Abstract
BackgroundTo date, the estimated radiation-absorbed dose to organs and tissues in patients undergoing diagnostic examinations in nuclear medicine is derived via calculations based on models of the human body and the biokinetic behaviour of the radiopharmaceutical. An internal dosimetry computer program, IDAC-Dose2.1, was developed based on the International Commission on Radiological Protection (ICRP)-specific absorbed fractions and computational framework of internal dose assessment given for reference adults in ICRP Publication 133. The program uses the radionuclide decay database of ICRP Publication 107 and considers 83 different source regions irradiating 47 target tissues, defining the effective dose as presented in ICRP Publications 60 and 103. The computer program was validated against another ICRP dosimetry program, Dose and Risk Calculation (DCAL), that employs the same computational framework in evaluation of occupational and environmental intakes of radionuclides. IDAC-Dose2.1 has a sub-module for absorbed dose calculations in spherical structures of different volumes and composition; this sub-module is intended for absorbed dose estimates in radiopharmaceutical therapy. For nine specific alpha emitters, the absorbed dose contribution from their decay products is also included in the committed absorbed dose calculations.ResultsThe absorbed doses and effective dose of 131I-iodide determined by IDAC-Dose2.1 were validated against the dosimetry program DCAL, showing identical results. IDAC-Dose2.1 was used to calculate absorbed doses for intravenously administered 18F-FDG and orally administered 99mTc-pertechnetate and 131I-iodide, three frequently used radiopharmaceuticals. Using the tissue weighting factors from ICRP Publication 103, the effective dose per administered activity was estimated to be 0.016 mSv/MBq for 18F-FDG, 0.014 mSv/MBq for 99mTc-pertechnetate, and 16 mSv/MBq for 131I-iodide.ConclusionsThe internal dosimetry program IDAC-Dose2.1 was developed and applied to three radiopharmaceuticals for validation against DCAL and to generate improved absorbed dose estimations for diagnostic nuclear medicine using specific absorbed fraction values of the ICRP computational voxel phantoms. The sub-module for absorbed dose calculations in spherical structures 1 mm to 9 cm in diameter and different tissue composition was included to broaden the clinical usefulness of the program. The IDAC-Dose2.1 program is free software for research and available for download at http://www.idac-dose.org.
Highlights
To date, the estimated radiation-absorbed dose to organs and tissues in patients undergoing diagnostic examinations in nuclear medicine is derived via calculations based on models of the human body and the biokinetic behaviour of the radiopharmaceutical
For radionuclides entering the body by inhalation and ingestion in occupational and environmental exposures, the Dose and Risk Calculation (DCAL) [1] program has been used to derive nuclide-specific dose coefficients published by the International Commission on Radiological Protection (ICRP)
The absorbed dose calculations using DCAL and Internal Dose Assessed by Computer (IDAC)-Dose1.0 were based on the stylised family anatomical phantoms described by Cristy and Eckerman [16] and based on the data given in ICRP Publication 23 for the “Reference Man” [17]
Summary
The estimated radiation-absorbed dose to organs and tissues in patients undergoing diagnostic examinations in nuclear medicine is derived via calculations based on models of the human body and the biokinetic behaviour of the radiopharmaceutical. An internal dosimetry computer program, IDAC-Dose2.1, was developed based on the International Commission on Radiological Protection (ICRP)-specific absorbed fractions and computational framework of internal dose assessment given for reference adults in ICRP Publication 133. It is important to be able to perform valid calculations of the absorbed dose in organs and tissues of the body for persons exposed to external radiation sources and radiation from internally distributed radionuclides. For radionuclides entering the body by inhalation and ingestion in occupational and environmental exposures, the Dose and Risk Calculation (DCAL) [1] program has been used to derive nuclide-specific dose coefficients published by the International Commission on Radiological Protection (ICRP). In IDAC-Dose1.0, radionuclide-specific absorbed dose calculations were interpolated from monoenergetic photon-specific absorbed fractions (SAFs) between 10 and 4 MeV, and electrons were assumed to be locally absorbed
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