New technologies, new risks

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ICRP Publication 86, ‘Prevention of accidental exposures to patients undergoing radiation therapy’, was published in 2000 (ICRP, 2000). The usual life span of the ICRP recommendations exceeds, sometimes by far, a full decade. Consequently, it may appear somewhat surprising to see ICRP publishing a new document focusing on the risks of accidents in radiotherapy less than 10 years after ICRP Publication 86.

In fact, the authors of ICRP Publication 86 had somehow anticipated such a need: a few sentences found in the text appear to foreshadow this publication. A full section (5.9) was devoted to ‘The potential for accidental exposures in the future’. What was written in this section deserves to be repeated here:

‘The recommendations…[in this publication] are based on a retrospective analysis of accidental exposures in radiation therapy with past and current types of equipment. There are, however, a number of factors that may cause a change in this picture in the future:

–With the worldwide expansion of radiotherapy there may be more accidents related to inadequate staff training….

–…Accidents may occur due to inadequate accelerator maintenance…. The increased number of computer-controlled systems may also lead to more computer related accidents, compared to mechanical failures.

Moreover, the Summary of ICRP Publication 86 notes that ‘Major accidental exposures are rare, but it is likely that they will continue to happen unless awareness is increased. Accidents will usually occur as the result of inadequate education and training, lack of quality assurance, poor infrastructure, equipment failure, and improper decommissioning. Unless these issues are properly addressed and dealt with, more accidental exposures are likely to occur, as current and new technologies developments are disseminated.’

Actually, the authors of ICRP Publication 86 would clearly have preferred to be wrong! Unfortunately, they were not and it has recently become apparent that their pessimistic predictions were partly right.

Obviously, ICRP acknowledges the impressive recent technological developments of modern radiotherapy, primarily ‘conformal’ radiotherapy and IMRT. It must be recognised that these developments brought new and unmatched precision to radiation oncologists. This precision allows both a reduction in the volume of healthy tissue that has to be irradiated (with a consequential reduction in side effects and complications), and a dose escalation to the tumour, which has already proven in some instances (e.g. prostate cancer) to increase the cure rate significantly.

Unfortunately, the dark side of these successes is that the new and more sophisticated technologies give rise to new types of accidents. Let us take a single, simple example. With so-called ‘conventional’ or ‘classical’ radiotherapy (on which ICRP Publication 86 was primarily based), all data for the treatment of a given patient had to be re-entered for each of the fractions. In this setting, ICRP Publication 86 noted that, for an entire treatment, approximately 1000 parameters (!) had to be entered manually. This obviously led to a non-negligible risk of human error. However, it has to be emphasised that the errors generally occurred for no more than a few fractions, and usually did not lead to significant ‘over’ or ‘under’ doses. In other words, the conventional procedures most probably led to a significant number of errors, but usually with limited deviations from the prescribed total dose, and therefore without serious consequences for the patients.

With the general introduction of computers in radiotherapy, things have changed. Today, all data are registered from the beginning and ‘recalled’ automatically for each fraction. On one hand, this avoids the risk of deviations due to multiple data re-entries. On the other hand if, unfortunately, some error arises during the initial data entry, it may impact on the entire treatment, with dose deviations which are generally much larger than before. In summary, the new techniques result in far fewer errors, but such errors, when they do occur, can be much more severe.

Moreover, new types of accidents have been encountered due to: the complexity of the present treatment preparations; the increased sophistication of the whole treatment process (with an increasing number of steps and more people involved); the omnipresence of computers with frequent and regular upgrading of more and more complicated software; and the difficulty of regularly and correctly training all the physicians, physicists, dosimetrists, engineers, etc. involved in a busy radiotherapy unit.

Such accidents have been honestly recorded and analysed in various countries. They have been responsible for complications of varying severity, including the deaths of patients in some instances.

ICRP could not ignore or dismiss this reality, so the decision was made to develop a new document dealing with these new risks in modern radiotherapy. Pedro Ortiz López, who had been the Chair of the ICRP Task Group that wrote ICRP Publication 86, agreed to form a new Task Group. The role of this new Task Group was to propose new recommendations for the prevention of accidents in radiotherapy, taking into account the changes and the more recent developments of the last decade.

These new recommendations are based on: lessons learned through experience; the continuous control of computer software; regular control of the ballistics; precise checking of the delivered dose (in particular, by in-vivo dosimetry); and more. As such, it is the hope of this Task Group, Committee 3, and ICRP as a whole that these new recommendations will help to reduce the risk of accidents in modern radiotherapy significantly, both in terms of frequency and severity.

The ultimate goal is to be able to offer cancer patients the more recent and sophisticated modern radiotherapy techniques, which are expected to be more efficient and with less chance of side effects, in safer conditions.

Jean-Marc Cosset

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Reference 

1. ICRP . Prevention of accidental exposures to patients undergoing radiation therapy. ICRP Publication 86. Ann. ICRP. 2000;30(3):
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