SSG-46 Radiation Protection and Safety in Medical Uses of Ionizing Radiation

Establishing an effective legal and regulatory framework for protection and safety in all exposure situations.

Establishing legislation that meets specified requirements.

Establishing an independent regulatory body with the necessary legal authority, competence and resources.

Establishing requirements for education and training in protection and safety.

Ensuring that arrangements are in place for:

• The provision of technical services (including radiation monitoring services and standards dosimetry laboratories);

• Education and training services.

In radiography: air kerma–area product, incident air kerma or entrance surface air kerma (which includes backscatter).

In fluoroscopy: air kerma–area product.

In CT: CT air kerma index and CT air kerma–length product.

In mammography and tomosynthesis: incident air kerma or entrance surface air kerma and mean glandular dose.

In dentistry: incident air kerma for intraoral radiography and air kerma–area product for panoramic radiography and CBCT.

In image guided interventional procedures: air kerma–area product and cumulative reference air kerma at the patient entrance reference point.

Generic justification of radiological procedures;

Justification of radiological procedures in health screening programmes;

Criteria for the justification of radiological procedures for health assessment of asymptomatic individuals intended for the early detection of disease, but not as part of a health screening programme.

The use of a diagnostic radiological procedure to assess the efficacy of the treatment under investigation (e.g. ranging from a DXA scan to measure bone mineral density before, during and after a given treatment regime, to a CT or a positron emission tomography (PET)–CT examination to assess some clinical indicators, again performed before, during and after the treatment);

Trials being performed to assess a new radiopharmaceutical (i.e. the radiation itself is part of the research, rather than a tool for assessment);

Trials being performed to assess a new radiotherapy protocol alone or in combination with other therapeutic modalities;

Trials being performed to compare radiological procedures, for example specificities and sensitivities of different imaging procedures or efficacy of different treatments;

Trials being performed to assess physiological and/or biochemical processes in healthy individuals. In making its decision, the ethics committee should be presented with correct information on the expected doses and estimates of the radiation risks based on the age, sex and health status of the participants. The ethics committee should also obtain information on who will perform the radiological procedures and how. The dose estimates and the associated radiation risks should be assessed by a medical physicist. This information should be then considered by the ethics committee together with the information on the other risks and benefits of the programme.

A barrier should be placed at the control console to shield staff to the extent that they do not need to wear protective clothing while at the console. This is particularly important in mammography, where structural shielding in walls, ceiling and floor might not be deemed necessary.

In radiography, all possible intended directions of the X ray beam should be taken into consideration in the room design so that the X ray beam cannot be directed at any area that is not shielded and which could lead to potentially unacceptable doses being received in this area.

The doors should provide protective shielding for secondary radiation and should be shut when the X ray beam is on. In radiography, the X ray room should be designed so as to avoid the direct incidence of the X ray beam on the access doors.

The medical radiation technologist should be able to clearly observe and communicate with the patient at all times during an X ray diagnostic procedure.

Mobile facilities should be built so that protection is optimized mainly through shielding (in all relevant directions during use), as providing protection through distance is often limited and exposure time is determined by the procedure being performed.

An appropriate power supply should be available with reliable connections.

Entrance to the mobile facility should be under the control of the mobile facility personnel.

Waiting areas, if they exist, should be appropriately shielded to afford levels of protection consistent with public exposure limits. Waiting areas are common for mobile mammography facilities but not for mobile CT facilities.

To facilitate the imaging procedure, including patient flow, mobile CT facilities are usually operated adjacent to a hospital or clinic, from where they can draw water and electricity, and where patients can use the toilets, waiting rooms and changing rooms and have access to physician offices. Similarly, mobile mammography facilities may also utilize hospital or clinic facilities.

The dose that would be received without shielding is calculated by using workload values, use factors for a given beam direction (the fraction of the total amount of radiation emitted in that direction) and occupancy factors (the fraction of the total exposure that will actually affect individuals at a place, by virtue of the time spent by an individual in that place). For secondary barriers, the use factor is always unity, since scatter and leakage radiation is propagated in all directions all the time. If tabulated figures are used, care should be taken that they reflect the actual usage in the facility and not generic national scenarios. Potential changes in practice and increases in workload should be considered as part of the calculations.

Once the dose that would be received without shielding is known, attenuation should be calculated to reduce this dose to a design level that meets national regulations and that can be considered optimized protection; that is, a dose below which additional cost and effort in shielding is not warranted by the dose being averted. This may require successive calculations to determine where this level lies.

For primary barriers, the attenuation by the patient and image receptor is not considered.

Workload, use and occupancy factors are overestimated.

Staff members are always in the most exposed place of the room.

Distances are always the minimum possible.

Leakage radiation is the maximum all the time.

