To the best of our knowledge, there is nowadays no dedicated longitudinal observational study on quantification and justification of radiation doses in patients with ILDs. Our study demonstrated that patient did not experience a harmful over-irradiation over the time. Nevertheless, we noticed that overall justification of the chest CT-scans was weak, out of those dedicated for acute clinical deterioration, which are in line with guidelines recommendations in the event of an ILD exacerbation ().
Our population is like what is generally seen in chronic ILD populations, with an increase prevalence of CTD-PF due to the bias induced by the recruitment in our hospital, as a tertiary center. The demographic characteristics are in line with those classically seen in patients suffering from ILD (,).
In our study, clinicians performed an average of 1.7 scans / year / patient. We therefore observed a concordance between the a priori indication and the a posteriori validity of the scanners. The approach showed us that, overall, 56.9% of scanners were justified a priori, whereas 60.15% of them were justified a posteriori. We therefore defined the unjustified CT-scanner as a CT-scanner performed systematically without clear clinical indication or expected result inducing no specific clinical or therapeutic response. In our study, we therefore identified that 40% of the performed CT-scans were not justified.
As indicated by the ERS guidelines, which define an ILD exacerbation based on a drop in FVC or DLCO or the need for oxygen support, PFT is seen as a useful parameter (). Therefore, PFTs and their degradation over time, such as a drop of 10% or more in FEV1 or FVC, represent an interesting monitoring tool which allows us to study the evolution of ILDs, and could possibly lead to a therapeutic implication in our patients. Based on the ERS recommendations defining significant deterioration in DLCO and FVC, we tried to correlate the number of CT-scans performed with the drop in FVC and DLCO experienced by some patients over the time. Interestingly, we didn’t identify any specific correlation between those parameters, neither for FVC or DLCO. The absence of correlation possibly due to the low number of acute exacerbation that will only slightly increase the number of CT scans (). The drop of DLCO is
Facing those observations, we raise the question of the cost-effectiveness of the routine CT-scans in patients suffering from chronic ILD. Indeed, it emerges that a significant number of CT-scans are prescribed without any diagnostic and therapeutic consequences, suggesting that clinicians are performing some of those explorations in a procedural way, regardless of the result of the PFTs modification over the time. The question of the occurrence of lung cancer in this specific populations has to be addressed in order to define the most relevant way to follow those patients.
Of interest, we’ve demonstrated that only a small proportion the CT scans were low dose CTs. While it seems obvious to explore lung parenchyma through high resolution CT-scans during the initial evaluation and diagnosis work-up, it is reasonable to assume that systematic imaging during follow-up low dose could be achieved with low-dose acquisition CTs specifically for lung cancer screening purpose (10). Considering low dose CT scans for basic monitoring could imply a reduction in the irradiation of our patients. Of note, only a minority of the images are contrast-enhanced CT scans.
In our study, it appears that few CT scan were performed in an emergency setting (8%), which is in keeping with the low prevalence of acute exacerbation of ILDs corroborated in literature 4–20% ().
This study is the opportunity to raise a specific concern focusing on the accurate evaluation of the benefit/risk balance of multiple CT scan evaluation in patients suffering from chronic fibrosing ILD. Indeed, it appears that PFTs and clinical evaluation can help to quantify sufficiently, in a routine-based follow-up, the evolution of the disease. Therefore, global irradiation could possibly be reduced by individuating the imaging acquisition modalities to each patient and situation. Of interest, we’ve noticed that the majority of not-routinely-based CT-scans (ie. Emergency CTs or CTs consecutive to clinical or functional deterioration) are justified on a clinical basis, highlighting the absolute usefulness of chest CTs in this precise context. Moreover, the concept of accurate follow-up through CT imaging must be put into perspective with lung cancer screening. Indeed, systematic lung cancer screening is not specifically recommended in ILD patients and is committed to personalized and individualized work-up. More specifically, ILD patients exhibit an increased risk of developing lung cancer (smoking history, scaring process, use of immunosuppressive agents,). Therefore, clinicians have to be cautious to reduce global cumulated irradiation over the time due to their ILD follow-up. Implementing a public health perspective, the overall increase in health care costs implies a rationalization of the use of complementary examinations in chronic diseases.
Out of economic considerations, it is important to note that the average irradiation level was 34.9 mGy and 1095 mGy * cm per year and per patient (18.6 mSv), which remains high enough to induce stochastic effects after a few years. The incidence of lung cancer in the general population is 100/100000 inhabitants (i.e., 1% / year) (). In smokers, the risk of having lung cancer is 10 to 30 times higher than in a non-smoker population (). In a review of the literature, the percentage of lung cancer with patients suffering from ILD is 9.8–20% depending of the time of follow-up, the risk globally increasing over the time (). In our study, the global level of lung cancer is similar to what is seen in literature (7%), with a median follow up of 3.7 years (). In the literature, to the best of our knowledge, there are nowadays no long-term studies reporting the effects of radiation on the lung or breast. Such a study would be welcomed but would require a larger population associated to a longer follow-up.