Are restrictions to behaviour of patients required following fluorine-18 fluorodeoxyglucose positron emission tomographic studies?

Assessing body dose rate constant and effective body absorption factor in Taiwanese reference phantoms

The self-attenuation of a patient's body is an important factor in nuclear medicine for designing radiation shielding. Taiwanese reference man (TRM) and Taiwanese reference woman (TRW) were constructed to simulate the body dose rate constant and the effective body absorption factor for 18F-FDG, 131I-NaI and 99mTc-MIBI using the Monte Carlo technique. For TRM, the maximum body dose rate constants for 18F-FDG, 131I-NaI and 99mTc-MIBI were 1.26 × 10-1, 4.89 × 10-2 and 1.76 × 10-2 mSv-m2/GBq-h, respectively, at heights of 110, 110 and 100 cm. For TRW, the results were 1.23 × 10-1, 4.75 × 10-2 and 1.68 × 10-2 mSv-m2/GBq-h at heights of 100, 100 and 90 cm. The effective body absorption factors were 32.6, 36.7 and 46.2% for TRM and 34.2, 38.5 and 48.6% for TRW. Regional reference phantoms along with the derived body dose rate constant and effective body absorption factor should be used for determining regulatory secondary standards in nuclear medicine.

The Nuclear Medicine Patient as a Line Source: The Source Length Is Certainly Not the Patient Height, But It Is a Reasonable Approximation

ABSTRACT

Nuclear medicine patients are a source of exposure and should receive instructions to restrict contact time with different categories of people. The calculation of the restriction time requires that the dose rate at a given distance, known from an initial measurement and a whole-body retention function, can be extrapolated at other distances. As a basis for this extrapolation, it has been suggested to consider the patient as a line source. However, the validity of this suggestion is based on a few studies and limited measurement distances. We collected from the literature dose rates of nuclear medicine patients measured at different distances and investigated the robustness of the line source model. The cases of 18 F-FDG exams, 99m Tc bone scan exams, and 131 I for hyperthyroidism treatment and remnants ablation were considered. The data were pooled, different cases of measurement time after administration were considered, and the data were fitted according to the line source model in which the half patient thickness was introduced. It was found that the line source model fits well the data put with a source length that is radionuclide-specific and significantly different from the standard adult height. However, considering a standard source length of 176 cm and neglecting the patient thickness induced at maximum an overestimation by a factor of 2.5 when extrapolating from 1 m to 10 cm. Such an overestimation is not of considerable importance in the calculation of contact restriction times.

Occupational radiation exposures for medical workers in Pakistan – An overview

The imperative use of ionizing radiation in medicine causes the inevitable occupational exposure of the medical workers during the course of routine duties. The magnitude of health risk due to such radiation exposures has been described in terms of occupational radiation doses. In this context, it is obligatory to monitor, measure and document the radiation dose of occupationally exposed medical workers. This study aims to review the whole-body occupational radiation exposures of medical workers in Pakistan. Specifically, online literature published during 2000-2018 was reviewed for the occupational radiation exposures of Pakistani medical workers. Analysis of the extracted personal dosimetry data revealed that the total number of monitored medical occupational workers was 26046. The range of total cumulative and annual average effective doses was 94-15785 Person-mSv and 0.66-7.37 mSv, respectively. A significant number of the workers (25477; ~98%) received an annual dose below 5 mSv, while only 18 workers received an occupational exposure exceeding the annual dose limit of 20 mSv. It is expected that this study will provide a useful reference for evaluating and improving radiation protection and safety policies in the country.

Factors affecting radiation exposure dose in nursing staff during (18)F-fluorodeoxyglucose positron emission tomography/computed tomography

OBJECTIVES

We evaluated factors associated with increased radiation exposure dose in nursing staff who assisted patients with (18)F-fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET)/computed tomography (CT) examinations.

METHODS

The Barthel Index and Mini-Mental State Examination (MMSE) score were obtained before PET/CT examinations in 193 patients (mean age ± SD, 77.7 ± 8.0 yr). Three nurses self-measured their radiation exposure dose while assisting patients during each PET examination. Disturbance factors during PET examinations (use of a stretcher or wheelchair, use of lines or tubes connected to the patient, use of diapers or urethral catheterization, patient age), (18)F-FDG injection dose, and previous PET/CT experience in the patients and outpatient or inpatient status were evaluated as factors possibly associated with increased radiation exposure. Principle component analysis, univariate analysis, and multivariate regression analysis were used for assessing associations between radiation exposure dose and factors.