Field sizes used for the calculation of scatter radiation are overestimated.

Attenuation of the materials is usually considered for the maximum beam quality used.

The numerical value of calculated air kerma (in mGy) is directly compared with dose limits or dose constraints (in mSv), which are given in terms of effective dose. However, the actual effective dose to personnel or members of the public is substantially lower than the air kerma, given the dose distribution within the body for the beam qualities used in diagnostic and interventional radiology.

Means to detect immediately any malfunction of a single component of the system that may lead to an inadvertent underexposure or overexposure of the patient or exposure of staff so that the risk of any unintended or accidental medical exposure is minimized.

Means to minimize the frequency of human error and its impact on the delivery of unintended or accidental medical exposure.

Hardware and software controls that minimize the likelihood of unintended or accidental medical exposures.

Operating parameters for radiation generators, such as the generating tube potential, filtration, focal spot position and size, source to image receptor distance, field size indication and either tube current and time or their product, that are clearly and accurately shown.

Radiation beam control mechanisms, including devices that indicate clearly (visually and/or audibly) and in a fail-safe manner when the beam is on.

X ray tubes with inherent and added filtration adequate to remove low energy components of the X ray beam which do not provide diagnostic information.

Collimating devices to define the radiation beam; in the case of a light beam diaphragm, the light field should align with the radiation field.

With the exception of mammography, dental X ray and CT equipment, diagnostic and interventional X ray equipment that is fitted with continuously adjustable beam collimating devices. Such devices allow the operator²⁰ to limit the area being imaged to the size of the selected image receptor or the region of interest, whichever is the smaller.

When preset protocols are provided, technique factors that are readily accessible and modifiable by adequately trained personnel.

Design of the X ray tube to keep radiation leakage as low as reasonably achievable and not exceeding 1 mGy in an hour measured at 1 m from the focal spot, and less than maximum levels specified in international standards or in local regulations.

The provision of devices that automatically terminate the irradiation after a preset time, tube current–exposure time product, or dose to the automatic exposure control (AEC) detector, or when the ‘dead man’ hand switch is released.

The incorporation of AEC systems in radiographic units, where practicable. Such AEC systems should be able to compensate for energy dependence, patient thickness and dose rate, for the expected range of clinical imaging conditions, and should be suited to the type of image receptor being used, whether film–screen or digital.

Indications or displays of the air kerma–area product and/or incident air kerma.

A minimum tube potential of 60 kV_p;

For intraoral dental systems, an open-ended (preferably rectangular) collimator providing a focus to skin distance of at least 20 cm and a field size at the collimator end of no more than 4 cm × 5 cm if rectangular or 6 cm in diameter if cylindrical, and limitation of field size to the dimensions of the image receptor;

For panoramic dental systems, limitation of field size to the area required for diagnosis by means of programmed field size trimming and the ‘child imaging mode’;

For dental CBCT, adjustable X ray tube potential and tube current–exposure time product, and a choice of volume sizes and voxel sizes.

Console display of all CT parameters that directly influence the image acquisition (these can be displayed over a number of screens);

Console display of estimated volume CT air kerma index and CT air kerma–length product for the procedure or image acquisition;

Operator alert if exposure factors are set too high (usually expressed in terms of the volume CT air kerma index and/or the CT air kerma–length product);

Means for dose modulation (rotational and z-axis), and means for selection of noise index or equivalent;

A comprehensive range of beam widths and pitches and other ancillary devices (e.g. dynamic collimation) to ensure ‘over ranging’ in CT is kept as low as reasonably achievable by facilitating the appropriate choice of beam width and pitch to limit patient dose while maintaining diagnostic image quality;

Reconstruction algorithms that result in dose reduction without compromising image quality, such as iterative reconstruction algorithms;

A range of selectable tube potentials, tube current–exposure time products, and filters to facilitate the optimization of protocols, especially for children.

Specific design features for medical radiological equipment used for mammography (both digital systems and film–screen systems) should include the following:

Various anode and filter combinations;

Compression and immobilization capabilities;

Magnification views;

Display on the console of a dose index, for example incident air kerma or mean glandular dose;

An image receptor or image receptors to accommodate all breast sizes.

The provision of a device that energizes the X ray tube only when continuously depressed (such as an exposure foot switch or ‘dead man’ switch);

Indications or display (both at the control console and on monitors) of the elapsed time, air kerma–area product, and cumulative reference air kerma;

Automatic brightness control (ABC) or automatic dose rate control (ADRC);

Pulsed fluoroscopy and pulsed image acquisition modes;

The capture and display of the last acquired frame (last image hold);

Interlocks that prevent inadvertent energizing of the X ray beam when the image detector is removed from the imaging chain;

The capability to deactivate the exposure foot switch between cases;

The provision of a timer and an alarm that sounds at the end of a pre-set interval (typically 5 min).

