The three principles of radiation protection; justification, optimisation and dose limitation, were established by ICRP almost 50 years ago. The principle of justification originally arose from radiation protection considerations in the medical field, where it was assumed that all medical exposures would be clinically justified. Indeed, within medical practice it is generally assumed that all interventions and not just those involving the use of ionising radiation should be clinically justified. Thus, by generalising the principle of justification to all practices involving the use of ionising radiation, ICRP has created an anomalous situation.
Clinical justification operates at the level of the individual patient and is a fundamental component of medical ethics. However, justification within the framework of radiation protection operates at the level of a particular practice. Although, if a practice is justified considerations of justification at the individual patient level may then apply. Hence, which level of justification takes precedence? Although this might appear to be an academic exercise when a period of technological stability exists, it is relevant when new or modified applications of ionising radiation enter the clinical field, which has occurred over the past 40 years.
When a significant growth in the development of new or updated medical techniques occurs the illogicality of the concept of justification in radiation protection is highlighted. In fact, the rigid application of this principle at the practice level would severely limit the development of new and exciting clinical applications of ionising radiation. In reality, justification of radiation practices in the medical field can only sensibly operate on the basis of clinical justification. This is clearly demonstrated when considering the introduction and development of new and/or modified clinical applications employing ionising radiation. Recent examples concern the use of protons in external beam therapy and Artificial Intelligence applications in diagnostic radiology.
Can justification of practices ever precede the application and testing required to ensure that clinical benefit is gained. The rationale for such testing is that a new technique could introduce improvements in therapy or diagnosis based upon strong scientific or clinical indications. Consequently, there are justifiable reasons for pursuing a clinical evaluation programme of a practice so that it is the reasons for this action that are justified and not the practice. Only following a rigorous evaluation process may the practice be eventually and demonstrably justified.
It is interesting to note that a period of evaluation may also be accompanied by developments in the technique itself through modification of protocols or the introduction of new technology. In the case of therapeutic applications this may improve the clinical outcome, the treatment delivery process as well as optimise the dose delivered. For diagnostic applications this may improve the image quality, overall information gained and may or may not reduce the patient dose. The development of CT is an example of a development that significantly increased both individual as well as population doses but also significantly increased clinical information. Thus, under such circumstances, optimisation does not necessarily follow justification of a practice but may in fact precede it.
An important demonstration of the principle of clinical justification superseding justification of practices occurred in the field of breast screening. There was strong evidence that the widespread application of a breast screening programme that met certain quality standards, could save lives. However, it was necessary to establish large scale programmes accompanied by the analysis of results obtained over a period of time to demonstrate the clinical benefits expressed in terms of years of life saved.(1)
Over the course of a number of years the dose required for an image as well as the image quality has improved significantly. The use of vacuum-packed industrial film that occurred in the early days of breast imaging, with concomitant high doses, could not now be justified. Thus, it was the justification of the reason for pursuing a breast screening programme and not the programme itself that drove clinical practice. Incidentally, the success of breast screening programmes has now introduced the problem of over diagnosis, whereby cancers are detected that would not necessarily lead to an individual’s death. Hence, individuals may receive an intervention that might not be necessary. However, screening programmes generally fall under a public health umbrella so that the benefits to a population rather than specific individuals becomes the primary consideration.
The introduction of proton therapy into the clinical domain demonstrates the justification of the reasons for pursuing investigations into the efficacy of this form of treatment, but not necessarily justification of the practice itself. There are still many problems to overcome and areas where technological developments are desirable.(2,3,4) Nonetheless, it is felt that the potential benefits of this type of therapy are sufficiently great to merit its application, evaluation and technological development. However, it has been pointed out that, “Another concern about proton therapy has been its high cost.”(2) Consequently, consideration of all relevant factors that underpin the justification for the routine clinical implementation of proton therapy will require the application of cost-risk -benefit analysis(5).
The application of Artificial Intelligence (AI) in diagnostic radiology could affect the efficacy of an examination. This might impact the clinical justification of undertaking an examination if the performance in terms of specificity and sensitivity was lowered. Since the introduction of AI to report images will be applied in parallel with existing human-based reporting, at least in the developmental stages, clinical justification, again will be the driving force for its application. Given the significant growth in radiological examinations worldwide and the concomitant costs associated with manpower training and reporting, effective support tools for interpreting clinical information and standardising outputs will be desirable. This can help to level up healthcare quality worldwide and the cost element of any cost-risk-benefit analysis will be a major driver for change. Any radiation protection considerations will be of secondary importance. In many parts of the world, merely having access to diagnostic radiology services will take precedence over any patient dose considerations.
AI techniques are also being applied in the reconstruction of CT data to try and reduce the number of projections needed to produce anatomical cross sections without a loss of image quality. This has the potential to reduce the dose to the patient. However, a potential advantage would be to employ the dose saving produced on a conventional scan protocol to the application of dual energy techniques. Thus, scans would be undertaken at more than one beam quality and the overall dose to the patient would not be altered or may even increase. Clinical optimisation would be the driving force. This could require the application of pulsed generators that can switch between kV values and methods for switching kV’s from an X-ray generator quickly already exist. Alternatively dual filtration techniques can be applied in order to create images at more than one beam quality. Consequently, optimisation would be an inherent part of any development process, which would be driven by a desire for improved clinical performance.
Radiation protection in medical practices is patient centric and does not appear to fit into the ICRP framework implied by the three principles of justification, optimisation and dose limitation. The principles of radiation protection might be relevant to activities where persons at risk (workers, general-public) can be separated from the sources of ionising radiation. However, for the direct exposure of patients, clinical justification, as distinct from justification of practices, would appear to be the primary consideration that underlies all possible patient exposures.
Dr Mike Moores, Director