compartment model based on real dosimetry data.
• Introduced variable relative noise to simulated uptake measurements.
• Calculated TIA bias and precision by comparing fitted and true values.

Main Results:

• TIA bias is generally negative and increases with measurement uncertainty for multi-timepoint schemes.
• Uptake assessment schedules of (5, 24, 168)h and (24, 168)h showed comparable bias and precision.
• Achieving TIA precision below 15% with 10% measurement precision requires the final uptake assessment at or after 6 days post-administration.

Conclusions:

• The choice of uptake assessment schedule significantly impacts TIA accuracy and reliability.
• Later uptake assessments are generally preferable for reducing uncertainty.
• Standard methods for uncertainty estimation may overestimate TIA uncertainty when measurement errors are large.