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Adding to this subject, Scanff et al [2] reported on population exposure to ionising radiation from medical examinations in France, and showed that CT accounted for 8% of procedures but 39% of the collective dose. Conventional radiography accounted for 90% of the total number of procedures but only 37% of the effective dose, whereas nuclear medicine and interventional radiology (IR) each accounted for 2% of procedures, but 7% and 17% of the collective dose, respectively. The per caput effective dose was between 0.66 mSv and 0.83 mSv.
The impact of CT risks was discussed further by Lautin et al [3] who advocated the need for radiologists to restrict CT scans to regions of interest, a view which was endorsed in an editorial that also drew attention to the earlier awareness of these risks among paediatric radiologists [4].
One of the recent causes of the growth in CT is the replacement of ventilation–perfusion (V/Q) lung scanning for the detection of pulmonary emboli with CT pulmonary angiography (CTPA). CTPA is becoming the standard method for demonstrating pulmonary embolism in the general population but there is limited guidance for pregnant patients. Doshi et al [5] estimated that the fetal dose from CTPA in late pregnancy was in the range of 60–230 µGy, which is similar to that produced by V/Q scans. Three strategies for dose reduction were investigated: (i) mA modulation, (ii) shielding with a lead coat and (iii) a 5 cm shorter scan length. These reduced the fetal dose by 10%, 35% and 56%, respectively, showing a dramatic reduction with shielding and a reduction in scan length without significantly affecting the rate of diagnosis. A modelling study by Iball et al [6] demonstrated that lead remained the shielding material of choice.
Staff doses from cardiac IR are linked to the corresponding patient dose because they arise mainly from radiation scattered from the patient. Morrish and Goldstone [7] found that exposure from scatter was about 16 times greater for digital acquisition than for fluoroscopy, and was greater for oblique angled imaging because of the increase in the related exposure factors. Their comprehensive evaluation of scattered radiation distributions in the angiography room should provide valuable material for the training of staff in the use of angiographic equipment and will aid occupational dose reduction strategies.
There is growing concern about deterministic effects to the skin resulting from IR procedures; Kawabe et al [8] showed that the simple and inexpensive measure of using an expanded polystyrene board to introduce an air gap between the couch and the patient resulted in skin dose savings of 
9% for an under-couch tube system.
Cardiac IR examinations have increased dramatically in recent years, and the population dose in 29 European countries from coronary angiograms, pacemaker insertions, percutaneous transluminal coronary angioplasties and stent procedures was estimated to be 27000 man.Sv [9].
Bedetti et al [10] conducted a study into the cumulative effective dose in patients in a cardiology ward. Three types of procedures were responsible for approximately 86% of the total collective effective dose: (i) arteriography and interventional procedures (12% of examinations and 48% of the average dose per patient); (ii) nuclear medicine (5% of examinations and 21% of the average dose); and (iii) CT (4% of examinations and 17% of the average dose). They highlighted that the median estimated extra risk of cancer induction (fatal plus non-fatal) was approximately 1 in 200 and emphasised the need to log cumulative dose for each patient. Justification and optimization were emphasised.
The referring doctor's knowledge of the radiation dose arising from CT examinations, and for that matter any radiological procedure, is one of the keys to managing radiation risk. A survey to assess awareness of radiation dose amongst 300 consultants and 200 junior doctors in Northern Ireland was carried out by Soye and Paterson [11]. Respondents were asked about the radiation dose from a chest radiograph and the annual dose from background radiation, and to estimate the radiation dose and cancer risk from several common radiological procedures. 153 questionnaires were returned. The mean score achieved was 39%. Only 26% of doctors achieved a score of 50% or more. Those who had received formal training about ionising radiation scored more highly than those who had not. The authors concluded that clinician awareness of radiation doses and the consequent risk to patients is poor, and that there is a corresponding need to educate clinicians.
There is an increasing number of examples in which IR is replacing conventional treatment. Takao et al [12] studied the outcomes of neurosurgical and endovascular treatment of ruptured intracranial aneurysms. In terms of life expectancy and subarachnoid haemorrhage-related mortality and disability rates, endovascular treatment was more effective than neurosurgery and was also more effective than neurosurgery over a lifetime.
Colorectal cancer is also topical, and this year four papers were published on various aspects of this subject. Taylor et al [13] reported that 1 day of focused training increases observer polyp sensitivity by 18% overall when using computer-assisted detection software. However, this was at the expense of increased reporting time (a median of 17.1 min compared with 9.3 min pre-training). In addition, specificity was reduced from a median of 2.5 false positives per 20 datasets pre-training to a median of 5.5 false positives per 20 datasets after training.
Burton et al [14] reported that CT has the potential to become the imaging modality of choice in the pre-operative prediction of poor prognostic features in colonic cancers. They developed criteria for predicting the T and N stage, involvement of the retroperitoneal surgical margin and the presence of extramural vascular invasion, and compared the high-resolution CT findings with histopathological results in 33 patients. They found that prognosis was correctly predicted by CT in 82–85% of cases.
