Interventional radiology at the meetings of the German Radiological Society from 1998 to 2008: evaluation of structural changes and radiation issues

IR has proven to be a stable and appreciated topic at the DRK—the largest congress of radiology in German-speaking countries and the third largest congress in Europe. With a proportion of IR abstracts between 15 and 20% of all contributions, IR rose significantly in absolute numbers to a peak of 200 abstracts in 2005. This was primarily based upon structural changes of the DRK in the latter years clearly emphasising educational activities for radiologists and technicians and eliciting a substantial and significant growth of educational IR contributions. Given the increasing overall demand for educated staff in radiology, this is an impressive answer to persisting voices arguing for high-level education to ensure the availability of properly trained radiologists [12–15]. In combination with the static time frame of the DRK, scientific IR contributions therefore declined only non-significantly. With 9–13% being prospective contributions, IR kept within an equal share of prospective scientific abstracts compared with general radiology [10]. The triplication of relative numbers for prospective contributions may be a calculation effect based on declining numbers of all scientific contributions and increasing numbers of prospective abstracts. Furthermore, absolute numbers of prospective contributions remained—under postulation of evidence-based medicine as the goal—quite small. This correlates to the warning comments of several authors about the amount and quality of IR literature and, moreover, demonstrates that despite requests for more research activities in IR [13, 16–18], only moderate increases of high-ranking studies have been reached in absolute numbers. Nevertheless, even when based on small absolute numbers, significantly more prospective research in IR has been presented at the DRK. The conflicting demands of raising absolute numbers of high-ranking prospective studies, managing increasing clinical workloads and—on the other hand—maintain the intensified educational activities, evidently advocate against further cutbacks in the equipment, manpower and funding of IR.

Image-guidance is without question an essential prerequisite of modern IR procedures. Given the clear advantages of CT imaging mentioned above, the rising demand of CT examinations in total and for CT-guided IR procedures is not surprising. Mettler et al. [19] reported in 2009 a tenfold increase in the number of all radiological procedures from 1950 to 2006 in the United States with a rise in the annual per-capita effective dose of 600%. Citing a report of the National Council on Radiation Protection and Measurements, they presented an estimated number of 67 million CT examinations and 17 million interventional procedures in 2006 in the United States. With respect to IR, 72.2% of all interventional or catheterisation procedures in 2006 in the United States were non-cardiac diagnostic or therapeutic procedures applying 46.9% of the total collective dose with vascular, urinary and myelographic procedures being the most common areas of IR. Our results clearly show the significantly increasing use of CT with declining or stable proportions of MRI and other imaging modalities. The presented data indicate a shift of IR activities at the DRK from angiography-based vessel interventions to CT-guided procedures of the trunk: The traditional IR field of vessel interventions showed a drop in relative proportions with the main increment of IR being revealed within the regions of chest, abdomen, and the musculoskeletal system. These body regions mainly represent areas with the most-radiation-sensitive organs. In addition, the resulting effective doses of imaging procedures of the trunk—regardless of the chosen ionising imaging modality—are highest compared with all other body regions [20].

Based on the linear no-threshold model, low-dose diagnostic radiation exposure (<100 mSv) accounts for a low but tangible risk of carcinogenesis [21–23]. Recent studies even report evidence for an increased risk for solid tumour development with exposures at a magnitude of 10–50 mSv [24–27]. Effective doses of fluoroscopic or angiographic IR procedures—especially when concerning the trunk as in embolisations or transjugular portosystemic shunt implantations—can be associated with a substantially increased likelihood of clinically significant patient doses [28]. As presented by Tsalafoutas et al. [29], median effective doses for CT-guided biopsies were about 23 mSv, for radiofrequency ablations 35 mSv, for abscess drainages 16 mSv and for nephrostomies 11 mSv. The maximum effective dose of these procedures reached 57 mSv and the unavoidable diagnostic part of the CT-guided intervention produced the lion’s share of radiation exposure. Although even these values of higher expositions are considered as “low” (i.e. one per 1,000 individuals) according to the proposed adequate risk terms of the UK Department of Health [30] compared with the general lifetime risk of cancer development, they are definitely above the effective doses accompanying most diagnostic procedures. Moreover, the increasing demand and sometimes repeated use of IR procedures make radiation protection an important issue. Studies revealed sobering results of the awareness and knowledge of non-radiologist healthcare professionals concerning the magnitude of radiation exposure combined with different radiological examinations, leaving a potential question mark on their ability to balance the risk-benefit ratio for a given patient [31–36]. Thus, interventional radiologists are by all means the primary correspondents of dose issues accompanying IR procedures. Despite small absolute numbers through the years for all dose categories, the presented results of our study demonstrate an increase in the awareness and occupation with radiation exposure measured in percentages of abstracts dealing with this topic at the DRK during the study period—concomitant with the above mentioned increase of IR abstracts in general. The significant increase of contributions in IR relating to dose reduction is especially encouraging. Obviously, the growing use of IR and ionising imaging modalities does not remain unanswered by interventionally acting radiologists with respect to radiation protection efforts. Nevertheless, compared with an analysis of general radiology and paediatric radiology in this 11-year period of the DRK presented elsewhere [9, 10], percentages of dose relevant contributions were lower in IR—especially for contributions with relation to CT. Furthermore, even when considering multiple naming for these dose categories, 94% of all IR abstracts at the DRK did not mention radiation exposure at all—despite the above-mentioned increasing trend towards CT as the guiding instrument. Finally, looking at the absolute numbers of all IR contributions, of IR contributions pertaining to ionising procedures and for dose-related IR contributions (Table 2), the last category—even if growing—is clearly outnumbered.