X ray tubes that have high heat capacities to enable operation at high tube currents and short times.

A radiation generator with a capability of at least 80 kW.

A radiation generator with a large dynamic range of tube current and tube potential (to minimize the pulse width necessary to accommodate differences in patient attenuation).

For paediatric work:

• A radiation generator that supports an X ray tube with a minimum of three focal spots;

• An anti-scatter grid that is removable;

• An image acquisition frame rate that extends up to at least 60 frames per second for small children.

A real time display of air kerma–area product and cumulative reference air kerma.

Imaging detectors that allow different fields of view (magnification) to improve spatial resolution.

Automatic collimation.

Dual-shape collimators incorporating both circular and elliptical shutters to be used to modify the field for collimation along cardiac contours.

System specific variable filtration in the X ray beam that is applied according to patient attenuation (often as part of the ADRC system).

Selectable dose per pulse and selectable number of pulses per second.

Wedge filters that move automatically into the field of view to attenuate the beam in areas where there is no tissue and thus no need for imaging.

Possible means for manipulation of diaphragms while in ‘last image hold’.

The option of the automatic display of the last acquired image run.

Display and recording in a dose report in digital format of the following parameters:

• Reference air kerma rate;

• Cumulative reference air kerma;

• Cumulative air kerma–area product;

• Cumulative time of fluoroscopy;

• Cumulative number of image acquisitions (acquisition runs and frames per run);

• Integrated reference air kerma;

• Option for digital subtraction angiography;

• Road mapping, which is a technique used for navigation of the catheter or wire in endovascular procedures.

Real time dose display and end-of-case dose report (radiation dose structured report, DICOM object), including export of dose metrics for the purpose of DRLs and individual patient dose calculation;

Connectivity to RIS and to PACS.

Capability of very short exposure times for radiography;

Specifically designed AEC systems;

Provision of ‘paediatric modes’ for the automatic brightness and/or dose rate control systems in fluoroscopy and image guided interventional procedures;

Paediatric protocols for CT;

Child imaging mode for dental panoramic and CBCT equipment.

The X ray tube should not be pointed at the control console area.

Given that the patient is the source of scatter radiation, care should be taken to ensure that the position of the patient is as far from the control console as is feasible, with account taken of the room configuration and accessories, and preferably more than 1 m distant from the console.

Operators should wear lead aprons and should maintain as much distance as possible between themselves and the patient (to minimize exposure to scatter radiation), whilst still maintaining good visual supervision of the patient and being able to communicate verbally with him or her.

Other staff (e.g. nursing, medical and ancillary staff) are not considered as occupationally exposed workers and hence should be afforded protection as a member of the public. This is achieved by ensuring such persons are as far away from the patient as possible during the exposure (typically at least 3 m) or are behind appropriate barriers.

In situations in which a member of staff needs to be close to the patient, protective aprons should be worn (e.g. an anaesthetist with a ventilated patient or a nurse with an unstable patient).

Verbal warning of an imminent exposure should be given.

Consideration should be given to other patients nearby (see also para. 3.276 on public radiation protection).

Lead aprons should be worn by staff members who need to be adjacent to the patient being exposed.

The primary beam should be directed away from staff and other patients whenever possible.

Staff should keep as far away as possible from the patient during exposure, whilst still maintaining good visual supervision of the patient.

Where available, mobile shields should be used.

Any pregnant staff member (other than radiology staff) should be asked by the medical radiation technologist to leave the vicinity during exposure.

Verbal warning of imminent exposure should be given.

In the case of CT interventions, the interventionist should use appropriate personal protective equipment (a protective apron, a thyroid shield and protective eyewear). In addition, care should be exercised to avoid the placing of hands in the primary beam and immediate notification to the interventionist should be given if this happens.

In the case of persons providing medical support (e.g. anaesthetists), a protective apron should be worn and the person should position themselves as far from the gantry as possible, whilst still maintaining good visual supervision of the patient.

The staff member performing the procedure should use personal protective equipment (a protective apron, a thyroid shield, protective eyewear and gloves). In addition, care should be exercised to avoid the placing of hands in the primary beam and immediate notification to the fluoroscopist should be given if this happens.

In the case of persons providing medical support (e.g. anaesthetists), a protective apron should be worn and the person should position themselves as far from the patient as possible during exposure.

The staff member performing the procedure should use personal protective equipment (a protective apron, a thyroid shield, protective eyewear and gloves). In addition, care should be exercised to avoid the placing of hands in the primary beam and immediate notification to the fluoroscopist should be given if this happens.

Only essential staff should remain in the room. All such staff are considered occupationally exposed workers.

