Radiation protection in fixed PET/CT facilities--design and operation

The potential advantages and workflow challenges of long axial field of view PET/CT

Recently developed Long (≥100 cm) axial field of view (AFOV) PET/CT scanners are capable of producing images with higher signal-to-noise ratio, or performing faster whole-body acquisitions, or scanning with lower radiation dose to the patient, compared with conventional PET/CT scanners. These benefits, which arise due to their substantially higher, by more than an order of magnitude, geometric efficiency, have been well described in the recent literature. The introduction of Long AFOV PET/CT technology into the clinic also has important implications for the design and workflow of PET/CT facilities and their effects on radiation exposure to staff and patients. Maximising the considerable benefits of this technology requires a thorough understanding of the relationships between these factors to optimise workflows while appropriately managing radiation exposure. This article reviews current knowledge on PET/CT facility design, workflows and their effects on radiation exposure, identifies gaps in the literature and discusses the challenges that need to be considered with the introduction of Long AFOV PET/CT into the clinic.

Determination of a reliable assessment for occupational eye lens dose in nuclear medicine

The most recent statement published by the International Commission on Radiological Protection describes a reduction in the maximum allowable occupational eye lens dose from 150 to 20 mSv/year (averaged over 5‐year periods). Exposing the eye lens to radiation is a concern for nuclear medicine staff who handle radionuclide tracers with various levels of photon energy. This study aimed to define the optimal dosimeter and means of measuring the amount of exposure to which the eye lens is exposed during a routine nuclear medicine practice. A RANDO human phantom attached to Glass Badge and Luminess Badge for body or neck, DOSIRIS and VISION for eyes, and nanoDot for body, neck, and eyes was exposed to ^99mTc, ¹²³I, and ¹⁸F radionuclides. Sealed syringe sources of each radionuclide were positioned 30 cm from the abdomen of the phantom. Estimated exposure based on measurement conditions (i.e., air kerma rate constants, conversion coefficient, distance, activity, and exposure time) was compared measured dose equivalent of each dosimeter. Differences in body, neck, and eye lens dosimeters were statistically analyzed. The 10‐mm dose equivalent significantly differed between the Glass Badge and Luminess Badge for the neck, but these were almost equivalent at the body. The 0.07‐mm dose equivalent for the nanoDot dosimeters was greatly overestimated compared to the estimated exposure of ^99mTc and ¹²³I radionuclides. Measured dose equivalents of exposure significantly differed between the body and eye lens dosimeters with respect to ¹⁸F. Although accurately measuring radiation exposure to the eye lenses of nuclear medicine staff is conventionally monitored using dosimeters worn on the chest or abdomen, eye lens dosimeters that provide a 3‐mm dose equivalent near the eye would be a more reliable means of assessing radiation doses in the mixed radiation environment of nuclear medicine.

A software-based approach for calculating spatially resolved radiation exposure for structural radiation protection in nuclear medical imaging

The objective of the work described is the development of a software tool to provide the calculation routines for structural radiation protection from positron and gamma emitters, for example,¹⁸F. The calculation of the generated local annual dose in the vicinity of these radioactive sources supports the engineering of structural measures necessary to meet regulatory guidelines. In addition to accuracy and precision, a visual and intuitive presentation of the calculation results enables fast evaluation. Finally, the calculated results are presented in a contour plot for design, evaluation, and documentation purposes. A python program was used to provide the calculation routines for structural radiation protection. For simplicity, the radiating sources can be considered as point sources. The attenuation of structural elements can be specified or, in the case of lead, calculated by virtue of its thickness. The calculated attenuation for the lead shielding is always slightly underestimated, which leads to a marginally higher calculated local dose rate than would be physically present. With the conservatively determined value, the structural radiation protection can be optimised in accordance with the general rule of as low as reasonably achievable. The pointwise comparison between the software results and the standard procedure for calculating the dose of points in space leads to similar values. In comparison with the general approach of calculating single representative points in the radiation protection area, the visual and intuitive presentation of the results supports the design and documentation of the measures required for structural radiation protection. In the present version of the software, the local dose rate and local annual dose are overestimated by a maximum of 4.5% in the case of lead shields. The proposed software, termed RadSoft, was successfully used to develop the structural radiation protection of a controlled area for hybrid magnetic resonance - positron emission tomography imaging, with the focus herein being on the requirements for PET.

