IDAC-Dose 2.1, an internal dosimetry program for diagnostic nuclear medicine based on the ICRP adult reference voxel phantoms

Abstract

Background: 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. 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.

Results: The 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.

Conclusions: The 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 .

Keywords: DCAL; Diagnostic nuclear medicine; Effective dose; ICRP; IDAC; Internal dosimetry; Radiopharmaceuticals.

Fig. 1

Example of the IDAC-Dose2.1 interface. Left, radionuclide ¹⁸F has been selected as an example and the cumulated activity per administered activity given in hours from the biokinetic model of ¹⁸F-FDG in ICRP Publication 128 [9]. Right, the list of all source regions that can be selected in the program

Fig. 2

Using IDAC-Dose2.1 to calculate absorbed dose. Left, absorbed dose (in mGy) for the organs and tissues included in the list of tissues with a weighting factor in ICRP Publication 103 and the effective dose as defined in ICRP Publications 60 and 103 (in mSv) together with the absorbed dose to the lens of the eye for the biokinetic model of the intravenous administration of 290 MBq of ¹⁸F-FDG based on the biokinetic model presented in ICRP Publication 128 [9]. Right, the 47 possible target regions for which absorbed doses are calculated

Fig. 3

The module to calculate the absorbed dose to various types of spheres. Left, in this example, a “bone cortical” sphere volume of 10 cm³ was selected. Right, the activity of ²²⁷Th (in MBq). The absorbed dose to the sphere was calculated as 110 Gy (563 Gy including the absorbed dose contribution of daughters) for an administration of 1 MBq ²²⁷Th and an integration period of 80 days (T _D = 1920 h)