With regard to MRI, Koh et al [15] reported that pelvic phased array MRI is useful in the local staging of anal carcinoma and for assessing tumour response. After treatment, a decrease in tumour size accompanied by reduction and stability of the MR T2 signal characteristics at 1 year after chemoradiation was associated with a favourable outcome.
A note of caution was sounded by Messiou et al [16], however, in their paper on pre-operative MR assessment in cases of recurrent rectal cancer. Differentiation of recurrent cancer from post-surgical or post-radiotherapy changes remains difficult when assessing the pelvic sidewalls, and the limitations of MR assessment in this situation need to be recognised.
Blamire [17], in his Hounsfield Review, anticipated future developments in MRI technology over the next 10 years and speculated that further improvements in technology, ultra-short echo time imaging and combined modality imaging would almost certainly develop more widely. The use of MRI as a functional tool was emphasised by Abou El-Ghar et al [18] who used MRI in chronic obstructive uropathy and compromised renal function. This provided the sole method for morphological and functional assessment, although the possible risk of nephrogenic systemic fibrosis in patients with impaired renal function indicates the need to minimise gadolinium dosage.
Disease classifications which were developed before advanced imaging was available are often in need of modification. Taylor et al [19] demonstrated that such a situation had developed with optic pathway gliomas and showed that a modified classification was a more appropriate tool in clinical trials of new treatments for this condition.
A salutary lesson was issued by Bermejo-Perez et al [20] in their review article on cancer surveillance based on imaging techniques in carriers of BRCA1/2 gene mutations. This systematic review points out that, of 749 articles retrieved, only 13 were appropriate for analysis and no definitive conclusion could be drawn on the performance of ovarian cancer surveillance in women carrying these mutations. Further work in this area is obviously essential.
Tissue characterisation is frequently regarded as the holy grail of imaging. In many studies, tissue characterisation has not been feasible but the paper by Moore et al [21] demonstrated distinct lymph node characteristics on ultrasound for breast cancer in patients at high risk for axillary metastases. They suggest that a combination of ultrasound and aspiration cytology could modify the surgical approach to the axilla. Likewise, the paper by Van As et al [22] on diffusion-weighted MRI in radical prostatectomy specimens shows quite convincingly that there is a difference in the apparent diffusion coefficient between benign tissue and cancer.
The majority of publications of relevance to oncology dealt with the technology of delivering radiotherapy. Intensity-modulated radiotherapy (IMRT) is moving steadily into clinical practice. We now have evidence, albeit small-scale, that the technology can deliver its promise of reducing the long-term toxicity of radiotherapy [23, 24]. It will be interesting, with a longer follow-up, to see whether what is being seen here is a true decrease in incidence or simply a prolongation of the latent interval between treatment and its adverse effects. Plowman et al [25–27] have published several papers in the BJR this year in which they have explored the dosimetric, and implied clinical, advantages of tomotherapy. This technique, primarily because it requires specialised equipment (as opposed to being capable of implementation on a modern linear accelerator), is not widely available. We are reaching a point at which we need to have well-conducted analyses of the cost-effectiveness of the various competing approaches if we are to plan logically for the technological future of radiation treatment delivery. We need to know how much we will actually achieve, in terms of improvements in local control, survival and morbidity, from the wider implementation of these technologies. The costs are important — not just the money, but also the time, training and opportunity costs of introducing techniques that can tie up several hours of a radiation oncologist's time simply to enter target volumes and the volumes of organs at risk. Images are needed in order to define a target volume and ensure that it is being treated adequately. Kim et al [28] carried out a national audit to assess the extent to which the Royal College of Radiologists' guidelines on the use of intravenous contrast during radiotherapy planning procedures were being followed. Their results were disappointing in two respects: (i) only 35 out of 50 managers responsible for radiotherapy departments were aware of the guidelines and (ii) no centre was able to provide a level of service that fully adhered to the guidelines. So it would seem that we may be able to irradiate targets with a high degree of accuracy, but we may be using suboptimal methods to define the targets in the first place. (Of course, we could just rely on the radiologists' reports on the diagnostic images but these may have errors, particularly if voice recognition software is being asked to deal with Aberdonian speech [29].) The paper by Harrison [30] reminds us that as we improve the quality of our work we may, paradoxically, be undermining it. Repeated imaging, for localisation and verification, will contribute significantly to the amount of low-dose radiation we deliver to potentially vulnerable tissues. The biological consequences of this are unpredictable and, particularly for adjuvant therapy, highly relevant in terms of an overall cost–benefit ratio.
There is, of course, a future for radiation oncology that is not directly dependent on technology. Combining drugs and radiotherapy has always been a tempting approach — one that, in an ideal world, offers synergistic benefit and sub-additive toxicity. The BJR Special Issue on "New Agents in Clinical Oncology", published in October 2008, drew clinicians' attention to several promising molecules. The challenge for the future will be to carry out the clinical studies that are required to define the role and utility of such agents in everyday practice.
HON. EDITORS and DEPUTY EDITORS
References
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