Calculation of the time-integrated activity coefficient (residence time) is a crucial step in dosimetry for molecular radiotherapy. However, available software is deficient in that it is either not tailored for the use in molecular radiotherapy and/or does not include all required estimation methods. The aim of this work was therefore the development and programming of an algorithm which allows for an objective and reproducible determination of the time-integrated activity coefficient and its standard error.
The algorithm includes the selection of a set of fitting functions from predefined sums of exponentials and the choice of an error model for the used data. To estimate the values of the adjustable parameters an objective function, depending on the data, the parameters of the error model, the fitting function and (if required and available) Bayesian information, is minimized. To increase reproducibility and user-friendliness the starting values are automatically determined using a combination of curve stripping and random search. Visual inspection, the coefficient of determination, the standard error of the fitted parameters, and the correlation matrix are provided to evaluate the quality of the fit. The functions which are most supported by the data are determined using the corrected Akaike information criterion. The time-integrated activity coefficient is estimated by analytically integrating the fitted functions. Its standard error is determined assuming Gaussian error propagation. The software was implemented using MATLAB.
To validate the proper implementation of the objective function and the fit functions, the results of NUKFIT and SAAM numerical, a commercially available software tool, were compared. The automatic search for starting values was successfully tested for reproducibility. The quality criteria applied in conjunction with the Akaike information criterion allowed the selection of suitable functions. Function fit parameters and their standard error estimated by using SAAM numerical and NUKFIT showed differences of <1%. The differences for the time-integrated activity coefficients were also <1% (standard error between 0.4% and 3%). In general, the application of the software is user-friendly and the results are mathematically correct and reproducible. An application of NUKFIT is presented for three different clinical examples.
The software tool with its underlying methodology can be employed to objectively and reproducibly estimate the time integrated activity coefficient and its standard error for most time activity data in molecular radiotherapy.
The authors gratefully acknowledge support by the Bundesministerium für Bildung und Forschung (Federal Ministry of Education and Research, BMBF 01EZ1130). The responsibility for contents of this publication is with the authors. The authors declare that they have no conflict of interest.
II.A. From data selection to fitting
II.A.1. Objective function (OF)
II.A.2. Variance models
II.A.3. Fit functions
II.A.4. Starting values
II.B. From fitting to the area under the curve
II.B.1. Model selection
II.B.2. Area under the curve
III.A. Starting values
III.B. Quality test and model selection
III.B.1. Results of examples
III.C. Comparing with SAAM 2 numerical
IV. DISCUSSION AND CONCLUSION
- Computer software
- Magnetic resonance imaging
- Optical inspection
- Radiation therapy
Data & Media loading...
Article metrics loading...
Full text loading...