Moreover, many abstracts did not report the target variable of radiation exposure—i.e. effective dose—for the mentioned procedures (neither expressed as typical doses for a given procedure nor based on their own calculated radiation data). This could have been for several reasons. First, effective dose as a calculated but not measurable variable represents in itself a concept that is combined with a relative uncertainty of up to 40% [30]. Some factors may influence the calculation of effective dose, especially factors as tissue weighting, scanning devices, region-based or organ-based calculation method and, finally, the patient’s habitus compared with the proposed body model. Additionally, for some body regions tissue weighting factors are not disposable. Hence, some authors may have chosen to avoid the calculation of effective doses in favour of reporting measurable variables as the dose-length product orCT dose index. Moreover, the majority of evaluated abstracts concerned retrospective studies. It may have been impossible or to difficult to collect these data retrospectively—especially if radiation exposure was not in the focus of interest. Nevertheless, the seldom reporting of effective doses contradicts the intended use of this variable as a dose quantity that is easy to compare and—with respect to all its uncertainties—links the measured radiation dose to the risk of health detriment. Hence, it may be technically more precise to report the dose-length product or CT dose index, but the associated risk with a given procedure or for a given reference patient is not displayed. The contrast between this situation and the role of interventional radiologists as experts in radiation protection is potentially problematic. Moreover, it may be difficult to communicate to an incrementally attentive public, as issues dealt with at the DRK are frequently presented and discussed by the lay press. Given the interdisciplinary character of IR and the known turf battles around interventional medicine [1, 37, 38], deficiencies in the key qualification of radiation protection may ultimately heat discussions, which is why radiologists should be the primary experts and correspondents of IR. If radiologists want to maintain primacy in IR, further development of radiation protection knowledge based on intensified their own high-ranking research could be a cornerstone and unique selling proposition to succeed.

There are several limitations of this study, most important being the above-mentioned assumptions, upon which the evaluations were based. The first hypothesis, that the published abstracts contain all pertinent findings, does not exclude radiation exposure as a topic to be touched upon in the contribution but is not expressively mentioned in the abstract. Nevertheless, an author considering radiation exposure important enough to be discussed at the oral presentation, but not as eminent to be mentioned in the abstract, reflects an attitude towards the subject that is in itself problematic. Secondly, the DRK may not accurately reflect the current state of all scientific proceedings in Germany or other German-speaking countries. Moreover, as the number of accepted abstracts will have been different from the number of submitted abstracts to a given subject, there may have been several factors influencing the decision process of accepting contributions for the annual meetings of the DRK, including structural changes as mentioned above or the wish to even out contributions over different topics. But again, as the largest congress in the above-mentioned countries, there will be no better platform for such an analysis concerning the handling of ionising imaging modalities and dose in IR. Furthermore, the categorisation of the abstracts was intrinsically not immune to subjectivity, but over 11 years of annual meetings this would result in a systematic error probably factoring itself out. Moreover, because of the chosen study design, other indirect forms of radiation exposure reduction could have been missed. If, for instance, a study with comparison of an ionising and non-ionising imaging method in IR results in non-inferiority of the non-ionising imaging method, then this would also be a contribution to dose reduction, but would not have been included in our analysis. Finally, the question for the appropriate proportion of abstracts in a congress programme dealing with radiation exposure and dose reduction remains open.

In conclusion, IR emerged as a substantially growing specialty of radiology at the DRK from 1998 to 2008, with significant increments of educational activities and prospective research contributions. Despite a significant trend towards CT as an IR imaging modality, radiation exposure of IR was rarely in the focus of interest. Nevertheless, contributions relating to dose reduction demonstrated an encouraging and significant growth during the study period.