DESIGN, COMMISSIONING AND OPERATION OF PROGRAMMABLE DRAINAGE SYSTEM FOR PET-CT: AN OPTIMIZED APPROACH TO PROTECT PERSONNEL AND ENVIRONMENT IN NUCLEAR MEDICINE FACILITIES

Nuclear medicine facilities are considered one of the most important practices associated with potential radiological risks to personnel and the environment due to the significant amounts of solid and liquid radioactive waste generated from these facilities. Whenever possible and applicable, the licensee shall apply the most up-to-date technological advances to ensure that such radioactive waste is safely discharged to the public sewage. To date, there is no specific technical safety requirement endorsed by regulatory body in Egypt regarding drainage system design for nuclear medicine facilities. This paper discusses the design, commissioning and operation of a programmable drainage system in a Positron Emission Tomography/Computed Tomography (PET-CT) unit for collecting and draining sewage contaminated with the radioactive isotope 18F. The system operates automatically without the need for human intervention. The system has been tested using clean water and found to be working efficiently in accordance with the design parameters. The proposed system concept can be applied in other nuclear medicine facilities after scaling it up/down according to all radionuclides in use and the expected volume of associated radioactive waste. Based on the system's demonstrated performance, regulatory bodies are highly recommended to embrace such approach as a safety requirement to assist the licensees in complying with the safety standards during the planning and construction of PET-CT facilities.

A simple, reliable and accurate approach for assessing [131I]-capsule activity leading to significant reduction of radiation exposure of medical staff during radioiodine therapy

PURPOSE

According to German law, the [¹³¹I]-capsule activity has to be checked in the context of radioiodine therapy (RIT) immediately before application. The measurement leads to significant radiation exposure of the medical personnel, especially of their hands. We aimed to establish a method for estimating [¹³¹I]-capsule activity by measuring the dose rate (DR) at contact of the delivered lead closed container carrying the [¹³¹I]-capsules and to evaluate radiation exposure in comparison to conventional [¹³¹I]-capsule measurement using a dose calibrator.

METHODS

DR on the surface of the closed lead container was measured at two locations and correlated linearly with the [¹³¹I]-capsule activity measured in a dose calibrator to create calibrating curves. The hand and whole body (effective) doses were determined with official dose meters during validation of our method in clinical practice.

RESULTS

The determination coefficients (R²) of linear calibration curves were greater than 0.9974. The total relative uncertainty for estimating [¹³¹I]-capsule activity with our method was <±7.5% which is lower than the uncertainty of the nominal activity and quite close to the threshold limit for the maximum allowed uncertainty of ± 5% for measuring activity in radioactive drugs. The reduction of the hand dose caused by our method was 97% compared with the conventional measurements of the [¹³¹I]-capsules in a dose calibrator.

CONCLUSION

Measuring DR on the surface of the closed lead containers enables the [¹³¹I]-capsules activity to be estimated simply, reliably and with sufficient accuracy leading to significant reduction of the radiation exposure for the medical staff.