In situations in which a member of staff needs to be close to the patient, protective aprons should be worn (e.g. an anaesthetist with a ventilated patient or a nurse with an unstable patient). At no time should a pregnant staff member take on this role.

Personal protective equipment is not usually needed. Radiation protection is afforded through the use of distance from the patient. Typically, a distance of at least 2 m is recommended.

The operator should not hold the image receptor during the exposure.

Handheld portable X ray equipment for intraoral radiography should be used only for examinations where it is impractical or not medically acceptable to transfer patients to a fixed unit or to use a mobile unit (e.g. in nursing homes, residential care facilities or homes for persons with disabilities; in forensic odontology; or for military operations abroad without dental facilities) [116].

From the neck down to at least 10 cm below the knees;

The entire breast bone (sternum) and shoulders;

The sides of the body from not more than 10 cm below the armpits to at least halfway down the thighs;

The back from the shoulders down to and including the buttocks.

Ceiling suspended protective screens for protecting eyes and the thyroid while keeping visual contact with the patient. Technical advances with such screens include systems that move with the operator.

Protective lead curtains or drapes mounted on the patient table.

Mobile shields either attached to the table (lateral shields) or mounted on coasters (full body).

Disposable protective drapes for the patient.

The room and shielding construction has been completed, regardless of whether it is a new construction or a renovation, and before the room is first used clinically;

New or substantially refurbished equipment is commissioned (both direct and indirect radiation such as leakage and scatter radiation should be measured);

New software for the medical radiological equipment is installed or there is a significant upgrade;

New techniques are introduced;

Servicing of the medical radiological equipment has been performed, which could have an impact on the radiation delivered.

If the monitored worker never wears a protective apron, the dosimeter should be worn on the front of the torso between the shoulders and the waist.

If the monitored worker sometimes wears a protective apron, the dosimeter should be worn on the front of the torso between the shoulders and the waist, and under the apron when it is being worn.

If the monitored worker always wears a protective apron, the dosimeter should be worn on the front of the torso at shoulder or collar level outside the apron (see also para. 3.113), except if national regulations require the dosimeter to be worn under the apron.

If the working situation is such that the radiation always or predominantly comes from one side of the person, such as in image guided interventional procedures, the dosimeter should be placed on the front of the torso on the side closest to the source of radiation; the guidance in (a) to (c) should also be followed in this case.

A single dosimeter placed under the apron, reported in H_p(10), provides a good estimate of the contribution to the effective dose of the parts of the body protected by the apron, but underestimates the contribution of the unprotected parts of the body (the thyroid, the head and neck, and the extremities).

A single dosimeter worn outside the apron, reported in H_p(10), provides a significant overestimate of effective dose and should be corrected for the protection afforded by the apron by using an appropriate algorithm [120, 122, 123].

Where two dosimeters are worn, one under the apron and the other outside the apron, an algorithm should be applied to estimate the effective dose from the two reported values of H_p(10) [120, 122].

Has it already been done? A radiological procedure that has already been performed within a reasonable time period (depending on the procedure and clinical question) should not be repeated (unless the clinical scenario indicates the appropriateness of repeating the procedure). The results (images and reports) of previous examinations should be made available, not only at a given radiology facility but also for consultation at different facilities. Digital imaging modalities and electronic networks should facilitate this process. Individual patient exposure records should be used to facilitate the decision making process if available.

Is it needed? The anticipated outcome of the proposed radiological procedure (positive or negative) should influence the patient’s management.

Is it needed now? The timing of the proposed radiological procedure in relation to the progression of the suspected disease and the possibilities for treatment should all be considered as a whole.

Is this the best investigation to answer the clinical question? Advances in imaging techniques are taking place continually, and the referring medical practitioner may need to discuss with the radiological medical practitioner what is currently available for a given problem.

Has the clinical problem been explained to the radiological medical practitioner? The medical context for the requested radiological procedure is crucial for ensuring the correct technique is performed with the correct focus.

Owing to the higher radiosensitivity of the embryo or fetus, it should be ascertained whether a female patient is pregnant before an X ray examination for diagnosis or an image guided interventional procedure is performed. Paragraph 3.176 of GSR Part 3 [3] requires that procedures be “in place for ascertaining the pregnancy status of a female patient of reproductive capacity before the performance of any radiological procedure that could result in a significant dose to the embryo or fetus”. Pregnancy would then be a factor in the justification process and might influence the timing of the proposed radiological procedure or a decision as to whether another approach to treatment is more appropriate. Confirmation of pregnancy could occur after the initial justification and before the radiological procedure is performed. Repeat justification is then necessary, with account taken of the additional sensitivity of the pregnant patient and embryo or fetus.

As children are at greater risk of incurring radiation induced stochastic effects, paediatric examinations necessitate special consideration in the justification process.

