Low-dose radiotherapy for COVID-19 pneumonia treatment: case report, procedure, and literature review

Radiotherapy for non-cancer diseases: benefits and long-term risks

PURPOSE

The discovery of X-rays was followed by a variety of attempts to treat infectious diseases and various other non-cancer diseases with ionizing radiation, in addition to cancer. There has been a recent resurgence of interest in the use of such radiotherapy for non-cancer diseases. Non-cancer diseases for which use of radiotherapy has currently been proposed include refractory ventricular tachycardia, neurodegenerative diseases (e.g. Alzheimer's disease and dementia), and Coronavirus Disease 2019 (COVID-19) pneumonia, all with ongoing clinical studies that deliver radiation doses of 0.5-25 Gy in a single fraction or in multiple daily fractions. In addition to such non-cancer effects, historical indications predominantly used in some countries (e.g. Germany) include osteoarthritis and degenerative diseases of the bones and joints. This narrative review gives an overview of the biological rationale and ongoing preclinical and clinical studies for radiotherapy proposed for various non-cancer diseases, discusses the plausibility of the proposed biological rationale, and considers the long-term radiation risks of cancer and non-cancer diseases.

CONCLUSIONS

A growing body of evidence has suggested that radiation represents a double-edged sword, not only for cancer, but also for non-cancer diseases. At present, clinical evidence has shown some beneficial effects of radiotherapy for ventricular tachycardia, but there is little or no such evidence of radiotherapy for other newly proposed non-cancer diseases (e.g. Alzheimer's disease, COVID-19 pneumonia). Patients with ventricular tachycardia and COVID-19 pneumonia have thus far been treated with radiotherapy when they are an urgent life threat with no efficient alternative treatment, but some survivors may encounter a paradoxical situation where patients were rescued by radiotherapy but then get harmed by radiotherapy. Further studies are needed to justify the clinical use of radiotherapy for non-cancer diseases, and optimize dose to diseased tissue while minimizing dose to healthy tissue.

Efficacy of low-dose lung radiotherapy in the management of COVID-19 patients: a randomised, open-label study

OBJECTIVE

Evaluate role of low-dose radiotherapy (LDRT) in COVID-19 pneumonia.

METHODS

Sixty-five patients 40 years or older tested positive for COVID-19 reverse transcriptase-polymerase chain reaction with mild to moderate acute respiratory distress syndrome (ARDS), were randomised 1:1, from 4 June 2021, to either best standard of care (control arm) according to the Indian Council of Medical Research guidelines or a single dose of LDRT (LDRT-0.5Gy) to both lungs along with best standard of care (experimental arm). The primary outcome was either progression to severe disease (PaO2/FiO2 ratio <100 mmHg) within 28 days of randomisation or all-cause mortality at 28 days. If the primary outcome could have been prevented, it was considered "favourable"; if not, it was considered "unfavourable."

RESULTS

Thirty-three patients were allocated to experimental arm, 32 to control arm. An intention to treat analysis was performed. Unfavourable outcome was seen in 5 (15.2%) patients in experimental arm, vs , 12 (37.5%) patients in control arm, odds of an unfavourable outcome in experimental arm were 0.3, 95% CI 0.09-0.97; two-sided p = 0.04. Four and five patients died in experimental and control arm, respectively. No radiation-induced toxicity was observed.

CONCLUSION

LDRT reduced the number of patients with unfavourable outcome at 28 days.

ADVANCES IN KNOWLEDGE

One of the few randomised studies showing reduced unfavourable outcome in mild to moderate ARDS COVID-19 patients receiving LDRT.CTRI/2021/06/034001, Clinical Trials Registry - India (ICMR-NIMS).

COVID-19 and tuberculosis coinfection: An overview of case reports/case series and meta-analysis of prevalence studies

Background and aim

Coronavirus disease 2019 (COVID-19) coinfection with other respiratory pathogens poses a serious concern that can complicate diagnosis, treatment, and prognosis. Since COVID-19 and tuberculosis are both severe respiratory infections, their symptoms may overlap and even increase mortality in case of coinfection. The current study aimed to investigate the coinfection of tuberculosis and COVID-19 worldwide through a systematic review and meta-analysis.