RESULTS

The mean radiation exposure dose of the nursing staff was 6.07 ± 5.71 µSv per examination. Statistically significant factors associated with increased radiation exposure (<8 or ≥8 µSv/case) in the univariate analysis were the Barthel Index (<75 or ≥75), MMSE score (<22 or ≥22) of the patients, numbers of lines or tubes to the patient, use of a stretcher or wheelchair, and (18)F-FDG injection dose. Multivariate logistic regression modeling showed that the Barthel Index (<75 or ≥75) and MMSE score (<22 or ≥22) of the patients were significant factors in the final model.

CONCLUSIONS

Lower Barthel Indexes (lower ADL) and lower MMSE scores (lower cognitive function) were independent factors associated with increased radiation exposure dose in nursing staff assisting during (18)F-FDG PET/CT.

Estimated dose from diagnostic nuclear medicine patients to people outside the Nuclear Medicine department

Patients undergoing nuclear medicine scans can be a source of radiation exposure for staff, family and the public. In this paper, 12 common nuclear medicine scans are considered. Doses are estimated for a range of scenarios, to hospital staff, to the public and to the patients' co-workers and family. Estimates are based on dose rates measured as patients left the Nuclear Medicine department. Radiopharmaceutical clearance is calculated from biokinetic models described in International Commission on Radiological Protection publications 53, 80 and 106. For all scan types, and all scenarios, doses are estimated to be substantially less than the trigger level of 300 µSv. Within the hospital, Intensive Care Unit staff receive the highest dose (up to 80 µSv) from patients who have had a myocardial scan or a positron emission tomography scan. For out-patients, the highest doses (up to 100 µSv) are associated with travel on public transport (for 4 h) on the same day as the scan.

Measured dose rate constant from oncology patients administered 18F for positron emission tomography

PURPOSE

Patient exposure rate measurements verify published patient dose rate data and characterize dose rates near 2-18-fluorodeoxyglucose ((18)F-FDG) patients. A specific dose rate constant based on patient exposure rate measurements is a convenient quantity that can be applied to the desired distance, injection activity, and time postinjection to obtain an accurate calculation of cumulative external radiation dose. This study reports exposure rates measured at various locations near positron emission tomography (PET) (18)F-FDG patients prior to PET scanning. These measurements are normalized for the amount of administered activity, measurement distance, and time postinjection and are compared with other published data.

METHODS

Exposure rates were measured using a calibrated ionization chamber at various body locations from 152 adult oncology patients postvoid after a mean uptake time of 76 min following injection with a mean activity of 490 MBq (18)F-FDG. Data were obtained at nine measurement locations for each patient: three near the head, four near the chest, and two near the feet.

RESULTS

On contact with, 30 cm superior to and 30 cm lateral to the head, the mean (75th percentile) dose rates per unit injected activity at 60 min postinjection were 0.482 (0.511), 0.135 (0.155), and 0.193 (0.223) μSv∕MBq h, respectively. On contact with, 30 cm anterior to, 30 cm lateral to and 1 m anterior to the chest, the mean (75th percentile) dose rates per unit injected activity at 60 min postinjection were 0.623 (0.709), 0.254 (0.283), 0.190 (0.218), and 0.067 (0.081) μSv∕MBq h respectively. 30 cm inferior and 30 cm lateral to the feet, the mean (75th percentile) dose rates per unit injected activity at 60 min postinjection were 0.024 (0.022) and 0.039 (0.044) μSv∕MBq h, respectively.

CONCLUSIONS

The measurements for this study support the use of 0.092 μSv m(2)∕MBq h as a reasonable representation of the dose rate anterior from the chest of patients immediately following injection. This value can then be reliably scaled to the desired time and distance for planning and staff dose evaluation purposes. At distances closer than 1 m, a distance-specific dose rate constant of 0.367 μSv∕MBq h at 30 cm is recommended for accurate calculations. An accurate patient-specific dose rate constant that accounts for patient-specific variables (e.g., distribution and attenuation) will allow an accurate evaluation of the dose rate from a patient injected with an isotope rather than simply utilizing a physical constant.