There should be an effective system for correct identification of patients, with at least two, preferably three, forms of verification, for example name, date of birth, address and medical record number.

Patient details should be correctly recorded, such as age, sex, body mass, height, pregnancy status, current medications and allergies.

The clinical history of the patient should be reviewed.

CT air kerma index, usually in mGy. In many States, the more colloquial term computed tomography dose index (CTDI) is used, and is accepted by the ICRU [12].

Weighted CT air kerma index, usually in mGy, which is the CT air kerma calculated from measurements at the centre and periphery of a standard polymethylmethacrylate CT head or body phantom. As in (a), this quantity is often simply called the weighted CTDI.

Volume CT air kerma index, usually in mGy, which takes into account the helical pitch or axial scan spacing. As in (a), this quantity is often simply called volume CTDI.

CT air kerma–length product, usually in mGy·cm. In many States, the more colloquial term dose–length product is used, and is accepted by the ICRU [12].

Radiography: head, chest, abdomen and pelvis.

CT: head, chest, abdomen and pelvis, for specified clinical indications.

Fluoroscopy: barium swallow and barium enema.

Mammography: craniocaudal and mediolateral oblique.

Dentistry: intraoral, panoramic and CBCT.

Bone densitometry (DXA): spine and hip.

Estimations based on incident air kerma or entrance surface air kerma measurements corrected for the techniques used (e.g. X ray tube potential, current and time, and source–skin distance). This approach can be used in radiography (medical and dental), fluoroscopy and mammography.

Estimations based on measured air kerma–area product. This approach can be used in radiography (medical and dental), fluoroscopy and CBCT.

Estimations based on measurements of CT air kerma index and CT air kerma–length product. This approach can be used for CT.

Reported values of dose quantities from DICOM headers or the DICOM radiation dose structured reports. The accuracy of the reported dose quantities should have been validated in acceptance testing and commissioning and by means of quality assurance procedures as explained in para. 3.244. This approach is applicable to all digital modalities.

Direct measurements for selected organs, such as the skin for interventional procedures. For this, thermoluminescent dosimeters and optical stimulated luminescent dosimeters as well as radiochromic or silver halide film can be used.

In the case of CT, size specific dose estimates can be made, where CT air kerma index values are corrected by taking into consideration the size of the patient using linear dimensions measured on the patient or patient images [12, 177].

Methods to avoid the need for holding patients, for example the administration of sedatives (especially for long procedures such as CT examinations) and the use of infant restraints.

Criteria specifying which carers and comforters are allowed to hold patients, for example friends and relatives, provided that they are not pregnant, but not employees of the facility, such as porters and nurses (see also para. 2.49).

Methods for positioning and protecting the carer or comforter so that his or her exposure is as low as reasonably achievable, for example by ensuring that the carer or comforter is not in the direct beam of the radiation device and that appropriate personal protective equipment is used, for example a protective apron or ancillary shields of a specified lead equivalence.

The values of the dose constraints to be applied (see para. 2.49) depend on the radiological exam or intervention; a common value is 5 mSv per event, as stated in para. 2.49. Although it is unlikely that a child, such as a child closely related to the patient, would be a carer or comforter for a diagnostic radiological procedure, in cases where this is unavoidable, his or her dose should be constrained to less than 1 mSv.

The introduction of safety barriers at identified critical points in the process, with specific quality control checks at these points. Quality control should not be confined to physical tests or checks but can include actions such as the correct identification of the patient.

Actively encouraging a culture of always working with awareness and alertness.

Providing detailed protocols and procedures for each process.

Providing sufficient staff who are educated and trained to the appropriate level, and an effective organization, ensuring reasonable patient throughput.

Continuous professional development and practical training and training in applications for all staff involved in providing radiology services.

Clear definitions of the roles, responsibilities and functions of staff in the radiology facility that are understood by all staff.

Allocation of responsibilities to appropriately qualified health professionals only and ensuring that a management system is in place that includes radiation protection and safety;

Use of the lessons from unintended and accidental medical exposures to test whether the management system, including for radiation protection and safety, is robust enough against these types of event;

Identification of other latent risks by posing the questions ‘What else could go wrong?’ or ‘What other potential hazards might be present?’ in a systematic, anticipative manner for all steps in the diagnostic and image guided interventional radiology process.

The requirements for public exposure are satisfied and such exposure is assessed;

Appropriate records of the results of the monitoring programmes are kept.

New or modified medical radiological equipment or accessories are introduced;

Operational changes occur, including changes in workload;

Operational experience or information on accidents or errors indicates that the safety assessment should be reviewed.

Defence in depth measures to cope with events identified in the safety assessment, and evaluation of the reliability of the safety systems (including administrative and operational procedures, equipment and facility design).

