The debate over performing a CT scan for COVID-19 testing has been on for quite some time now. Whether a CT scan can be a first-line test to diagnose the disease or is it just an expensive formality, has been a common question in the medical world too. In this article, we present clarity over these issues.

For our comprehensive coverage and latest updates on COVID-19 click here.

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Introduction

The World Health Organisation declared the outbreak of COVID-19 as a pandemic on 11 March 2020. As of July 15, 2021, Worldometer recorded over 189.3 million cases of COVID-19 globally. Over 4.07 million people died. Scientists developed many effective vaccines. Many countries vaccinated notable fractions of their populations. Others are still catching up. Concerns about the new variants persist. The medical community worldwide is at the forefront to diagnose the disease, offer valuable medical care based on their observations even when hundreds of patients overwhelm them and more importantly to isolate the patients to prevent further spread of the disease.

According to physicians managing the disease, CT scan has no role as a first-line test to diagnose the disease, though some radiologists wonder whether non‐utilisation of computed tomography as a public health tool is a costly lapse in closing the pandemic.

This conflict among physicians needs early resolution. Guideline-writing professionals seldom lower the bar. They vigilantly prescribe science-based, robust guidelines.

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Overuse of CT scan units

A White paper from the Society of Chest Imaging and Interventions (SCII) has described the conditions in India thus:

“India, in April 2021, is in the throes of a second pandemic that is proving to be worse than the first one last year. Compared to most Western countries, CT scan has become a de facto modality for patients with suspected or proven COVID-19. Most of these scans are not indicated and the irrational use of the CT scans is placing an economic, logistical and eventually an overall increased radiation burden on society. This can also have an adverse psychological effect when coupled with the use of other unnecessary tests.”

The Society with members who have a combined experience of more than 200 years practising thoracic radiology urged that CT scan units must not be used for routine screening.

Dr Mandeep Garg, Professor of Radiology, PGIMER, Chandigarh, the lead author of a paper aptly titled 'Computed tomography chest in COVID-19: When & why?' (Indian Journal of Medical Research, 26 March 2021) disclosed that he gets several CT scans for review every day, most of which, the patients may not need in the very first place. (The Tribune, 5 January 2021).

A Google search may reveal how this uniquely useful diagnostic tool is marketed thoughtlessly in this pandemic era. CT scan use continues nationwide, reportedly in many cases even without any reference from physicians. That is why the Central government issued an advisory on the topic on 7 June 2021.

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Advisory on Rational Use of High-Resolution CT (HRCT) imaging in Patients with COVID-19 (Issued on: 7th June 2021)

The preamble of the new Advisory (7 June 2021) said.

“The Ministry of Health and Family Welfare (MOHFW), All India Institute of Medical Sciences ( AIIMS) and the Indian Council of Medical Research (ICMR) have jointly issued treatment guidelines for COVID-19 patients in the form of a guidance/ algorithm on 23rd April 2021 This guidance/ algorithm is easy to understand, practice and is widely followed. But this guidance/ algorithm does not prevent misuse/ overuse of HRCT Scan as an investigation tool in COVID-19 patients.”

The Joint Monitoring Group under the Chairmanship of the Director-General of Health Services (DGHS) realised the need to stop the irrational use/overuse of High-Resolution CT (HRCT) Scan as an investigation tool on COVID–19 patients.

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Situations when HRCT imaging of chest should not be done

HRCT scan chest should not be done for the purpose of diagnosing/screening COVID-19 infection. Diagnosis of COVID-19 should be done only by using approved laboratory tests (RT-PCR Test) as recommended by the ICMR.

1. It is not indicated in people with asymptomatic COVID-19.
2. It is not required to initiate treatment in COVID-19 patients with hypoxia and an abnormal chest radiograph.
3. It is not required to assess response to treatment. More often, the lung lesions show radiological progression despite clinical improvement.

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Appropriate indications for HRCT imaging of the chest in COVID-19 patients

• Suspect/confirmed case of moderate COVID-19 who continue to deteriorate clinically even after initiation of appropriate therapy
• Treating physician/intensivist may consider HRCT chest depending on clinical assessment of the patient

In view of the above, treating physicians should exercise caution while advising HRCT imaging of the chest.

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The Advisory concludes

The White Paper from the Society of Chest Imaging and Intervention has stressed the importance of reducing:

“The rate of unnecessary CT scans done as a routine test in people, just because they are suspected to or have COVID-19, or just because patients demand that CT scans should be done because they have been led to believe via social media that the information from CT scans makes a difference.”

