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Editorial |
1 Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne NE4 6BE, 2 Medical Physics Department, Cookridge Hospital, Leeds, UK
Correspondence: Roger Harrison, Honorary Editor (Scientific), British Journal of Radiology, Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne NE4 6BE, UK. E-mail: r.m.harrison{at}ncl.ac.uk
In vivo dosimetry (IVD) in radiotherapy uses externally applied dosemeters to measure doses on the surface of patients whilst they are receiving treatment. These measurements can be related to the prescribed dose and can thus be used to check that the correct dose has been delivered.
As part of his 2006 report, the Chief Medical Officer, Sir Liam Donaldson, recommends that IVD is made routine [1]. Upon initial reflection, the introduction of a technique that would improve patient safety by providing a check of the delivered dose seems to be a valuable objective and one which would attract the support of all those involved with radiotherapy delivery. IVD equipment has been widely available for over 20 years, and radiotherapy service providers have long been aware of its potential to discover treatment delivery errors. However, at this time in the UK, the use of IVD as a treatment verification tool is not widely implemented, with most centres reserving its application for specialized techniques such as total body irradiation.
Given the apparent potential of IVD to detect treatment errors, it may not be obvious why IVD is not already in routine use throughout the country. There are three parts to the answer — time, cost and effectiveness.
Establishing and maintaining an IVD service is an extremely labour-intensive exercise and the Chief Medical Officer's report is not explicit about the nature and scope of IVD to be performed. Nevertheless, we can imagine that, if more widespread IVD programmes are unfunded, daily dosemeter positioning during treatment, interpretation of the results and any subsequent action might result in longer treatment times, reduced treatment throughput and hence added pressure on waiting-time targets. We might also imagine that the unfunded development and maintenance of such a service might divert resources from the development of techniques (e.g. intensity modulated and image-guided radiotherapy) that are designed to improve treatment outcome.
In principle, implementation of IVD nationwide could be achieved without such detriment if sufficient additional funding were available. However, the radiotherapy community also needs to address the question of whether IVD is likely to be an effective use of resources in the drive for patient safety. The Chief Medical Officer's report quotes three specific incidents, namely those arising in Stoke (1982–1991), Leeds (2004) and Glasgow (2006), as examples of preventable errors. Although IVD may have helped to detect these incidents, it would not, and does not, constitute a unique solution to any of them, and the subsequent incident enquiries did not recommend widespread in vivo dosimetry. In fact, the quality and safety of radiotherapy delivery has improved considerably over the past decade, in response to the reports and recommendations arising from these incidents. A huge amount of work has led to the implementation of formal quality assurance procedures in all radiotherapy centres and the requirement for large-scale IVD may therefore be reduced. In particular, "unsafe transfer of data" is quoted as a reason why errors occur in radiotherapy. This might have been true in the past when manual transcribing between one stage and the next increased the chances of human error, but the improving data transfer compatibility between treatment planning systems and linear accelerators has vastly reduced the requirement for the manual input of data. The presence in many centres of a simple plan-checking system provides confidence about the accuracy of monitor unit settings calculated by treatment planning systems.
Contemporary developments in radiotherapy delivery also question the viability of IVD as a robust quality control technique for the future. In intensity modulated radiotherapy, dose gradients may be high, and therefore can lead to spatially dependent measurement uncertainties. In image-guided radiotherapy, the relationship between incident field position and anatomy may be varied on a fraction-to-fraction basis, making the correct positioning of dosemeters problematic. The "hidden danger" in each of these cases is that an accurate calculation may implicitly be replaced by a less accurate measurement.
Approximately 100 000 patients receive radiotherapy annually. Although 200 IRMER*-reportable incidents have occurred in UK radiotherapy centres over the past 5 years, it is not clear how many of these incidents resulted in harm to the patient or how many would have been prevented by IVD. We hope that the suggestion of "hidden dangers" will not persuade patients to refuse radiotherapy and thus compromise their overall treatment.
In conclusion, IVD has a role to play in modern radiotherapy, but its applications may be limited and they should be chosen judiciously. More widespread implementation should be subject to a thorough analysis not only of the potential benefits but also of the possible detriments. We hope a multidisciplinary group drawn from all of the professions involved will collaborate in producing such guidance, so that patients will benefit from a coherent and effective framework for the assurance of their safety.
Footnotes
*Ionising Radiation (Medical Exposure) Regulations 2000 
Received for publication August 23, 2007. Accepted for publication August 23, 2007.
References
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A J Munro Hidden danger, obvious opportunity: error and risk in the management of cancer Br. J. Radiol., December 1, 2007; 80(960): 955 - 966. [Full Text] [PDF]
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