Operational experience and lessons from accidents and errors. This information should be incorporated into the training, maintenance and quality assurance programmes.

Means to prevent access by unauthorized persons;

Adequate storage space for equipment used in the given room or area to be available at all times to minimize the potential for spreading contamination to other areas;

A contained workstation for easy decontamination;

Shielded storage for radioactive sources;

Shielded temporary storage for both solid and liquid radioactive waste, and places designated for the authorized discharge of liquid radioactive effluent;

Shielding to protect workers where significant external exposure might occur;

A wash-up area for contaminated articles, such as glassware;

An entry area where protective clothing can be stored, put on and taken off, and which is provided with a hand washing sink and a contamination monitor;

Taps and soap dispenser that are operable without direct hand contact and disposable towels or a hot air dryer;

An emergency eyewash, installed near the hand washing sink;

An emergency shower for decontamination of persons.

Tools for maximizing the distance from the source, for example tongs and forceps;

Syringe shields;

Containers for radioactive materials, with shielding as close as possible to the source;

Double walled containers (with an unbreakable outer wall) for liquid samples;

Drip trays for minimizing the spread of contamination in the case of spillage;

Disposable tip automatic pipettes (alternatively, hypodermic syringes to replace pipettes);

Lead walls or bricks for shielding;

Lead barriers with lead glass windows;

Barriers incorporating a low atomic number material (i.e. acrylic) for work with beta emitters;

Radiation and contamination monitoring equipment (surface and air);

P.Shielded carrying containers, wheeled if necessary, for moving radioactive materials from place to place;

Equipment to deal with spills (decontamination kits).

Radionuclide purity;

Specific activity;

Radiochemical purity;

Chemical purity;

Pharmaceutical aspects, such as toxicity, sterility and pyrogenicity.

Detector features:

• Pulse height analysis;

• Uniformity;

• Spatial resolution and linearity;

• Energy resolution;

• Sensitivity;

• Count rate performance;

• Detector head shielding leakage.

Detector head motion.

Automatic patient–detector distance sensing.

Collision detection and emergency stops.

Collimators and collimator exchange mechanisms.

Imaging table and attachments.

Data acquisition features:

• General acquisition features;

• tatic acquisition;

• Dynamic acquisition;

• List mode acquisition;

• Gated cardiac acquisition;

• Whole body imaging;

• Tomography.

Data processing system:

• Data display;

• Image manipulation;

• Region of interest generation and display;

• Curve generation;

• Display and arithmetic;

• Processing of SPECT data;

• Quality control software

• Test data.

Accessories, such as features for physiological triggering, anatomical landmarking and phantoms.

Detector features:

• Spatial resolution;

• Sensitivity;

• Scatter fraction, count losses and random measurements;

• Energy resolution;

• Image quality and accuracy of attenuation, and scatter correction and quantitation;

• Coincidence timing resolution for time of flight PET accuracy.

Time of flight capability.

Data acquisition features, including 2-D and 3-D whole body imaging, and cardiac and respiratory gating.

Data processing system, including image reconstruction algorithms, image manipulation and image correction.

Emergency stop.

For preparation and dispensing of radiopharmaceuticals, working behind a lead glass bench shield, using shielded vials and syringes, and wearing disposable gloves;

During examinations, when the distance to the patient is short, using a movable transparent shield.

Shielded syringes should be utilized during the intravenous or intra-arterial administration of radiopharmaceuticals as necessary to ensure extremity doses are maintained below occupational dose constraints. Absorbent materials or pads should be placed underneath an injection or infusion site. The RPO at the facility should be consulted to determine the necessity of other protective equipment (e.g. shoe covers and step off pads) for particular radiopharmaceutical therapies.

For intravenous or intra-arterial administration by bolus injection, when dose rates warrant, the syringe should be placed within a syringe shield (usually a plastic shield for beta emitting radionuclides to minimize bremsstrahlung or a shield of high atomic number material for photon emitting radionuclides) with a transparent window to allow the material in the syringe to be seen. For intravenous administration by slower drip or infusion, the container containing the radioactive material should be placed within a suitable shield. For high energy photons, a significant thickness of lead or other high atomic number material may need to be used. In addition, consideration should be given to the shielding of pumps and lines.

For oral administration of therapeutic radiopharmaceuticals, the radioactive material should be placed in a shielded, spill-proof container. Care should be taken to minimize the chance of splashing liquid or of dropping capsules. Appropriate long handled tools should be utilized when handling unshielded radioactive materials.

Shields for bench tops, vials, syringes, activity meters and for the preparation of the radiopharmaceuticals (i.e. L-blocks and side blocks) of a material and thickness appropriate to the type and energy of the radiation. Particular considerations for the choice of shield include the following:

• Alpha emitters may need to be shielded by high atomic number materials because of their characteristic X rays and high energy gamma components.

