Comparative evaluation of the new MIRDcalc dosimetry software across a compendium of radiopharmaceuticals

Introduction: Historically, diagnostic radiopharmaceutical dosimetry has been assessed via organ-level MIRD schema-style dosimetry formalisms similar to the computational basis for commonly-used software such as OLINDA and IDAC-Dose. Recently, MIRDcalc software was developed to address the need for a freely-available organ-level dosimetry solution which incorporates up-to-date models of human anatomy, addresses uncertainty in radiopharmaceutical biokinetics and patient organ masses, and offers a one-screen user interface as well as quality-assurance tools. The present work describes the validation of MIRDcalc, and secondarily, provides a compendium of radiopharmaceutical dose coefficients (mGy or mSv/MBq) obtained with MIRDcalc.Materials and Methods: Biokinetic data (in the form of time-integrated activity coefficients in MBq-h/MBq) for ~70 currently- and historically-utilized radiopharmaceuticals were obtained from the ICRP Publication 128(1), and subsequently used to compute absorbed dose and effective dose coefficients using multiple software tools including MIRDcalc, OLINDA 2.1(2), and IDAC-Dose 2.1(3). The dose coefficients obtained with MIRDcalc were systematically compared against the other software-derived dose coefficients and those originally presented in ICRP 128.

Results: The substantial differences in organ contours and inter-organ spacing between the phantoms utilized in MIRDcalc (anatomically realistic voxel phantoms) in comparison to those used for derivation of the ICRP 128 dose coefficients (stylized anthropomorphic phantoms) resulted in differences absorbed dose coefficients for most organs in the range of ~10-60%, though there were more pronounced differences for certain organs, notably the urinary bladder wall and bone endosteal surfaces, for many radiopharmaceuticals. These differences were evident for both the adult and pediatric phantoms. Dose coefficients obtained with OLINDA 2.1 (which implements more modern hybrid phantoms) showed better overall agreement with the MIRDcalc results, but with often larger deviations for the urinary bladder wall generally observed for radiopharmaceuticals with pronounced urinary excretion. Agreement with IDAC-Dose 2.1 for the adult phantoms was generally very good, with most organ dose coefficients agreeing within 0-20%, but with more considerable deviations for the lung sub-tissues and lymph nodes.Conclusion: We report comprehensive testing and validation of MIRDcalc software for use within a reference dosimetry paradigm for multiple radiopharmaceuticals and across adult and pediatric phantoms. Dose coefficients computed with MIRDcalc showed overall excellent agreement with other dosimetry software implementing the ICRP 110-series reference adult voxel phantoms, and showed reasonable agreement with dose coefficients derived using stylized phantoms. Future work should expand the scope of the validation approach to include personalized dosimetry calculations. Acknowledgements: We gratefully acknowledge funding from the NIH/NCI Cancer Center Support Grant P30 CA008748 and NIH U01 EB028234.References:1. ICRP Publication 128: Radiation Dose to Patients from Radiopharmaceuticals: a Compendium of Current Information Related to Frequently Used Substances. S. Mattsson, L. Johansson, S. Leide Svegborn, J. Liniecki, D. Noßke, K.Å. Riklund, M. Stabin, D. Taylor, W. Bolch, S. Carlsson, K. Eckerman, A. Giussani, L. Söderberg, S. Valind, 2015.2. Stabin MG, Sparks RB, Crowe E. OLINDA/EXM: The Second-Generation Personal Computer Software for Internal Dose Assessment in Nuclear Medicine. J Nucl Med. 2005;46:1023-1027.3. Andersson M, Johansson L, Eckerman K, Mattsson S. IDAC-Dose 2.1, an internal dosimetry program for diagnostic nuclear medicine based on the ICRP adult reference voxel phantoms. EJNMMI Res. 2017;7:88.

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