Methods

A systematic literature search based on the Systematic Reviews and Meta-Analyses" (PRISMA) was performed on September 28, 2021, for original research articles published in PubMed, Web of Science, and Embase databases from December 2019 to September 2021 using relevant keywords. Data analysis was performed using Stata 14 software.

Results

The final evaluation included 18 prevalence studies with 5843 patients with COVID-19 and 101 patients with COVID-19 and Mycobacterium tuberculosis (M. tuberculosis). The prevalence of tuberculosis infection was 1.1% in patients with confirmed COVID-19. This coinfection among patients with COVID-19 was 3.6% in Africa, 1.5% in Asia, and 1.1% in America. Eighteen case reports and 57 case series were also selected. Eighty-nine adults (67 men and 22 women) with a mean age of 45.14 years had concurrent infections with tuberculosis. The most common clinical manifestations were fever, cough, and weight loss. A total of 20.83% of evaluated patients died, whereas 65.62% recovered. Lopinavir/ritonavir was the most widely used antiviral drug for 10.41% of patients.

Conclusion

COVID-19 has a low prevalence of tuberculosis coinfection, but it remains a critical issue, especially for high-risk individuals. The exact rate of simultaneous tuberculosis in COVID-19 patients could not be reported since we didn't have access to all data worldwide. Therefore, further studies in this field are strongly recommended.

Low-Dose Whole Lung Irradiation for Treatment of COVID-19 Pneumonia: A Systematic Review and Meta-Analysis

PURPOSE

Studies dating back to a century ago have reported using low-dose radiation therapy for the treatment of viral and bacterial pneumonia. In the modern era, since the COVID-19 pandemic began, several groups worldwide have researched the applicability of whole lung irradiation (WLI) for the treatment of COVID-19. We aimed to bring together the results of these experimental studies.

METHODS AND MATERIALS

We performed a systematic review and meta-analysis searching PubMed and Scopus databases for clinical trials incorporating WLI for the treatment of patients with COVID-19. Required data were extracted from each study. Using the random-effects model, the overall pooled day 28 survival rate, survival hazard ratio, and intubation-free days within 15 days after WLI were calculated, and forest plots were produced.

RESULTS

Ten studies were identified, and eventually, 5 were included for meta-analysis. The overall survival hazard ratio was calculated to be 0.85 (0.46-1.57). The pooled mean difference of intubation-free days within 15 days after WLI was 1.87, favoring the WLI group (95% confidence interval, -0.02 to 3.76). The overall day 28 survival rate of patients receiving WLI for the 9 studies with adequate follow-up data was 74% (95% confidence interval, 61-87). Except for 2 studies, the other 8 studies were assessed to have moderate to high risk of bias, and there were many differences among the designs of the studies, included patients, primary endpoints, outcome measurement methods, and reporting of the results.

CONCLUSIONS

Despite a mild improvement in intubation-free days, WLI had no significant effect on patients' overall survival. Currently, we cannot recommend routine use of WLI for the treatment of patients with moderate-to-severe COVID-19.

Covid-19 and radiotherapy: a systematic review after 2 years of pandemic

Introduction

Following the Covid-19 pandemic spread, changes in clinical practice were necessary to limit the pandemic diffusion. Also, oncological practice has undergone changes with radiotherapy (RT) treatments playing a key role.Although several experiences have been published, the aim of this review is to summarize the current evidence after 2 years of pandemic to provide useful conclusions for clinicians.

Methods

A Pubmed/MEDLINE and Embase systematic review was conducted. The search strategy was "Covid AND Radiotherapy" and only original articles in the English language were considered.

Results

A total of 2.733 papers were obtained using the mentioned search strategy. After the complete selection process, a total of 281 papers were considered eligible for the analysis of the results.