• ²²³Ra does not need a high atomic number shield because the gamma component does not contribute significantly to the dose.

• Solutions containing pure low energy beta emitters, such as ¹⁴C, require a plastic shield to attenuate the beta particles.

• Solutions containing high energy beta emitters, such as ³²P and ⁹⁰Y, require a plastic shield to attenuate the beta particles followed by a high atomic number material shield for the bremsstrahlung radiation.

• Solutions containing radionuclides that have both beta radiation and gamma radiation, such as ¹⁶⁹Er, ¹⁷⁷Lu, ¹⁸⁶Re and ¹⁵³Sm, may need lead shielding to attenuate the high energy gamma photons.

• Gamma emitters always require shielding by high atomic number materials.

Protective clothing should be used in work areas where there is a likelihood of contamination, such as in areas for radiopharmaceutical preparation and administration. The protective clothing may include laboratory gowns, waterproof gloves (made of latex or non-latex material such as neoprene, polyvinyl chloride or nitrile), overshoes, and caps and masks for aseptic work. The clothing serves both to protect the body of the wearer and to help to prevent the transfer of contamination to other areas. The clothing should be monitored and removed before the wearer leaves a designated area. When moving between supervised areas such as the camera room and the injection area, the wearer might not need to change the protective clothing unless a spill is suspected. It is good practice to change gloves after each manipulation. Protective clothing should be removed before entering other areas, such as staff rooms.

When lower energy beta emitters are handled, gloves should be thick enough to protect against external beta radiation.

Lead aprons should be worn when entering a room with hybrid imaging (e.g. PET–CT) if the X rays are about to be used and either a carer or comforter or a staff member needs to be in the room with the patient. Lead aprons may also be worn when preparing and administering high activities of ^99mTc, although their use is not recommended, as other protective measures are more effective (see para. 4.83).

Tools for remote handling of radioactive material, including tongues and forceps.

Containers for the transport of radioactive waste and radioactive sources.

Fume hoods, fitted with appropriate filters and adequate ventilation, should be used with volatile radiopharmaceuticals, such as ¹³¹I and ¹³³Xe. The sterility of the intravenous or intra-arterial radiopharmaceuticals should be preserved.

All work surfaces (including the interior of enclosures), tools, equipment and devices (including dosimetry systems, computers and peripherals, and stress testing units), the floor and any items removed from these areas;

Workstations, ventilation systems and drains, when any of these needs to be accessed for maintenance purposes;

Protective and personal clothing, and shoes, particularly when the wearer is leaving a controlled area (monitors should be available near the exit);

Clothing, bedding and utensils used by radiopharmaceutical therapy patients.

A single dosimeter placed under the apron, reported in H_p(10), provides a good estimate of the contribution to the effective dose of the parts of the body protected by the apron, but underestimates the contribution of the unprotected parts of the body (the thyroid, the head and neck, and the extremities).

A single dosimeter worn outside the apron, reported in H_p(10), provides a significant overestimate of effective dose and should be corrected for the protection afforded by the apron by using an appropriate algorithm [120, 122].

Notwithstanding (a) and (b), in nuclear medicine, a single dosimeter under the apron provides an estimate of the effective dose that is sufficient for radiation protection purposes.

Has it already been done? A radiological procedure that has already been performed within a reasonable time period (depending on the procedure and clinical question) should not be repeated (unless the clinical scenario indicates the appropriateness of repeating the procedure). In some cases, an alternative procedure may have already been performed in another facility, making the proposed radiological procedure unnecessary, for example a patient who has recently undergone a CT pulmonary angiography in one facility might be referred for a ventilation/perfusion scan at another facility. The results (images and reports) of previous examinations should be made available, not only at a given nuclear medicine facility but also for consideration at different facilities. Digital imaging modalities and electronic networks should be used to facilitate this process.

Is it needed? The anticipated outcome of the proposed radiological procedure (positive or negative) should influence the patient’s management.

Is it needed now? The timing of the proposed radiological procedure in relation to the progression of the suspected disease and the possibilities for treatment should all be considered as a whole.

Is this the best investigation to answer the clinical question? Advances in imaging techniques are taking place continually, and the referring medical practitioner may need to discuss with the radiological medical practitioner what is currently available for a given problem.

Has the clinical problem been explained to the radiological medical practitioner? The medical context for the requested radiological procedure is crucial for ensuring the correct technique is performed with the correct focus.

