Process

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1. Introduction
2. Justification
3. Optimization
4. Optimization in children (Optimization in paediatric radiology)
5. Fetal optimization
6. Assessing patient radiation risk
7. Radiation protection of patients
8. Radiation protection of staff and public
9. Prevention of incidents

Introduction

Diagnostic radiology involves the use of X rays to produce morphological or functional images of the human body, based on the attenuation properties of X rays in the various tissues.

Like all practices dealing with potential exposures of humans to ionizing radiation, medical exposures in diagnostic radiology must be subject to the principles of justification and optimization of radiological protection. Justification of medical exposures requires that all medical imaging exposures must show a sufficient net benefit when balanced against possible detriment that the examination might cause. In addition to the requirements of optimization of radiological protection, the concept of optimization of clinical practice in diagnostic radiology must also be considered. This is the process requiring a diagnostic outcome for a patient from an imaging procedure while minimizing the factors that cause patient detriment.

Medical physicists are an important component of the team working in diagnostic radiology facilities, with responsibilities in the optimization of the dose and image quality in medical imaging. They work together with radiological medical practitioners, i.e., radiologists and medical radiological technologists, to interpret and optimize the technical aspects of the different methods of image acquisition and display. Medical physicists have responsibilities for the radiation safety and protection of patients, staff members and the public, related to the use of X rays in diagnostic radiology. Furthermore, the performance of X ray systems is fundamental in providing a safe and qualified service.

In the context of radiation protection, specific consideration is needed for sensitive population groups, e.g., children and females of reproductive age in the case of high dose examinations and in the use of radiological procedures involving asymptomatic individuals, e.g. as part of a health screening programmes.   

Justification

Justification in medical uses of ionizing radiation involves consideration of all three categories of exposure: medical, occupational and public exposure. According to International Basic Safety Standard, this principle of radiation protection is implemented more effectively as part of the medical process of determining the appropriateness of a radiological procedure. A medical exposure is justified if it provides a benefit to the patient in terms of relevant diagnostic information and a potential therapeutic result that exceeds the detriment caused by the examination. Imaging methods with lower patient dose should be considered if the same diagnostic information can be obtained. This is true for all patients but is especially important for younger patients. Furthermore, no new imaging modality should be established unless the exposed individual or society receives a net benefit to offset the detriment.

Justification of medical exposures is the responsibility of both the radiological medical practitioner and the referring physician. Its implementation requires three-level approach. At the first level, the general justification of medical exposures is the view that the use of radiation for medical purposes does more good than harm. At the second level, generic justification is carried out by the health authority in conjunction with appropriate professional bodies, considering current and new techniques and technologies as they develop as well as the application of the radiological procedure to a particular person. Justification of health screening programmes and screening intended for the early detection of disease, outside the health screening programme, are addressed at this level.  Finally, the third level of justification concerns an individual patient. population groups requiring special consideration with respect to justification are pregnant and paediatric patients.

Referral guidelines for imaging are assisting clinicians in making decisions on appropriate type of radiological examination, given the clinical conditions. Guidelines are important, since in certain instances, medical imaging examinations may not contribute to the management of the patient, and thus may add unnecessary radiation dose. The relevant examples are: repeated examination when relevant information was available but not obtained or when inadequate clinical information is obtained, preventing important clinical questions from being answered. Review of the justification may need to take place if relevant circumstances are changed.

Optimization

Optimization of medical imaging procedures is a fundamental requirement of quality practices and a key requirement of the International Basic Safety Standards. It is one of two radiation protection principles applied to medical exposure. It should be considered as a prospective and iterative process which requires limiting the exposure of patients to the minimum necessary to achieve the required diagnostic or interventional objective. The optimization of clinical practice is the process requiring a desired outcome for a patient from an imaging procedure while minimizing the factors that cause patient detriment.

Optimization is a multidisciplinary task that starts with an assessment of image quality and radiation dose throughout the department.  Specific steps for a successful optimization process are:

1. Establishment of a quality assurance programme;
2. Establishment of an optimization team consisting at a minimum of a radiologist, a medical physicists and medical radiation technologist. Each of these professionals has a unique role in the optimization process. The radiologist provides feedback on whether sufficient task-specific image quality is maintained, the medical physicist optimizes the exam protocol, and the radiation technologist ensures that the modified (optimized) exam protocol is feasible in the clinical workflow and executed correctly. At larger or more resourced institutions, the optimization team can include also an engineer and members of the department management;
3. Determination of baseline dose levels and image quality as well as comparisons with benchmarks to decide which exam protocols should be optimized;
4. Modification of protocols by the medical physicist. and the physicist should take a proactive lead in the everyday clinical routine in order to promote the value of optimization process;
5. Regular review of patient dose and image quality. After implementation, the optimization process should be repeated to determine effectiveness.