Discussion

RT has played a key role in Covid-19 pandemic as it has proved more resilient than surgery and chemotherapy. The impact of the accelerated use of hypofractionated RT and telemedicine will make these strategies central also in the post-pandemic period.

Effect of Low-Dose Radiotherapy on the Circulating Levels of Paraoxonase-1-Related Variables and Markers of Inflammation in Patients with COVID-19 Pneumonia

The aim of our study was to investigate the changes produced by low-dose radiotherapy (LDRT) in the circulating levels of the antioxidant enzyme paraoxonase-1 (PON1) and inflammatory markers in patients with COVID-19 pneumonia treated with LDRT and their interactions with clinical and radiological changes. Data were collected from the IPACOVID prospective clinical trial (NCT04380818). The study included 30 patients treated with a whole-lung dose of 0.5 Gy. Clinical follow-up, as well as PON1-related variables, cytokines, and radiological parameters were analyzed before LDRT, at 24 h, and 1 week after treatment. Twenty-five patients (83.3%) survived 1 week after LDRT. Respiratory function and radiological images improved in survivors. Twenty-four hours after LDRT, PON1 concentration significantly decreased, while transforming growth factor beta 1 (TGF-β1) increased with respect to baseline. One week after LDRT, patients had increased PON1 activities and lower PON1 and TGF-β1 concentrations compared with 24 h after LDRT, PON1 specific activity increased, lactate dehydrogenase (LDH), and C-reactive protein (CRP) decreased, and CD4+ and CD8+ cells increased after one week. Our results highlight the benefit of LDRT in patients with COVID-19 pneumonia and it might be mediated, at least in part, by an increase in serum PON1 activity at one week and an increase in TGF-β1 concentrations at 24 h.

Low-dose radiotherapy for COVID-19 pneumonia and cancer: summary of a recent symposium and future perspectives

The lessons learned from the Coronavirus Disease 2019 (COVID-19) pandemic are numerous. Low dose radiotherapy (LDRT) was used in the pre-antibiotic era as treatment for bacterially/virally associated pneumonia. Motivated in part by these historic clinical and radiobiological data, LDRT for treatment of COVID-19-associated pneumonia was proposed in early 2020. Although there is a large body of epidemiological and experimental data pointing to effects such as cancer at low doses, there is some evidence of beneficial health effects at low doses. It has been hypothesized that low dose radiation could be combined with immune checkpoint therapy to treat cancer. We shall review here some of these old radiobiological and epidemiological data, as well as the newer data on low dose radiation and stimulated immune response and other relevant emerging data. The paper includes a summary of several oral presentations given in a Symposium on "Low dose RT for COVID and other inflammatory diseases" as part of the 67th Annual Meeting of the Radiation Research Society, held virtually 3-6 October 2021.

Effectiveness of low-dose radiation therapy in COVID-19 patients globally: A systematic review

Background: Novel Corona Virus Disease 2019 (COVID-19) can affect multiple organs, including the lungs, resulting in pneumonia. Apart from steroids, other anti-COVID drugs that have been studied appear to have little or no effect on COVID-19 pneumonia. There is a well-known history of inflammatory disease, including pneumonia, treated with low-dose radiation therapy (LDRT). It reduces the production of proinflammatory cytokines, Interleukin-1a (IL-1a), and leukocyte recruitment.   Methods: A comprehensive literature search was conducted using PubMed, Scopus, Embase, CINAHL, and Google Scholar, with keywords such as "radiotherapy," "low-dose radiation therapy," "low-dose irradiation," "covid-19 pneumonia," "SARS-CoV-2 pneumonia," and "covid pneumonia." with additional filters for human studies and customized articles in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. We reviewed randomized controlled trials, quasi-experimental studies, cohort, case-control, and cross-sectional studies with a clearly defined intervention, including low-dose radiotherapy alone or in combination with any therapy to treat COVID-19 pneumonia from December 2019 to May 2021. Patients receiving standard or high-dose radiotherapy, including for other diseases, were excluded. Zotero software was used to collect and organize research from various databases, remove duplicates, extract relevant data, and record decisions. Participants' demographics and baseline status were obtained from the full-text articles along with the intervention's outcome/effect on patient status.  Results: Four studies with 61 participants that met the inclusion criteria were included. One was a double-blind randomized controlled trial, one a non-randomized trial, while the other two were single-arm clinical trials. Low-dose radiation therapy did not show any significant improvement in COVID-19 patients.  Conclusion: Only two studies included in this review demonstrated an improvement in inflammatory markers; however, patients were also given steroids or other drugs. Therefore, the confounding effects must be considered before drawing conclusions. This systematic review does not support mortality benefit, clinical course improvement, or imaging changes with LDRT.

