Background
The aim was to review available biokinetic data, collect own experimental data, and propose an updated compartmental model for 2-
18
FFDG in the frame of the revision of the ICRP report on ...dose coefficients for radiopharmaceuticals used in diagnostic nuclear medicine.
Methods
The compartmental model was developed based on published biokinetic data for 2-
18
FFDG. Additional data on urinary excretion in 23 patients (11 males, 12 females) undergoing whole-body PET/CT examinations were obtained within this study. The unknown biokinetic model parameters were derived using the software SAAM II and verified with a modified version of IDAC-Iodide. Dose coefficients for reference adults were calculated with the programme IDAC-Dose 2.1. A dynamic bladder model was employed for urinary bladder dosimetry.
Results
The proposed model consists of following compartments: blood, heart wall, brain, liver, lungs, pancreas, spleen, kidneys, urinary bladder content and a generic pool compartment “Other”. The latter was introduced to account for 2-
18
FFDG in body organ and tissues besides the explicitly modelled ones. The model predictions showed a good agreement with experimental data. Urinary bladder wall received the highest absorbed dose coefficient of 7.5E−02 mGy/MBq under the assumption of initial urine volume of 100 ml, first voiding at 45 min p.i. and 3.75 h voiding intervals thereafter. The effective dose coefficient calculated according to the current dosimetry framework of ICRP amounted to 1.7E−02 mSv/MBq, compared to 1.9E−02 mSv/MBq in ICRP Publication 128.
Conclusion
A compartmental model for 2-
18
FFDG was proposed and will be used to replace the descriptive biokinetic model of ICRP Publication 128. The revised model and the provided dose coefficients are expected to improve reference dosimetry for patients administered with 2-
18
FFDG.
Background
In order to ensure adequate radiation protection of critical groups such as staff, caregivers and the general public coming into proximity of nuclear medicine (NM) patients, it is ...necessary to consider the impact of the radiation emitted by the patients during their stay at the hospital or after leaving the hospital. Current risk assessments are based on ambient dose rate measurements in a single position at a specified distance from the patient and carried out at several time points after administration of the radiopharmaceutical to estimate the whole-body retention. The limitations of such an approach are addressed in this study by developing and validating a more advanced computational dosimetry approach using Monte Carlo (MC) simulations in combination with flexible and realistic computational phantoms and time activity distribution curves from reference biokinetic models.
Results
Measurements of the ambient dose rate equivalent Ḣ
*
(10)
at 1 m from the NM patient have been successfully compared against MC simulations with 5 different codes using the ICRP adult reference computational voxel phantoms, for typical clinical procedures with
99m
Tc-HDP/MDP,
18
FDG and Na
131
I. All measurement data fall in the 95% confidence intervals, determined for the average simulated results. Moreover, the different MC codes (MCNP-X, PHITS, GATE, GEANT4, TRIPOLI-4
®
) have been compared for a more realistic scenario where the effective dose rate
Ė
of an exposed individual was determined in positions facing and aside the patient model at 30 cm, 50 cm and 100 cm. The variation between codes was lower than 8% for all the radiopharmaceuticals at 1 m, and varied from 5 to 16% for the face-to face and side-by-side configuration at 30 cm and 50 cm. A sensitivity study on the influence of patient model morphology demonstrated that the relative standard deviation of Ḣ
*
(10) at 1 m for the range of included patient models remained under 16% for time points up to 120 min post administration.
Conclusions
The validated computational approach will be further used for the evaluation of effective dose rates per unit administered activity for a variety of close-contact configurations and a range of radiopharmaceuticals as part of risk assessment studies. Together with the choice of appropriate dose constraints this would facilitate the setting of release criteria and patient restrictions.
In biological dosimetry, dose-response curves are essential for reliable retrospective dose estimation of individual exposure in case of a radiation accident. Therefore, blood samples are irradiated
...and evaluated based on the applied assay. Accurate physical dosimetry of the irradiation performance is a critical part of the experimental procedure and is influenced by the experimental setup, especially when X-ray cabinets are used. The aim of this study was to investigate variations and pitfalls associated with the experimental setups used to establish calibration curves in biological dosimetry with X-ray cabinets. In this study, irradiation was performed with an X-ray source (195 kV, 10 mA, 0.5 mm Cu filter, dose rate 0.52 Gy/min, 1
and 2
half-value layer = 1.01 and 1.76 mm Cu, respectively, average energy 86.9 keV). Blood collection tubes were irradiated with a dose of 1 Gy in vertical or horizontal orientation in the center of the beam area with or without usage of an additional fan heater. To evaluate the influence of the setups, physical dose measurements using thermoluminescence dosimeters, electron paramagnetic resonance dosimetry and ionization chamber as well as biological effects, quantified by dicentric chromosomes and micronuclei, were compared. This study revealed that the orientation of the sample tubes (vertical vs. horizontal) had a significant effect on the radiation dose with a variation of -41% up to +49% and contributed to a dose gradient of up to 870 mGy inside the vertical tubes due to the size of the sample tubes and the associated differences in the distance to the focal point of the tube. The number of dicentric chromosomes and micronuclei differed by ~30% between both orientations. An additional fan heater had no consistent impact. Therefore, dosimetric monitoring of experimental irradiation setups is mandatory prior to the establishment of calibration curves in biological dosimetry. Careful consideration of the experimental setup in collaboration with physicists is required to ensure traceability and reproducibility of irradiation conditions, to correlate the radiation dose and the number of aberrations correctly and to avoid systematical bias influencing the dose estimation in the frame of biological dosimetry.
