MIRDCalc V 1.0 - A community spreadsheet tool for organ-level radiopharmaceutical absorbed dose calculations.

Objectives: Internal radiation dosimetry is critical for the development of new diagnostic imaging radiotracers as well as therapeutic applications where dosimetry can be used to personalize treatments. To support our dynamic and expanding field, widely available, user-friendly tools that enable accurate dosimetry calculations are required. In response to this, we have developed MIRDCalc - an organ-level biodistribution-to-dosimetry calculation software tool, built in the universally available Microsoft EXCEL platform. MIRDCalc has not yet been reviewed or endorsed by the MIRD Committee.

Methods: MIRDCalc can be run on any computer with Excel 2013 or later installed. The database powering MIRDCalc stores all necessary information for implementing biodistribution-to-dosimetry calculations using the MIRD schema and incorporates calculation-specific details for 333 isotopes (ICRP Publication 107), a family of 12 ICRP phantoms with 58 source organs and 44 target organs each. Additional features of mass scaling, error propagation, dynamic remainder-of-body source regions, quality-control checks, and summary graphics are also included. All input and software interactions are provided in a single-screen interface. The intention is to distribute MIRDCalc freely in the medical and dosimetry community, with open source coding.

Results: MIRDCalc has been tested to run independently at multiple sites with no difficulties observed. Given a set of biodistribution data (i.e. time integrated activity coefficients), a user may open the spreadsheet, select the isotope and phantom, enter data, and arrive at a summary dosimetry calculation in a matter of seconds. For purposes of demonstration and preliminary validation, we tested the spreadsheet using a sample case of a typical FDG PET scan dose for a 15-year-old female, using input biodistribution parameters from ICRP Publication 128. The MIRDCalc output of the dosimetry, along with the analogous published estimates reported in ICRP Publication 128, are presented in Table 1. Reasonable agreement between the two datasets, derived using different models, is demonstrated.

Conclusions: We have built a software tool that can access a large database of Monte Carlo-derived S value tables and implement MIRDCalc dosimetry in an easy and user-friendly manner. This tool will be distributed freely in the community to aid with research and dosimetry estimation. The tool can be easily updated with expanded isotopes/phantoms, and provides a framework for future innovation and development of dose calculation methodology and software in the community.