Organ dose calculator for diagnostic nuclear medicine patients based on the ICRP reference voxel phantoms and biokinetic models

Abstract

The exponential growth in the use of nuclear medicine procedures represents a general radiation safety concern and stresses the need to monitor exposure levels and radiation-related long term health effects in NM patients. In the current study, following our previous work on NCINM version 1 based on the UF/NCI hybrid phantom series, we calculated a comprehensive library of S values using the ICRP reference pediatric and adult voxel phantoms and established a library of biokinetic data from multiple ICRP Publications, which were then implemented into NCINM version 2. We calculated S values in two steps: calculation of specific absorbed fraction (SAF) using a Monte Carlo radiation transport code combined with the twelve ICRP pediatric and adult voxel phantoms for a number of combinations of source and target region pairs; derivation of S values from the SAFs using the ICRP nuclear decay data. We also adjusted the biokinetic data of 105 radiopharmaceuticals from multiple ICRP publications to match the anatomical description of the ICRP voxel phantoms. Finally, we integrated the ICRP phantom-based S values and adjusted biokinetic data into NCINM version 2. The ratios of cross-fire SAFs from NCINM 2 to NCINM 1 for the adult phantoms varied widely from 0.26 to 5.94 (mean=1.24, IQR=0.77–1.55) whereas the ratios for the pediatric phantoms ranged from 0.64 to 1.47 (mean=1.01, IQR=0.98–1.03). The ratios of absorbed dose coefficients from NCINM 2 over those from ICRP publications widely varied from 0.43 (colon for 99mTc-ECD) to 2.57 (active marrow for 99mTc-MAG3). NCINM 2.0 should be useful for dosimetrists and medical physicists to more accurately estimate organ doses for various nuclear medicine procedures.

Absorbed dose coefficients for adult thyroid cancer patients undergoing radioiodine therapy

“…We extracted S values for I-123, I-124, I-125, and I-131 from the National Cancer Institute dosimetry system for Nuclear Medicine (NCINM) version 2 [5], where a library of S values calculated using the ICRP reference voxel phantoms is embedded. The S values from NCINM2 were rearranged according to the source regions, r S , defined in the iodine biokinetic models and the target region, r T , defined in ICRP Publication 133 [31].…”

“…Thus, the estimation of normal tissue doses for thyroid cancer patients is essential not only for RAI therapy planning but also for estimation and prediction of radiation-induced adverse effects. Methods and tools to accurately estimate normal tissue doses for thyroid cancer patients using anatomical and radionuclide images have been actively developed [4][5][6][7]. However, as patient-specific dosimetry is not always feasible for epidemiological studies, organ dose estimation often relies on population-based anatomical and biokinetic models which are used to derive absorbed dose coefficients (i.e.…”

“…However, the absorbed dose coefficients for RAI provided in ICRP Publication 128 [11] may not be applied to dosimetry for thyroid cancer patients whose iodine biokinetics may be significantly different from that of normal subjects with an intact thyroid gland (addressed below in detail). Moreover, the ICRP dose coefficients provided to date were calculated using mathematical equation-based stylised phantoms [12], which may result in significant over-or under-estimations of absorbed doses [5,[13][14][15][16].…”

“…In individual clinical practices, several attempts were made to estimate absorbed doses for particular patient groups using body burden or blood sample measurements [3][4][5]. However, in these studies, the dose estimations were conducted for limited target regions such as thyroid remnant or bone marrow, and/or little attention was paid to calculating absorbed dose coefficients in compliance with a generalised dosimetry schema of ICRP.…”

131I dose coefficients for a reference population using age-specific models

“…Earlier studies have shown variations in effective doses due to photons, electron [20] and 18 F-FDG [21] estimated using a voxel-based model from those estimated using stylized phantoms. The UF/NCI and PRC phantoms have been used to compute SAF values for electrons and photons of various energies [22][23][24], which in turn are used to compute S values and organ doses for medical intake scenarios [24,25]. These studies only focus on dose computation for medical protection pathways such as intravenous and oral administration, while leaving out the inhalation pathway required for radiological protection.…”