A model of infection and immune response to low dose radiation

PURPOSE

Low dose radiation therapy (LDRT) using doses in the range of 30-150 cGy has been proposed as a means of mitigating the pneumonia associated with COVID-19. However, preliminary results from ongoing clinical trials have been mixed. The aim of this work is to develop a mathematical model of the viral infection and associated systemic inflammation in a patient based on the time evolution of the viral load. The model further proposes an immunomodulatory response to LDRT based on available data. Inflammation kinetics are then explored and compared to clinical results.

METHODS

The time evolution of a viral infection, inflammatory signaling factors, and inflammatory response are modeled by a set of coupled differential equations. Adjustable parameters are taken from the literature where available and otherwise iteratively adjusted to fit relevant data. Simple functions modeling both the suppression of pro-inflammatory signal factors and the enhancement of anti-inflammatory factors in response to low doses of radiation are developed. The inflammation response is benchmarked against C-reactive protein (CRP) levels measured for cohorts of patients with severe COVID-19.

RESULTS

The model fit the time-evolution of viral load data, cytokine data, and inflammation (CRP) data. When LDRT was applied early, the model predicted a reduction in peak inflammation consistent with the difference between the non-surviving and surviving cohorts. This reduction of peak inflammation diminished as the application of LDRT was delayed.

CONCLUSION

The model tracks the available data on viral load, cytokine levels, and inflammatory biomarkers well. An LDRT effect is large enough in principle to provide a life-saving immunomodulatory effect, though patients treated with LDRT already near the peak of their inflammation trajectory are unlikely to see drastic reductions in that peak. This result potentially explains some discrepancies in the preliminary clinical trial data.

Low-dose whole-lung irradiation in severe COVID-19 pneumonia: a controlled clinical trial

INTRODUCTION

The COVID-19 pandemic has caused significant morbidity and mortality thus far. Considering the historical uses of high-voltage X-ray beams for unresolvable pneumonia, we aimed to assess whether low-dose whole-lung irradiation (WLI) could provide any benefits for patients with refractory COVID-19 pneumonia.

METHODS

Eleven patients with refractory COVID-19 pneumonia were treated with WLI to a total dose of 1 Gy and compared to 11 patients in a matched control group from June to November 2020. The study's primary endpoint was improvement of chest X-ray severity score (CXRS), followed by changes in mean oxygen (O2) saturation and 28-day mortality as secondary endpoints.

RESULTS

The final CXRS was significantly lower in the WLI group (8.7 ± 2.5) compared to the control group (12.3 ± 3.3) (P: 0.016). Change of CXRS from the first to the last chest X-ray was -2.2 ± 3.1 for the WLI group and 0.7 ± 3.9 for the control group, which showed a trend for lower CXRS in the WLI group (U = 30, p: 0.085). Mean O2 saturation showed insignificant improvement in the first 24 hours after radiotherapy (mean difference: 2.5 ± 4.1, Z=-1.6, P value: 0.11). Overall survival after 28 days was 32% in the WLI group and 11% in the control group (P: 0.48). The reason for death in many patients was not merely respiratory failure, but also other adverse situations like pneumothorax, cardiogenic shock and pulmonary thromboembolism.

