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Randomized Controlled Trials for Diagnostic Imaging: Conceptual and Pratical Problems

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Abstract

We raise a problem of applicability of RCTs to validate nuclear diagnostic imaging tests. In spite of the wide application of PET and other similar techniques that use radiopharmaceuticals for diagnostic purposes, RCT-based evidence on their validity is sparse. We claim that this is due to a general conceptual problem that we call Prevalence of Treatment, which arises in connection with designing RCTs for testing any diagnostic procedure in the present context of medical research, and is particularly apparent in this case. We also identify three practical reasons why RCTs do not qualify as the best option for PET validation, which have to do with specific characteristics of nuclear diagnostic imaging, and of radiopharmaceuticals. The paper is meant to contribute both to the philosophical discussion on the EBM hierarchy of evidence, and on the specific debate on radiopharmaceuticals in nuclear medicine.

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Notes

  1. There are many accuracy studies in the literature, that compare FDG PET-CT with standard diagnostic tests in specific areas (See e.g. Czernin et al. 2013 for a review).

  2. Other factors, alternative to treatment, that may intervene in the causal chain from test to clinical benefit are change in time-frame of management (i.e. speeding up decisions), and alterations of patients’ and clinicians’ perception of the situation. Such factors are even more difficult to measure with an RCT than test-plus-intervention clinical benefit (Di Ruffano and Deeks 2016).

  3. Arguably, there are cases in which PET can have a direct clinical benefit, namely when it replaces an invasive procedure like surgical staging. Is it possible to design a RCT to assess the direct clinical benefits of nuclear medicine imaging techniques, in such cases? Yes, but it would not be necessary, and therefore not appropriate, as the positive clinical (avoidance of the invasive procedure) is immediate, and there is no need to monitor the two groups of patients (invasive versus non-invasive procedure) over time. Here, the characteristics of RCTs methodology make them not recommendable (Vach et al. 2011).

  4. We are not claiming that the Predominance of treatment problem is generalizable a priori to all diagnostic tests. That there is a Predominance of treatment problem, derives from the requirement that medical diagnostic tests are evaluated at least partially in terms of their clinical benefit, which is a contingent feature of current healthcare and scientific regulative practices Therefore, it is surely possible that no such problem (mutatis mutandis) arises with other diagnostic tests, e.g. in engineering or robotics. We thank an anonymous reviewer for this point.

  5. As suggested by a reviewer of this Journal, a possible direction of inquiry could be on the possibility of qualifying or partially suspending the Principle of Equipoise, either when applied to tests on diagnostic procedures, and not on treatments, or when research is conducted with the declared aim of providing treatment. This suggestion deserves to be discussed on a separate paper.

  6. For a philosophical discussion of consensus conferences, see Solomon (2007).

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Authors and Affiliations

  1. Department of Psychology, Milano-Bicocca University, Milano, Italy

    Elisabetta Lalumera

  2. Department of Nuclear Medicine, S.Orsola University Hospital, Bologna, Italy

    Stefano Fanti

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  1. Elisabetta Lalumera
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  2. Stefano Fanti
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Correspondence to Elisabetta Lalumera.

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Lalumera, E., Fanti, S. Randomized Controlled Trials for Diagnostic Imaging: Conceptual and Pratical Problems. Topoi 38, 395–400 (2019). https://doi.org/10.1007/s11245-017-9535-z

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