Owing to the higher radiosensitivity of the embryo or fetus, it should be ascertained whether a female patient is pregnant before a nuclear medicine procedure is performed. Paragraph 3.176 of GSR Part 3 [3] requires that procedures be “in place for ascertaining the pregnancy status of a female patient of reproductive capacity before the performance of any radiological procedure that could result in a significant dose to the embryo or fetus”. Pregnancy would then be a factor in the justification process and might influence the timing of the proposed radiological procedure or a decision as to whether another approach to treatment is more appropriate. Care should be taken to ascertain that the examination or treatment selected is indeed indicated for a medical condition that requires prompt medical treatment. Confirmation of pregnancy could occur after the initial justification and before the radiological procedure is performed. Repeat justification is then necessary, with account taken of the additional sensitivity of the pregnant patient and embryo or fetus.

• (i) Most diagnostic procedures with ⁹⁹mTc do not cause high fetal doses. For radionuclides that do not cross the placenta, the fetal dose is derived from the radioactivity in maternal tissues. Some radiopharmaceuticals, or their breakdown components, that do cross the placenta and concentrate in a specific organ or tissue can pose a significant risk to the fetus. Particular attention should be given to radiopharmaceuticals labelled with iodine isotopes. Radiopharmaceuticals labelled with other radionuclides, in particular positron emitters, need special consideration. In all these instances, the medical physicist should estimate the fetal dose. Detailed information on doses to the embryo or fetus from intakes of radionuclides by the mother is given by the ICRP [234].

• (ii) As a rule, a pregnant patient should not be subject to radioiodine therapy unless the application is lifesaving. Otherwise, the therapeutic application should be deferred until after the pregnancy and after any period of breast-feeding [124, 235, 236]. In particular, radioiodine will easily cross the placenta, and the fetal thyroid begins to accumulate iodine at about ten weeks of gestation.

In breast-feeding patients, excretion through the milk and possibly enhanced dose to the breast should be considered in the justification process. Detailed information on doses to infants from the ingestion of radionuclides in breast milk is given by the ICRP [237].

As children are at greater risk of incurring radiation induced stochastic effects, paediatric examinations necessitate special consideration in the justification process [233].

There should be an effective system for correct identification of patients, with at least two, preferably three, forms of verification, for example name, date of birth, address and medical record number.

Patient details should be correctly recorded, such as age, sex, body mass, height, pregnancy and breast-feeding status, current medications and allergies.

The clinical history of the patient should be reviewed.

Appropriate selection of the best available radiopharmaceutical and its activity, with account taken of special requirements for children and for patients with impaired organ function.

Adherence to patient preparation requirements specific to the study to be performed. Examples include:

• Use of methods for blocking the uptake in organs not under study and for accelerated excretion, when applicable.

• Withdrawal of medications, food or substances that might interfere with the outcome of the procedure.

• Correct hydration.

The storage or retention of radiopharmaceuticals within specific organs can be influenced by drugs such as diuretics or gall bladder stimulants, whenever they do not adversely interfere with the procedure. This method is sometimes used to increase the specificity of the examination, but has also a positive influence on radiation protection, for example the use of a ‘diuretic challenge’ in renography.

For children undergoing diagnostic procedures, the amount of activity administered should be chosen by utilizing methodologies described in international or national guidelines [62, 204, 205, 209, 238, 241–243].

Use of appropriate image acquisition parameters:

• In nuclear medicine and with a gamma camera (planar and SPECT systems), this may include selection of the collimator, acquisition matrix, energy windows, acquisition zoom, time per frame and imaging distance.

• For PET systems, this may include 2-D and 3-D acquisitions, matrix size, field of view, time of flight, attenuation correction, slice overlap, scatter correction and coincidence timing.

Use of appropriate reconstruction parameters (e.g. algorithm, matrix, filters, scatter correction and zoom factor), and application of appropriate image corrections (e.g. attenuation and scatter correction, and, in the case of PET systems, random correction).

Utilization of quantitative and qualitative capabilities, such as the generation of region of interest analysis, time–activity curve generation, image reformatting, or tissue uptake ratios, specific to the clinical need.

Verbal and written information and instructions should be provided to patients about their radiopharmaceutical therapy and about how to minimize exposure of family members and the public, and advice should be provided on pregnancy and contraception after therapy (for detailed guidance, including sample information sheets, see Refs [21, 204, 246–249]).

Special attention should be given to preventing the spread of contamination due to patient vomit and excreta.

A protocol should be drawn up for the release of patients after the administration of therapeutic doses of radiopharmaceuticals (see the guidance in paras 4.246–4.248).

A protocol should be drawn up for the actions to be taken when the dose incurred is above or below the value prescribed by the radiological medical practitioner as required by para. 3.180 of GSR Part 3 [3].

The dose on the radiopharmaceutical label matches the prescription;

The identity of the patient by two independent means;

The identity of the radionuclide;

The identity of the radiopharmaceutical;

The total activity;

The date and time of calibration.