Medical physicists in diagnostic radiology provide a key contribution to the optimization of X ray imaging procedures, e.g. in the balancing the image quality and radiation dose. They are responsible for the dosimetry of the patient, assist medical practitioners in the evaluation of examination efficacy and participate in image quality and perception studies. Their knowledge is applied to the development and optimization of new imaging techniques, and they play an important role in the adoption, development, implementation and safe use of advanced techniques in diagnostic radiology.

Optimization in children (Optimization in paediatric radiology)

Radiation protection considerations in paediatric radiology are more critical than adults since children are more sensitive to radiation, due their rapidly dividing cells. In addition, paediatric patients have a long life expectancy thereby extending the time for radiation induced cancers to be expressed. Peadiatric patients often have multiple examinations, particularly in their early years of life.  Consequently, radiation doses to children should be closely monitored and examinations should be specially optimized. In addition, the organ doses may be proportionally higher than for larger patients because of the smaller body size.

The relationship between the examination protocol and the associated image quality and patient dose is dependent on the size of the patient. It is, therefore, important to adjust the exposure setting to the size of the patient, with involvement of a medical physicist and the responsible medical practitioner.

Special consideration needs to be given to the optimization process in computed tomography (CT). The CT protocol should be optimized, e.g.  by adjusting exposure parameters and careful selection of the slice width and pitch, as well as the extent of the scanning area.

Monitoring of patient radiation exposure provides relevant information for the optimization process, which is, in principle, similar for adult and paediatric patients. It is, however, important to note that dosimetry is more complex for paediatric patients due to the size range of patients, e.g., from a few kg to 100 kg or more. Paediatric patients are often grouped by age or weight. These groupings facilitate dosimetry studies consisting of a large number of patients.  However, this introduces increased uncertainty into the dose estimations.

The methodology for optimization is, in principle, a straightforward process leading to the identification of key points that require close attention to achieve successful practical outcomes in optimization. It has been successfully used in interventions to optimize dose and image quality in paediatric radiology:

1. Inclusion – involve medical physicist, radiographer and radiologist. Seek external expertise and advice if unsure;
2. Calibration – check accuracy and tolerance of displayed dose parameters;
3. Recording and archiving data for later review – initially keep exactly as displayed or downloaded;
4. Data accuracy – check at each stage of automated data transfer, in case of manual transcription of data – get it independently checked;
5. Unit conversion/calibration coefficients – get them independently checked;
6. Comparison of data – consider uncertainties;
7. Evaluate image quality – encourage clinicians to participate and use an appropriate image quality evaluation;
8. Interventions – ensure clinical acceptability via phantom tests and/or gradual introduction
9. Implementation – provide training to clinical staff & ensure this step occurs;
10. Results – share with all involved staff.

Fetal optimization

Patients who are pregnant should also be given particular consideration with respect to justification and optimization. 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 is performed, in particular for relatively high dose examinations involving exposure of abdomen or pelvis (e.g., CT of the lower abdomen, urography, colon and interventional procedures in that region).  Routine diagnostic CT examinations of the pelvic region can lead to a dose of 50 mSv to the fetus in early pregnancy.  The radiology facility should establish a procedure for ensuring the pregnancy status of patients.

For planed examination is pregnancy, methods to minimize the dose to the fetus should be developed and may, for example, include reduced the number of projections, use of technical parameters resulting in lower dose or collimation of the primary radiation beam. The medical physicist must provide recommendations on methods for the minimization of the dose to the foetus. 

If the fetus is exposed during either a planned or accidental medical exposure, for example trauma CT of an unconscious pregnant woman, the medical physicist should be contacted to estimate the foetal dose and provide guidance regarding the risk to the foetus, in order for the clinician to inform the woman of the risks involved.

