Does Overall Radiologic Exposure in the Post-COVID-19 Era Matter?

The recent coronavirus (COVID-19) outbreak negatively affected different aspects of human life in recent years. While the disease has had considerable direct burden in almost every country, there are many indirect impacts of the outbreak that may affect human life during the post-COVID-19 era. We believe there were excessive imaging studies during the early stages of the pandemic, especially in countries where the molecular diagnostic tests were unavailable. Therefore, using lower radiation doses for diagnostic techniques or considering other diagnostic modalities for diagnostic or follow-up purposes should be employed.

The recent COVID-19 pandemic is still a big concern for almost every society, and despite the recent advances in vaccination, many countries faced multiple waves of the disease. COVID-19 was first introduced in Wuhan city (China) and has been considered a pandemic since mid-March 2020 (Cucinotta and Vanelli 2020). Every symptomatic individual or those who had suspicious contact with infected individuals were candidates for molecular testing of COVID-19 or a lung computed tomography (CT) scan if respiratory symptoms were present. Lung CT scan is considered a reliable diagnostic modality for COVID-19 disease and is frequently used in many clinical settings, including in countries dealing with a low vaccination rate and a considerable number of new cases each day (Rassouli et al. 2020).

Although a single CT scan may not be a considerable lifetime cancer risk for adults, the scan could be more harmful to younger patients with longer life expectancy. Moreover, repeated scans even in adults increase the risk of cancer in the future (Cristofaro et al. 2021). The first population-based longitudinal study based on the health insurance data of 3,387,703 individuals from Taiwan revealed that exposure to medical CT scan radiation is associated with leukemia and thyroid cancer in adults (Shao et al. 2020). However, the most recent systematic, methodologic review, not including the latter article, demonstrated that 21 out of 25 high-quality studies included in their analysis did not support cancer development following low-dose radiation exposure (Schultz et al. 2020). The authors stated that exposure to multiple CT scans with a cumulative dose of up to 100 mSv (equal to 10 CT scans) will not increase the cancer risk (Schultz et al. 2020). The result of this study increased the previously reported threshold for cancer development as some guidelines considered the annual radiation limit as 20 mSv y⁻¹; performing at least three lung CT scans would pass this limit (Kellerer and Nekolla 1998). Although there are controversial results about the threshold for the development of cancer following CT scans, there is no doubt that excessive medical radiation exposure could have a harmful effect in the future, and we think that the recent pandemic may negatively affect the incidence of future cancer from radiation exposure.

Although COVID-19 could be diagnosed with a single lung CT scan, during the COVID-19 pandemic, some people underwent multiple CT scans varying from three to even eight times, and some may have been reinfected and then underwent numerous imaging studies again (Cristofaro et al. 2021). A recent interview with the head of the Radiological Society of Khorasan on the social media of “Islamic Republic of Iran News Agency” on 17 August 2021, revealed that there were 3,000 CT scans performed daily in Mashhad city (the second most populous city in Iran) because of possible COVID-19 (new COVID-19 cases on 17 August 2021 totaled 50,228 in Iran) (“2021 Mashhad up to 3,000 cases",). Alongside such a considerable number of daily CT scans of suspected COVID-19 patients, those undergoing chest CT scans received significantly more overall mean radiation doses than patients infected with other infectious diseases undergoing CT scan during a similar period before the pandemic (Cristofaro et al. 2021). Despite the lack of assessment of risk and benefit of follow-up CT scans (Bazdyrev et al. 2021), some patients may need to repeat their CT scan, such as those with worsening symptoms with negative RT-PCR and may receive considerably higher radiation (Mahdavi et al. 2020).

Unfortunately, scan protocols are widely varied across different radiology facilities worldwide, and many facilities may not use the low dose protocol for imaging COVID-19 patients. The risk of increased overall radiologic exposure becomes evident considering the follow-up CT scan in the recovered patients who develop pulmonary diseases. At the same time, it has been demonstrated that a considerable number of recovered patients will have respiratory symptoms, including dyspnea. Emerging new clinical insights regarding the pulmonary complications following COVID-19 infection, including persistent post-COVID-19 interstitial lung disease, warrants lung CT scan follow-ups in at least 10% of hospitalized patients developing lung fibrosis (Bazdyrev et al. 2021). The last concern regarding the growing number of CT scans would be because of the overlap of COVID-19 disease with other pulmonary diseases. Even despite the ongoing COVID-19 vaccination in Iran and regarding the decreasing number of COVID-19 cases around the globe, during the influenza seasons, we may face performing even more CT scans compared to the similar months before the pandemic because of overlapping of COVID-19 symptoms with influenza infection (Radmard et al. 2020).

In such a complicated situation, with an unclear future of the disease regarding the possible emergence of novel variants (Reardon 2021), we believe that radiologic societies, especially in underdeveloped and developing countries, should reduce the possibly harmless effects of unnecessary CT scans. According to the US Food and Drug Administration (2017), by considering the average effective dose of 10 mSv (ranging from 1 to 18 mSv; Mettler et al. 2008) for a chest CT scan, the risk of developing fatal cancer will be approximately 1 chance in 2,000. Regarding the natural chance of fatal cancer as 400 in 2,000, the total risk may rise to 401 in 2000, which seems to be a slight increase at first look. However, such a small risk may become a public concern when many individuals undergo CT scans. Therefore, clinicians should limit lung CT scans and consider molecular detection techniques as the first diagnostic approach in symptomatic patients.