Radiation protection for accompanying person and radiation workers in PET/CT

The purposes of the present study are to measure the total radiation doses for the radiation workers and for the accompanying person to the patients in positron emission tomography (PET)/computed tomography (CT) imaging. Urines samples from the patients were collected at 43, 62, 87, 117, 238, 362 min after the 555-MBq (18)flour-fluorodeoxyglucose ((18)F-FDG) injection and activities were measured. Dose rates were recorded using a Geiger-Muller counter and the total radiation doses were measured with using an electronic personnel dosemeter. According to the results here, 18.4 % of (18)F-FDG was excreted in the urine in 117 min after injection. At 117th min after injection, dose rates were determined as 345, 220, 140, 50 and 15 µSv h(-1), at proposed distances. The radiation doses after 117 min were measured as 3.92 mSv at 0.1 m, 2.11 mSv at 0.25 m and 1.08 mSv at 0.5 m. In conclusion, radiation protection will be sufficient within 2 h after (18)F-FDG injection for PET/CT imaging in daily practice.

AAPM Task Group 108: PET and PET/CT Shielding Requirements

The shielding of positron emission tomography (PET) and PET/CT (computed tomography) facilities presents special challenges. The 0.511 MeV annihilation photons associated with positron decay are much higher energy than other diagnostic radiations. As a result, barrier shielding may be required in floors and ceilings as well as adjacent walls. Since the patient becomes the radioactive source after the radiopharmaceutical has been administered, one has to consider the entire time that the subject remains in the clinic. In this report we present methods for estimating the shielding requirements for PET and PET/CT facilities. Information about the physical properties of the most commonly used clinical PET radionuclides is summarized, although the report primarily refers to fluorine-18. Typical PET imaging protocols are reviewed and exposure rates from patients are estimated including self-attenuation by body tissues and physical decay of the radionuclide. Examples of barrier calculations are presented for controlled and noncontrolled areas. Shielding for adjacent rooms with scintillation cameras is also discussed. Tables and graphs of estimated transmission factors for lead, steel, and concrete at 0.511 MeV are also included. Meeting the regulatory limits for uncontrolled areas can be an expensive proposition. Careful planning with the equipment vendor, facility architect, and a qualified medical physicist is necessary to produce a cost effective design while maintaining radiation safety standards.

Concurrent PET/CT with an Integrated Imaging System: Intersociety Dialogue from the Joint Working Group of the American College of Radiology, the Society of Nuclear Medicine, and the Society of Computed Body Tomography and Magnetic Resonance

Rapid advances in imaging technology are a challenge for health care professionals, who must determine how best to use these technologies to optimize patient care and outcomes. Hybrid imaging instrumentation, combining 2 or more new or existing technologies, each with its own separate history of clinical evolution, such as PET and CT, may be especially challenging. CT and PET provide complementary anatomic information and molecular information, respectively, with PET giving specificity to anatomic findings and CT offering precise localization of metabolic activity. Historically, the acquisition and interpretation of the 2 image sets have been performed separately and very often at different times and locales. Recently, integrated PET/CT systems have become available; these systems provide PET and CT images that are acquired nearly simultaneously and are capable of producing superimposed, coregistered images, greatly facilitating interpretation. As the implementation of this integrated technology has become more widespread in the setting of oncologic imaging, questions and concerns regarding equipment specifications, image acquisition protocols, supervision, interpretation, professional qualifications, and safety have arisen. This article summarizes the discussions and observations surrounding these issues by a collaborative working group consisting of representatives from the American College of Radiology, the Society of Nuclear Medicine, and the Society of Computed Body Tomography and Magnetic Resonance.

Patient self-attenuation and technologist dose in positron emission tomography

Positron emission tomography (PET), with 511-keV radiation and long patient-uptake times, presents unique radiation safety concerns. This two-part study considers aspects of PET radiation safety as they relate to PET suite design, dose to the public, and technologist occupational dose. In the first part of the study, the self-attenuation of radiation by patients' bodies was quantified. The radiation exposure was measured at three positions from 64 patients injected with fluorine-18 fluorodeoxyglucose (FDG) during the uptake period. Compared with an in vitro control used as a point source, a significant decrease in exposure (>40% at 1 m) was observed due to nonuniform distribution of FDG and attenuation within the patients. The attenuation data are consistent with results from simulations [M. E. Phelps, "Comments and Perspectives," J. Nucl. Med. 45, 1601 (2004)] that treat the body as a uniform, water-filled cylinder. As distance is often the principal source of protection for 511-keV radiation, the considerable self-attenuation may allow for more compact PET suites. However, despite high patient self-attenuation, shielding, and standard precautionary measures, PET technologist occupational doses can remain quite high (approximately 12 mSv/year). The second part of this study tracked the daily dose received by PET technologists. Close technologist-patient interaction both during and following FDG administration, as much as 20 min/study, contribute to the high doses and point to the need for a more innovative approach to radiation protection for PET technologists.