TestDose: Software for creating dosimetry problems

Objectives Software phantoms are useful for validating quantitative image analysis algorithms but creating them can be a demanding task. We have built a software tool to simplify the process.

Methods The software (TestDose) uses a linear compartment model to simulate radiopharmaceutical kinetics. A set of 4D voxel phantoms are used to represent the time-varying spatial distribution of each compartment and of the physical material in the body. TestDose creates projection images of each compartment according to a user-defined, multi-scan, multi-day imaging protocol. Evaluation of the kinetic model yields time-activity curves for each compartment which are used to scale the projections. The scaled images are aggregated and sampled at random to produce the final set of simulated images, which are presented to the user for analysis. The software also computes a reference dose distribution, at the voxel level, by evaluating the kinetic model to obtain cumulated activity per compartment and combining this with a Monte Carlo simulation of the absorbed dose arising from a unit of activity in each compartment.

Results The software has been implemented as a set of Tcl scripts that control the execution of several other software packages. The DNCAT package is used to construct the dynamic voxel phantom. An in-house package is used to evaluate the compartment model representing the tracer kinetics. The OSEM software is used to simulate projection imaging and the EGSnova software is used to calculate absorbed dose distributions. The TestDose suite is modular and will permit alternative packages to be incorporated in the future.

Conclusions The TestDose software has been developed to simplify the process of creating phantoms for image-based radionuclide dosimetry studies, which can extend over many days and may involve several imaging protocols.