Modelling DTPA decorporation of Am in rats Kastl, Manuel; Grémy, Olivier; Miccoli, Laurent ...
BIO Web of Conferences,
2019, Letnik:
14
Journal Article, Conference Proceeding
Introduction
Three‐dimensional printing is a promising technology to produce phantoms for quality assurance and dosimetry in X‐ray imaging. Crucial to this, however, is the use of tissue equivalent ...printing materials. It was thus the aim of this study to evaluate the properties of a larger number of commercially available printing filaments with respect to their attenuation and absorption of X‐rays.
Materials and methods
Apparent kerma attenuation coefficients (AKACs) and absorbed doses for different X‐ray spectra (tube voltages, 70–140 kV) were measured and simulated by Monte‐Carlo computations for a larger number of fused‐deposition‐modeling (FDM) materials. The results were compared with the respective values simulated for reference body tissues. In addition, the properties of polylactide acid samples printed with reduced infill densities were investigated.
Results
Measured and simulated AKACs and absorbed doses agreed well with each other and in case of AKACs also with attenuation coefficients derived from the reference database of the National Institute of Standards and Technology (NIST). For lung, adipose, muscle, and bulk soft tissue as well as for spongiosa (cancellous bone), printed materials with equivalent attenuation as well as absorption properties could be identified. In contrast, none of the considered printed materials was equivalent to cortical bone.
Conclusion
Several FDM materials have been identified as well‐suited substitutes for body tissues in terms of the investigated material characteristics. They can therefore be used for in‐house production of individualized and task‐specific phantoms for image quality assessment and dose measurements in X‐ray imaging.
The impact of the exposure to ionizing radiation in the offspring and next generation has been investigated in the last decades and currently is the subject of study of the ICRP Task Group 121. ...Studying the effects of radiation exposure in pre-conceptional and post-conceptional phases can be a challenge since potential effects to the fetus vary depending on the stage of fetal development. Epidemiology and radiobiology studies are the two sources of information one can use to correlate the radiation dose to the human body and tissues and the resulting effects. For a proper evaluation of the outcomes of such studies, and a correct appraisal of the exposure/dose-effect relationship, (i) reliable dosimetry, (ii) accurate reporting, and (iii) reproducibility of results are required. Although variables related to dose, including for instance source of radiation, geometry of irradiation, dose rate etc., are usually known, especially in radiobiology studies, often important details of the irradiation are not reported.
Based on standards developed by the National Cancer Institute (NCI), the National Institute of Allergy and Infectious Disease (NIAID) and the National Institute of Standards and Technology (NIST), a review of the scientific studies used by the UNSCEAR to estimate the risk of hereditary effects, and by the ICRP in its current recommendations, was conducted to evaluate the way dosimetry was reported. Dosimetry and the related uncertainties were not adequately described in the vast majority of those studies. This does not necessarily mean that they do not provide relevant information, however it prevents from a thorough verification and reproduction of their findings. In order to guarantee the reliability and robustness of the process of revision of the estimates of risk and detriment it is therefore considered mandatory to include a careful check of the new relevant literature with regard to the criteria on the completeness and reproducibility of the dosimetric information.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Radiation doses delivered by incorporated radionuclides cannot be directly measured, and they are assessed by means of biokinetic and dosimetric models and computational phantoms. For emitters of ...short-range radiation like alpha-particles or Auger electrons, the doses at organ levels, as they are usually defined in internal dosimetry, are no longer relevant. Modelling the inter- and intra-cellular radiation transport and the local patterns of deposition at molecular or cellular levels are the challenging tasks of micro- and nano-dosimetry. With time, the physiological and anatomical realism of the models and phantoms have increased. However, not always the information is available that would be required to characterise the greater complexity of the recent models. Uncertainty studies in internal dose assessment provide here a valuable contribution for testing the significance of the new dose estimates and of the discrepancies from the previous values. Some of the challenges, limitations and future perspectives of the use of models and phantoms in internal dosimetry are discussed in the present manuscript.
The aim of this study was to evaluate the relationship between cerium content in human breast milk and blood plasma or serum. Blood samples and breast milk at various stages of lactation, from 5 days ...to 51 weeks post partum, were donated by 42 healthy breast-feeding mothers from Munich, Germany and by 26 lactating Spanish mothers from Madrid at 4 weeks post partum. Inductively coupled plasma mass spectrometry was applied for the determination of cerium in the biological samples. Cerium concentration in the digested milk samples from Munich showed low values and the arithmetic mean values ranged between the quantification limit of 5
ng/L up to 65
ng/L. The median value amounted to 13
ng/L. The cerium concentrations in the Spanish breast milk samples amounted to similar low values. The data were about a factor of eight lower than values found in a former study of samples from an eastern German province. All cerium concentrations in the German plasma samples, except for two, were at the quantification limit of 10
ng/L. Interestingly, the serum samples of the Spanish mothers showed cerium values ranging between 21.6 and 70.3
ng/L; these higher data could be explained by an enhanced intake of cerium by humans in Madrid. This could be caused by increased cerium concentrations in particulate matter due to a higher traffic volume in Madrid compared to Munich.
The results obtained in this study contribute to setting reference baseline values of cerium in human breast milk and blood plasma/serum and indicate a varying cerium amount depending on the cerium environmental pollution. Possibly, the cerium content in plasma/serum could be an indicator for environmental cerium, which is not valid for breast milk.
PDF
