Thematic Safety Areas: Medical Exposure Control

The delicate balance behind patient health and safety

Medical procedures constitute the single largest means through which people encounter exposure from man-made radiation sources. In fact, more than 95% of human exposure to man-made ionizing radiation results from diagnostic and interventional radiology. The other main source is radiotherapy, which is prescribed for a much smaller proportion of the population but carries different, and more serious, risks of accidental exposure.

As defined by the Basic Security Standards, standards for radiation exposure control in medical settings extends to the patient, any comforters present (relatives or friends accompanying the patient), and volunteers exposed during biomedical research. Medical personnel are covered under standards related to occupational exposure control. As in the case of occupational settings, responsibility for exposure control lies with the licensee but the power to grant, suspend or revoke licenses is held by the national regulatory authority.

There is, however, one distinction. In medical settings, the licensee further assigns the primary task and obligation of ensuring overall patient protection and safety to the medical practitioner(s) who makes decisions about the prescription and delivery of medical
exposure.

In radiological diagnosis, radiation is used to create images of internal body tissues and organs. Typical tools include radiology (X-rays, mammography, computed tomography, etc.), all of which use a radiation source outside the body, and nuclear medicine, in which radioactive substances (called radiopharmaceuticals or radiotracers) are injected or ingested. The goal of either approach is to obtain an image that provides sufficient information to support accurate diagnosis.

A related area, which is growing rapidly, is interventional radiology. In these procedures, medical practitioners use real-time images to guide minimally invasive techniques for diagnosis and treatment — often as an alternative to surgery. In terms of radiation protection in radiology, the emphasis is on finding ways to minimize exposure without losing vital information from the resulting image. One of the challenges is finding the right balance: it is not always necessary to achieve an image of extremely high quality —just one that contains enough information. Thus, a lower dose of radiation is often sufficient for the task at hand.

To grasp the importance of medical exposure, it is useful to compare patient exposure rates to those typical of employees in occupational settings. The exposure a patient receives from one single computed tomography examination is similar to what the attending radiologist would receive in 10 to 20 years of working in a radiology department. It is estimated that diagnostic medical exposure to the population is approximately 150 times higher than occupational exposure. This is one of the reasons for placing such strong emphasis on optimizing procedures: achieving an exposure reduction of even 1% in medical exposure would be like eliminating occupational exposure altogether.

Various opportunities to optimize protection have already been identified. Recent surveys reveal large differences in doses amongst radiology departments, indicating an untapped potential for dose reduction. There is also evidence to suggest that cardiologists and medical practitioners who have not been trained in radiation use very large amounts of radiation for interventional procedures. Use of digital radiology is increasing dramatically, but its simplicity may also lead to excessive exposure. Studies have shown that, in some cases, satisfactory images can be obtained with one-tenth of the dose being used.
In radiotherapy, the objective is very straightforward: deliver the right dose of radiation to kill the right cells – those that have formed a tumor. Too little radiation is ineffective; inaccurate aim can kill off healthy tissue and leave cancerous cells to continue multiplying. On the other hand, unnecessarily high doses can cause damage to surrounding normal tissue or organs. In this area of medical radiation, reducing accidental exposure is the top priority for safety.

The IAEA believes that training (through workshops, fellowships, etc.) a broader range of health professionals on protection issues related to radiology, nuclear medicine and radiotherapy is one of the most effective means of achieving patient protection. Scientific conferences also provide an excellent opportunity for information sharing and networking. This was evidenced in March 2001 (Málaga, Spain), when the IAEA joined forces with the European Commission, the Pan-American Health Organization and the World Health Organization to sponsor an international conference entitled Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiotherapy.

Efforts to optimize protection to reduce unnecessary exposure and accidents are particularly timely. It is expected that medical exposure will increase steeply in the coming years as new technologies are developed and existing technologies are used more extensively. In fact, there is an urgent need to bring even the most basic tools (imaging diagnosis and radiotherapy) into developing countries to reduce morbidity and mortality to diseases that are now considered quite manageable in developed nations.