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The public spat between Dr. Guleria and IRIA

A public spat between the office-bearers of the Indian Radiological and Imaging Association (IRIA) and Dr Randeep Guleria, Director, All India Institute of Medical Sciences (AIIMS) inadvertently brought the conflict on some aspects of CT scan use among physicians into the public domain.

Dr Guleria MD (General Medicine) and DM (Pulmonary Medicine) is the Director of All India Institute of Medical Sciences, Delhi. He is the most authentic and trustworthy commentator on COVID-19, assuring millions of TV viewers and compatriots across the nation assuring them calmly with his erudite replies on the ever-changing moods of the pandemic. Anyone explaining the clinical aspects of COVID-19 to him is holding a candle to the sun.

“The IRIA is the largest radiology association of Indian radiologists in Asia with member strength of more than 18,000.” IRIA’s current President, Professor Amarnath Chelladurai, Professor and Head of Radio-diagnosis, Government Stanley Medical College, Chennai in just under 800 words lucidly explained some of the activities of IRIA in “Innovations in Imaging and Radiotherapy- A more connected world” a publication (June 9, 2021) of the British Institute of Radiology.

At a press conference in Delhi, Dr Guleria warned the community about the misuse of CT scans and biomarkers by patients having mild COVID-19 symptoms and said that the overuse of CT scans increases exposure to radiation that in turn escalates the risk of cancer (The Hindusthan Times, May 3, 2021).

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The news as published in The HT (verbatim)

Dr Guleria warned, "No point in conducting CT scans for mild cases; one may find patches in CT scan even if he/she is asymptomatic but may get cured easily. 1 CT scan = 300-400 Chest X-rays. With frequent CTs, risk of cancer in later life increases, for youngsters."

Dr Guleria addressed the misuse of diagnosis, which he said is not required in case of mild symptoms. "A lot of people are getting CT scans done and deem it important if their COVID tests turn out to be positive," he said. He cited a study that has shown patches in the CT scan of around 30-40 per cent of asymptomatic COVID-19 patients, which got cleared without any treatment. He used the study to make it clear that in case of mild infection, under home isolation with no problem or decline in saturation there is no use of a CT scan as some patches will appear.

Indian Radiological and Imaging Association (IRIA) issued a press statement on 5th May 2021 characterising some of Dr Guleria’s statements as “outdated", "unscientific", "irresponsible", "misleading" “alarming”, etc.

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IRIA press statement on 5th May 2021

Besides responding to Dr Guleria, the IRIA press release highlights issues such as the merits of CT scans over RT-PCR for diagnosing COVID-19 under certain conditions and other clinical matters. It revealed that for some reason several state governments have asked the radiology departments to notify patients with CORADS scores of 4 or 5. If IRIA is convinced about the rationale for such an action, they must expressly convey it to the central government which, after due consultation with specialists, may inform all other state governments for their benefit.

IRIA’s statement that one of the reasons for RT-PCR giving negative results is due to mutant variants is not correct. The Ministry of Health and Family Welfare clarified this issue thus on 16th April 2021 (verbatim): “The RT PCR tests being used in India do not miss these mutations as the RT-PCR tests being used in India target more than two genes. Sensitivity and specificity of the RT-PCR tests remain the same as earlier.”

Why IRIA publicly raised controversial issues such as RT-PCR vs CT scan to diagnose COVID-19 is not clear. What is the role, the IRIA expects the public to play in this matter? If IRIA has more appropriate guidelines on the use of CT scans during the pandemic they must convince the ICMR, Ministry of Health and Family Welfare, Institutions such as AIIMS, Postgraduate Institute of Medical Education and Research (PGIMER) etc and get them included in the official guidelines.

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CT scan units to diagnose COVID-19

The IRIA statement, read with the references gives the impression that in view of the pandemic some radiologists want to use CT scan units as a first-line test to diagnose COVID-19. Indeed an editorial titled “Was non‐utilisation of computed tomography as a public health tool a costly lapse in closing the pandemic” in the Indian Journal of Radiology and Imaging (IJRI, online on 23 January 2021) advocates CT use as a “public health tool”. This suggestion remains uncontested. Maybe, many members of IRIA endorse the suggestion.

Those who promote a pivotal role for CT scan units in diagnosing COVID-19 relying on earlier Chinese papers will think twice if they read the paper titled “Chest Computed Tomography for Detection of Coronavirus Disease 2019 (COVID-19): Don't Rush the Science”, Dr Michael Hope wrote in Annals of Internal Medicine (21st July 2020).