The first issue in estimating foetal dose is determination of the number of X ray examinations and projections, and the location of the foetus relative to the X ray beam. This can be accomplished by reviewing the images.  Next, one must estimate the entrance dose to the patient based on information for digital images or records which may be available with exposure parameters. This information is then used to estimate the foetal dose using software or tables available in the literature. The medical physicist must provide estimates of the risk of the radiation dose to the foetus, depending on foetal age. The risk should be considered in the context of risk of naturally occurring birth complications and defects, as well as other risk factors.

Assessing patient radiation risk

The risks associated with diagnostic radiology examination vary significantly, depending on the radiological procedure. At the low risk end are dental exposures and bone densitometry studies, whereas commuted tomography and interventional procedures are at the high risk end.  Risk-benefit consideration are implicit in the applying justification and optimization principles.

Most concern in diagnostic radiology is focused on stochastic risk. The effective dose provides a limited method to estimate the stochastic risk, but the uncertainties in this estimate must be appreciated and communicated. The limitations of the effective dose for use in diagnostic radiology patient doses must be understood, including the variability of risk with age, dose rate, etc. Other important topics include absolute versus relative risks, typical doses and risks from medical exposures, and the contribution of population collective dose from medical exposures.

Deterministic effects, though limited in diagnostic radiology, are important since they can produce significant morbidity in patients undergoing interventional procedures. 

Certain population groups of people require special consideration in terms of risk-benefit analysis, including: patients who are or might be pregnant, paediatric patients, individuals subject to medical exposure as part of health screening programme and volunteers in biomedical reach.   

The medical physicist must be able to assess the radiation risk to both patients and staff in diagnostic radiology. The medical physicist must also have an appreciation of the benefits of diagnostic radiology procedures and be able to compare these benefits and risks to other risks, e.g., the risks and benefits of radiation from an abdominal CT examination to the risks of morbidity and mortality from abdominal surgery. In order to do this an understanding of radiobiology and epidemiology, dosimetry, and audit techniques is required. The medical physicist must also be able to provide advice on these risks to staff and patients, and on strategies for radiation risk reduction.

Radiation protection of patients

As per United Nations Scientific Committee on Effects of Atomic Radiation (UNSCEAR) 2020/2021 Report, medical exposure remains by far the largest man-made source of radiation exposure of the population. In the period 2009–2018, about 4.2 billion medical radiological examinations were performed annually. The collective effective dose was estimated to be 4.2 million man sieverts (man Sv), resulting in an effective dose per caput of 0.57 mSv. Computed tomography makes the largest contribution (about 62%) to the collective effective dose but accounts for only about 10 % of all procedures. Furthermore, the total number of computed tomography examinations has increased by about 80 %, and its contribution to the collective effective dose has increased from 37 % to 62 %.

With respect to associated radiation risks, an international framework to ensure a better understanding of radiation protection requirements and improve safety of patients has been established. Relevant health professionals should be made aware of their responsibilities on the overall patient protection and safety in the prescription and delivery of medical exposure. Justification and optimization are two of the cornerstones of radiation protection in medical exposures, as dose limits do not apply to medical exposure.

As per International Basic Safety Standards, all diagnostic X ray examinations shall be justified in terms of clinical benefits and associated radiation risks and examination shall be performed only if benefit outweighs the risk. Once justified, examination should be performed in a way that provides required diagnostic information with minimal possible dose to patient. Although there are some common principles of protection that apply to all X ray imaging procedures, many of the most significant issues and actions are related to the specific modality used. The use of justification and optimization is most important in high dose procedures and computed tomography and interventional procedures and for special population groups as children and female patients of reproductive capacity.

In diagnostic radiology departments, medical physicists have responsibilities for the radiation safety and protection of patients, staff members and the public, related to the use of ionizing radiation.  Medical physicists have responsibilities in the development and implementation of a clinical radiation safety programme for the radiation protection of patients in areas where diagnostic radiology equipment is used.

Radiation protection of staff and public

The medical use of X rays in diagnostic and interventional radiology remains a rapidly changing field with a wide range of applications, procedures and techniques. The field has the largest single group of workers, including radiologists and other clinicians, medical physicists, radiographers and nurses, occupationally exposed to artificial sources of radiation..  Members of the public also need to be protected against radiation while in a radiological facility.