Radiation Safety and Accidental Radiation Exposures in Nuclear Medicine

Medical radiation accidents and unintended events may lead to accidental or unintended medical exposure of patients and exposure of staff or the public. Most unintended exposures in nuclear medicine will lead to a small increase in risk; nevertheless, these require investigation and a clinical and dosimetric assessment. Nuclear medicine staff are exposed to radiation emitted directly by radiopharmaceuticals and by patients after administration of radiopharmaceuticals. This is particularly relevant in PET, due to the penetrating 511 keV γ-rays. Dose constraints should be set for planning the exposure of individuals. Staff body doses of 1-25 µSv/GBq are reported for PET imaging, the largest component being from the injection. The preparation and administration of radiopharmaceuticals can lead to high doses to the hands, challenging dose limits for radionuclides such as ⁹⁰Y and even ¹⁸F. The risks of contamination can be minimized by basic precautions, such as carrying out manipulations in purpose-built facilities, wearing protective clothing, especially gloves, and removing contaminated gloves or any skin contamination as quickly as possible. Airborne contamination is a potential problem when handling radioisotopes of iodine or administering radioaerosols. Manipulating radiopharmaceuticals in laminar air flow cabinets, and appropriate premises ventilation are necessary to improve safety levels. Ensuring patient safety and minimizing the risk of incidents require efficient overall quality management. Critical aspects include: the booking process, particularly if qualified medical supervision is not present; administration of radiopharmaceuticals to patients, with the risk of misadministration or extravasation; management of patients' data and images by information technology systems, considering the possibility of misalignment between patient personal data and clinical information. Prevention of possible mistakes in patient identification or in the management of patients with similar names requires particular attention. Appropriate management of pregnant or breast-feeding patients is another important aspect of radiation safety. In radiopharmacy activities, strict quality assurance should be implemented at all operational levels, in addition to adherence to national and international regulations and guidelines. This includes not only administrative aspects, like checking the request/prescription, patient's data and the details of the requested procedure, but also quantitative tests according to national/international pharmacopoeias, and measuring the dispensed activity with a calibrated activity meter prior to administration. In therapy with radionuclides, skin tissue reactions can occur following extravasation, which can result in localized doses of tens of Grays. Other relevant incidents include confusion of products for patients administered at the same time or malfunction of administration devices. Furthermore, errors in internal radiation dosimetry calculations for treatment planning may lead to under or over-treatment. According to literature, proper instructions are fundamental to keep effective dose to caregivers and family members after patient discharge below the Dose constraints. The IAEA Basic Safety Standards require measures to minimize the likelihood of any unintended or accidental medical exposures and reporting any radiation incident. The relative complexity of nuclear medicine practice presents many possibilities for errors. It is therefore important that all activities are performed according to well established procedures, and that all actions are supported by regular quality assurance/QC procedures.

The Effects on Technologist Occupational Exposure in PET/CT Departments When Working with Students at Various Levels of Supervision

The purpose of this study was to evaluate the effect that the presence of a student in the PET/CT department has on the technologist's occupational radiation exposure and whether this effect is influenced by the type of supervision performed. Methods: This was a retrospective, institutional review board-approved study that collected data from 2 PET/CT departments. Dosimetry reports, correlated with the clinical schedules of the students, were normalized for workflow (amount of radioactivity), the number of technologists, and the number of monitored days in the department. A 2-sample t test assuming unequal variance with an α of 0.05 was used to compare doses between with-student and without-student groups and between direct-supervision and indirect-supervision groups. Results: The study consisted of a dataset of 42 dosimetry reports, 19 with students and 23 without students. When comparing with-student and without-student groups, the total (n = 42) extremity dose had a P value of 0.012 with a mean of 0.0011665 μSv/MBq/technologist/d; all other dose comparisons between groups were greater than 0.05 (P > 0.05). For indirect supervision (n = 21), the extremity-dose P value was 0.298. The other dose P values were all less than 0.05. For direct supervision (n = 21), the dose P values were all greater than 0.05. There was a trend toward decreasing exposure of technologists when students were in the department. Conclusion: Extremity dose decreases when students are present. There is a trend toward decreasing dose with indirect supervision.