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Views of National and Regional agencies

Using CT scan for diagnosing COVID-19 is inconsistent with the guidelines of agencies such as the American College of Radiology (ACR), the European Society of Radiology (ESR), the European Society of Thoracic Imaging (ESTI), Canadian Society of Thoracic Radiology and the Canadian Association of Radiologists among others.

Initially, the National Health Commission of China included chest CT findings as evidence of a clinical diagnosis of COVID-19 for patients in Hubei province. However, the commission removed it from diagnostic criteria in the sixth version published on February 19, 2020. Presently, China wants the final diagnosis of COVID-19 should be confirmed by positive RT-PCR or gene sequencing.

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Expert statement

The main issues from Dr Guleria’s statement which IRIA opposed are:

1. Some of the limitations of CT scans, the dose used in chest screening compared to that from chest x-ray examination, and the cancer-inducing potential of low dose radiation.
2. Expressing dose from any diagnostic X-ray examination in terms of dose from chest x-ray tests, the most common examination which exposes the patient to low doses of X rays is a customary practice. Another method prevalent now is to express radiation dose in medical X-ray procedures in terms of the weeks or months or years of exposure to natural background radiation. Dr Paul Slovic, a researcher on decision research showed that using background radiation is not very effective in communicating radiation risk.
3. The effective dose due to the most common PA (Posterior-anterior) chest x-ray test is 0.02mSv ( US FDA) The effective dose due to a normal Chest CT procedure is about 7 mSv, thus equal to (7/ 0.02) the dose from 350 chest x-ray tests
4. IRIA stated that modern CT Scanners use “ultra low dose CT” which has radiation comparable to only 5 – 10 chest x-rays. They described ways to reduce the dose further. The software for it is reportedly expensive; the users have no incentive to buy them. The existing practice is not very ideal.
5. X-ray technologists have accomplished acceptable chest CT screening at an overall average effective dose of approximately 2 mSv, a most representative value for low dose CT compared with 7 mSv for a typical standard-dose chest CT examination (Larke et al. US data from 97 Units belonging to 15 models in the National Lung Screening Trial, American J. Roentgenology, Nov 2011 ).
6. In about 3% of the Units in that study, the effective dose was between 3 to 4 mSv. Thus in the extreme case, a low dose chest CT is equal to (4/0.02) 200 chest x-rays.
7. What is the ground reality in India? The officials of the Atomic Energy Regulatory Board (AERB) told me that in over the 5500 or so CT scan units in India, a substantial number does not have "ultra low dose" or low dose features. Low dose techniques need extra care to achieve good diagnostic quality.

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Justification is more important

While doses must be optimum, it is more important to ensure that the diagnostic procedure is justified. Any radiation dose however small is high and unacceptable if the procedure is not clinically indicated. The actual doses are low and in clinically indicated instances the benefits far outweigh the risks. Physicians must discuss risk-benefit issues with patients transparently rather than trivialising them. If physicians earn the trust of patients the problem will vanish. It is difficult but doable.

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Radiation and cancer

Ionising radiation can induce cancer in any organ including the lungs. The radiation sensitivity of each organ is different. The lung is one of the five most radiation-sensitive organs. There is no conclusive scientific evidence of the existence of any threshold dose above which only cancer may be induced in any tissue.

Radiation specialists assume that the effects due to radiation follow the Linear No Threshold (LNT) hypothesis. The effects are linearly dependent on dose without a threshold. Several epidemiological studies have shown excess cancer risk in people exposed to low dose levels, including those due to CT scans. The reports of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) contain good updates of such studies.

Some scientists do not believe in the LNT hypothesis. Some believe that radiation exposure is beneficial. How can we conclude whose view is more scientific? Dr Guleria accepts the theory followed by mainstream scientists and prudently assumes that the carcinogenic effects exist. There is nothing unscientific about it.

The hair-splitting argument is only of academic interest as the magnitude of cancer effects, if any, at diagnostic x-ray doses is negligible or nonexistent compared to the benefits. Do no harm! Carry out medical radiation procedures particularly screening large sections of the populations only if they are justified.

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Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.

Dr K S Parthasarathy is a former Secretary of the Atomic Energy Regulatory Board and a former Raja Ramanna Fellow, Department of Atomic Energy. A Ph. D. from the University of Leeds, UK, he is a medical physicist with a specialisation in radiation safety and regulatory matters. He was a Research Associate at the University of Virginia Medical Centre, Charlottesville, USA. He served the International Atomic Energy Agency as an expert and member in its Technical and Advisory Committees.