Towards Safer Radiotherapy

discussion with physics should occur. Changes should be documented and the entire
prescription verified in accordance with written procedures to ensure accuracy of the data.
Recommendation
Checks and verification should be performed independently by entitled operators working to
clear protocols, which make explicit the individual’s responsibilities and accountability.
5.11 On-treatment imaging
All the check and verification procedures in radiotherapy leading up to treatment are checks of the
individual steps of the process. Only two types of checks currently available monitor the outcome of
the overall process for individual patients; these are:
i. Portal imaging which can detect geometric errors
ii.
In vivo dosimetry which may detect dose errors.
Geometric verification is critically important in the delivery of radiotherapy but is not dealt with in
detail here as guidance is provided in Geometric uncertainties in radiotherapy: defining the target
volume 80 and one forthcoming publication. 77 Portal imaging used at the start of a treatment course
provides an opportunity to ensure that there is not a gross set-up error.
45
Recommendation
All radiotherapy centres should have protocols for on-treatment verification imaging. This should
be used as a minimum at the start of a course of radiotherapy to ensure there is no gross
positional error. If there is no electronic portal imaging available then film verification should be
used if technically possible.
5.12 In vivo dosimetry
5.12.1 In vivo dosimetry not only has the potential to detect dosimetric errors but also, if carried out
at an early stage in the course of treatment, may allow corrective action to be taken. It is,
therefore, an effective method of reducing potential harm to patients and has been
recommended by the International Commission on Radiological Protection (IRCP). 81
The uptake of routine in vivo dosimetry for all patients has been patchy in the UK and only
30 to 40% of centres currently practise routine in vivo dosimetry at the beginning of
treatment either for all patients or for subsets of patients. 82 Cost and practicality have been
cited as reasons for not implementing in vivo dosimetry widely. These issues have been
summarised elsewhere. 83 It is accepted that the setting of priorities has to balance the costs
and benefits. However, the potential benefits to patients are reinforced by the imperative to
maintain public confidence in radiotherapy as a safe form of treatment. In vivo dosimetry has
now been recommended as a routine procedure by the Chief Medical Officer for England. 84
It is already a legal requirement in Denmark and Sweden and will shortly be so in France. 85
It is unusual to detect an error using this method, 83 but major overdoses do, on rare
occasions, occur and should be detectable using this system. 5–7
Towards Safer Radiotherapy