Estimating residence times and their associated errors in patient absorbed-dose calculation

Area of Science:

• Medical physics
• Radiopharmaceutical dosimetry
• Pharmacokinetics

Background:

• Accurate estimation of organ residence times (tau) is critical for internal emitter radiation dosimetry.
• Quantifying uncertainties in these residence times (gamma tau) is essential for reliable patient dose calculations.
• Chimeric anti-CEA monoclonal antibody (cT84.66) is used in radioimmunotherapy, necessitating precise dosimetry.

Purpose of the Study:

• To determine a method for estimating organ residence times (tau) and their associated errors in patient internal emitter radiation dosage calculations.
• To assess the accuracy of activity integrals and other kinetic variables in radiation dosimetry.

Main Methods:

• A modeling algorithm was employed to calculate patient organ uptake data and residence times for chimeric anti-CEA monoclonal antibody (cT84.66).
• Covariance matrix of model parameters and Monte Carlo simulations were utilized to estimate errors in organ residence time (gamma tau).

Main Results:

• Organ residence time errors were found to be model-dependent.
• Errors increased with the number of organs simultaneously modeled during 90Y-cT84.66 radioimmunotherapy calculations.
• The study analyzed data from two patients undergoing radioimmunotherapy.

Conclusions:

• Modeling and Monte Carlo methods offer a general and direct procedure for calculating the accuracy of activity integrals.
• This approach enhances the reliability of mathematical functions involving kinetic variables in radiation dosimetry.
• The findings are applicable to patient-specific radiation dose calculations in internal emitter therapy.