The extent of occupational exposure of workers in radiological facilities depends on the type and complexity of the procedures employed, typically involving: interventional radiology, general radiography, computed tomography, fluoroscopy, mammography, and dentistry. For procedures with fixed installations, the staff members are generally adequately protected by well-designed shielding barriers and their occupational exposure is not significant. However, workers in close proximity to the patient, for example physicians involved in fluoroscopy including interventional procedures, may be subject to considerable radiation dose. In these situations, staff dose levels during their working life can in some cases lead to the occurrence of deterministic effects such as cataract damage, if radiation protection actions are not utilised. 

The principles of the protection of workers from ionising radiation in all areas of medicine are directed at the prevention of deterministic effects and minimization of risk for stochastic effects (cancer). These principles include the use of dose limits for workers and general public.

The control of occupational exposure in diagnostic and interventional radiology is effectively utilised by: (i) design of facilities and imaging equipment including the, designation of workplaces as controlled and supervised areas, (ii) individual monitoring, (iii) use of personal protective devices (lead lined aprons, leaded glass eyewear, thyroid shields, protective screens, etc.) (iv) reduction of the time when the worker is exposed to radiation and (v) by moving as far away from the source of radiation while still doing the required work actions. Essential for all these activities is education and training which is a prerequisite for the establishment of safe working procedures. There are many common factors that affect both patient and staff doses. It should be remembered that every action to reduce patient dose will also reduce staff dose, but the reverse is not true.

Public access to designated areas in hospitals and radiology rooms is restricted. Therefore, radiation protection of the public will be efficiently achieved by necessary shielding and by safe working procedures that avoid directing of X ray tube towards areas with public occupancy.

Dose limits are introduced to ensure the occupational exposure of any worker is controlled and below a certain dose per time period, as outlined in the International Basic Safety Standards. The sources of exposure of the general public are primarily the same as for workers. However, based on the level of acceptable risk, different dose limits apply to members of the public and workers.

In a number of situations, particularly in those involving children, the examinations can be better performed with the assistance of a carer or comforter, for example a relative in the case of a paediatric patient, or a relative or friend for a disabled or very elderly or very ill patient. In these situations the comforter will be exposed, usually to a low dose, but not as a member of public. Therefore, the public dose limits do not apply to him/her. The radiation protection of the carer or comforter should be optimized, and, as part of this process, dose constraints apply.

Prevention of incidents

When considering risks in diagnostic and interventional procedures in diagnostic radiology, it should always be remembered that the patient is gaining a major potential benefit from both diagnostic and interventional procedures. Unintended incidents do, however, occur. In order to prevent incidents in diagnostic and interventional procedures, it is necessary to learn from those that have occurred in the past. In interventional procedures, possible incidents would mainly include inadvertent exposure of fetus, skin injuries in patients and eye lens injuries in staff involved in interventional procedures.

Inadvertent fetal exposure can arise, e.g., when a pregnant patient is unaware that she is pregnant. Following such an event an investigation should be carried out as per established procedure and the patient should be counselled.

Radiation induced skin injuries happen very rarely with an estimated frequency of about one in 10,000 interventional procedures, with a large margin as many injuries go unreported. The skin injuries can vary from mild erythema to deep skin ulceration. Review of the circumstances of many of the skin injuries reveals a lack of knowledge by the physicians performing these procedures of the biological effects associated with radiation. However, such injuries are rare events and can, in most situations, be avoided if adequate quality assurance programme is in place, e.g., if the personnel are adequately trained and the imaging system is subject of the quality control programme.

Occupational exposure in medicine is one of the areas in which increased eye lens exposure is likely to occur, particularly in fluoroscopy guided procedures in radiology and cardiology. Other areas include orthopedic surgery, urology, anesthesiology, vascular surgery, CT fluoroscopy and gastroenterology. However,  eye lens dose monitoring and radiation protection tools, most importantly protective screens or lead glasses, the risk for eye injuries is controlled. The protective tools are advised for staff performing interventional procedures in radiology and cardiology, as well as for personnel using fluoroscopy outside imaging departments. Furthermore, if X ray equipment is properly maintained and used, one can keep the radiation dose to eye lens at the minimal level.

Medical physicists are responsible for performing risk assessments and identifying possible radiation emergencies, such as incidents resulting from equipment malfunction or human errors. Medical physicists should develop action procedures to be followed in the event of such occurrences and carry out drills to verify that procedures can be carried out correctly. The physicists should also participate in the investigation of incidents involving radiation and provide the appropriate report and documentation.