Patient exposure to ionising radiation is differentiated from the other types of exposure (workers, population) because it is not subject to any strict limitations. Nonetheless, the justification and optimisation principles still apply. This is also the only case in which exposure is delivered for the direct benefit of the exposed persons, i.e. the patients. The worker and the population exposure consequences of the use of ionising radiation for medical purposes are mentioned in section 5 of this chapter.

The situation differs according to whether one considers patient exposure in the course of diagnostic applications (diagnostic radiology or nuclear medicine) or of external or internal radiotherapy: in the first case, optimisation is required, by delivering the minimum dose needed to obtain pertinent diagnostic information, while in the second, the dose needed to sterilise the tumour must be delivered, while preserving as much of the surrounding sound tissue as possible.

The dose received by the patient depends on the quality of the equipment used, what fully justifies retiring obsolete equipment and developing a quality control system for the medical appliances used. This concerns not only the irradiating equipment, but also those used for this exposure (if a radiological film viewer is defective, this could lead to increase the radiation doses to produce the films). The dose also depends on the nature of the procedures and the emission of radiation (X-ray tube, particle accelerator, unsealed source of radionuclides, etc.).

At present it is hard to gain a precise picture of overall exposure of medical origin, because the number of examinations carried out (per type) is still inadequately known and the doses delivered for the same examination may vary widely, depending not only on the performance conditions but also on the morphology of the patients. This is why, through its Action Plan for monitoring patient exposure to ionising radiation - PASEPRI (see chapter 1, point 3.4) the ASN has initiated a process to collect these data, with the assistance of the IRSN and the InVS. These 2 organisations therefore set up a survey unit with the purpose of collecting and analysing data. The work carried out was first of all to identify the various available sources of information, to update the available data on the volume and nature of the radiological examinations and to initiate targeted studies of scanners, neuroradiology and paediatric radiology.

Based on the initial results available after a year of operation of the survey unit, the number of radiological examinations carried out in France every year is somewhere between 61 and 74 million procedures, broken down as follows:
• 90% of the examinations made involve conventional radiology techniques;
• About 8% of examinations involve tomography;
• Nuclear medicine and surgical radiology each account for between 1 and 1.5% of the total number of examinations.

Starting from these data, the IRSN and InVS estimate that the average annual effective dose due to medical exposure per inhabitant in France, is somewhere between 0.66 and 0.83 mSv. Morover, although conventional radiology accounts for 90% of the examinations conducted, its contribution to the annual effective dose is only 35%. Conversely, tomography examinations, which only represent 8% of the number of examinations carried out, account for 41% of the annual effective dose, while surgical radiology (less than 1.5% of examinations) represents 15%.

Worldwide statistics, which need to be updated - (UNSCEAR 2000 report, volume 1) covering 1.530 billion inhabitants (1991-1996 data), indicate an annual effective dose per inhabitant of 1.2 mSv for radiology, 0.01 mSv for odontology and 0.08 mSv for nuclear medicine. In western Europe, for diagnostic radiology, the average annual effective dose per inhabitant is 0.33 mSv in the United Kingdom and 1.9 mSv in Germany.