OCCUPATIONAL EXPOSURE FROM F-18-FDG PET/CT: IMPLEMENTATION TO ROUTINE CLINICAL PRACTICE

The purpose of this study was to assess the occupational radiation exposure arising from positron emission tomography combined with X-ray computed tomography (PET/CT) procedures. From 2009 through the end of 2014, in a team of six technologists, personal dosimetry was performed using electronic personal dosemeters and film badge dosemeters. The technologists registered the separate exposure after each PET/CT operational step, which included radiopharmaceutical arrival, dispensing in individual syringes, injection and patient positioning.From the total of 3024 PET/CT procedures, 2142 were available for analysis. The personal dose equivalent for the technologists performing PET/CT ranged from 11.5 nSv/MBq to 23.8 nSv/MBq. Whole-body radiation dose originated mainly from radiopharmaceutical injection (41.5%) and patient positioning (51.1%). The sources of occupational exposure were successfully identified for PET/CT procedures. Record keeping using on-site occupational dosimetry is a useful tool for exposure optimisation.

Evaluation and optimization of occupational eye lens dosimetry during positron emission tomography (PET) procedures

The last recommendations of the International Commission on Radiological Protection for eye lens dose suggest an important reduction on the radiation limits associated with early and late tissue reactions. The aim of this work is to quantify and optimize the eye lens dose associated to nurse staff during positron emission tomography (PET) procedures. PET is one of the most important diagnostic methods of oncological and neurological cancer disease involving an important number of workers exposed to the high energy isotope F-18. We characterize the relevant stages as preparation and administration of monodose syringes in terms of occupational dose. A direct reading silicon dosimeter was used to measure the lens dose to staff. The highest dose of radiation was observed during preparation of the fluorodesoxyglucose (FDG) syringes. By optimizing a suitable vials' distribution of FDG we find an important reduction in occupational doses. Extrapolation of our data to other clinical scenarios indicates that, depending on the work load and/or syringes activity, safety limits of the dose might be exceeded.

Radiation exposure to nuclear medicine staff involved in PET/CT practice in Serbia

The purpose of this work is to evaluate the radiation exposure to nuclear medicine (NM) staff in the two positron emission tomography-computed tomography centres in Serbia and to investigate the possibilities for dose reduction. Dose levels in terms of Hp(10) for whole body and Hp(0.07) for hands of NM staff were assessed using thermoluminescence and electronic personal dosemeters. The assessed doses per procedure in terms of Hp(10) were 4.2-7 and 5-6 μSv, in two centres, respectively, whereas the extremity doses in terms of Hp(0.07) in one of the centres was 34-126 μSv procedure(-1). The whole-body doses per unit activity were 17-19 and 21-26 μSv GBq(-1) in two centres, respectively, and the normalised finger dose in one centre was 170-680 μSv GBq(-1). The maximal estimated annual whole-body doses in two centres were 3.4 and 2.0 mSv, while the corresponding extremity dose in the later one was 45 mSv. Improvements as introduction of automatic dispensing system and injection and optimisation of working practice resulted in dose reduction ranging from 12 up to 67 %.

Optimization of radiation doses received by personnel in PET uptake rooms

Reduction of dose to exposed personnel during positron emission tomography (PET) installation usually relies on physical shielding. While the major contribution of shielding is unquestioned, it is usually the only method applied. Other methods of reduction, such as working procedure optimization, the position of the furniture, and rooms are usually disregarded in these installations. This paper presents a design and work optimization procedure used in a particular institution. The influence on the dose received by personnel due to the positioning of injection chairs, injection room configuration, and working procedures is studied. Using this optimization strategy, it is possible to reduce the technician dose due to patients by a factor of 0.59. Injection room design is much more important for optimizing the received dose than is work-flow management. The influence of the order of patient entrance on received dose was the aspect that produced the smallest variation in received doses. It is recommended that the optimization be carried out for the installation proposed in the design phase, when no additional cost is required, because the position of the doors of the injection rooms depends on the where the injection chairs are situated.