CONCLUSIONS

Low-dose WLI could improve the CXR severity score and O2 saturation in severely ill COVID-19 patients, but larger studies are required to determine its impact on mortality.

Could pulmonary low-dose radiation therapy be an alternative treatment for patients with COVID-19 pneumonia? Preliminary results of a multicenter SEOR-GICOR nonrandomized prospective trial (IPACOVID trial)

PURPOSE

To evaluate the efficacy and safety of lung low-dose radiation therapy (LD-RT) for pneumonia in patients with coronavirus disease 2019 (COVID-19).

MATERIALS AND METHODS

Inclusion criteria comprised patients with COVID-19-related moderate-severe pneumonia warranting hospitalization with supplemental O2 and not candidates for admission to the intensive care unit because of comorbidities or general status. All patients received single lung dose of 0.5 Gy. Respiratory and systemic inflammatory parameters were evaluated before irradiation, at 24 h and 1 week after LD-RT. Primary endpoint was increased in the ratio of arterial oxygen partial pressure (PaO2) or the pulse oximetry saturation (SpO2) to fractional inspired oxygen (FiO2) ratio of at least 20% at 24 h with respect to the preirradiation value.

RESULTS

Between June and November 2020, 36 patients with COVID-19 pneumonia and a mean age of 84 years were enrolled. Seventeen were women and 19 were men and all of them had comorbidities. All patients had bilateral pulmonary infiltrates on chest X‑ray. All patients received dexamethasone treatment. Mean SpO2 pretreatment value was 94.28% and the SpO2/FiO2 ratio varied from 255 mm Hg to 283 mm Hg at 24 h and to 381 mm Hg at 1 week, respectively. In those who survived (23/36, 64%), a significant improvement was observed in the percentage of lung involvement in the CT scan at 1 week after LD-RT. No adverse effects related to radiation treatment have been reported.

CONCLUSIONS

LD-RT appears to be a feasible and safe option in a population with COVID-19 bilateral interstitial pneumonia in the presence of significant comorbidities.

Low-dose radiation therapy for COVID-19 pneumonia: a pilot study

Objectives:

The World Health Organization (WHO) has declared coronavirus disease 2019 (COVID-19) as pandemic in March 2020. Currently there is no specific effective treatment for COVID-19. The major cause of death in COVID-19 is severe pneumonia leading to respiratory failure. Radiation in low doses (<100 cGy) has been known for its anti-inflammatory effect and therefore, low dose radiation therapy (LDRT) to lungs can potentially mitigate the severity of pneumonia and reduce mortality. We conducted a pilot trial to study the feasibility and clinical efficacy of LDRT to lungs in the management of patients with COVID-19.

Methods:

From June to Aug 2020, we enrolled 10 patients with COVID-19 having moderate to severe risk disease [National Early Warning Score (NEWS) of ≥5]. Patients were treated as per the standard COVID-19 management guidelines along with LDRT to both lungs with a dose of 70cGy in single fraction. Response assessment was done based on the clinical parameters using the NEWS.

Results:

All patients completed the prescribed treatment. Nine patients had complete clinical recovery mostly within a period ranging from 3 to 7 days. One patient, who was a known hypertensive, showed clinical deterioration and died 24 days after LDRT. No patients showed the signs of acute radiation toxicity.

Conclusion:

The results of our pilot study suggest that LDRT is feasible in COVID-19 patients having moderate to severe disease. Its clinical efficacy may be tested by conducting randomized controlled trials.

Advances in knowledge:

LDRT has shown promising results in COVID-19 pneumonia and should be researched further through randomized controlled trials.

COVID-19 and low-dose radiation therapy

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative pathogen of the coronavirus disease 2019 (COVID-19), has caused more than 179 million infections and 3.8 million deaths worldwide. Global health authorities working on the COVID-19 outbreak continue to explore methods to reduce the rate of its transmission to healthy individuals. Treatment protocols thus far have focused on social distancing and masking, treatment with antivirals early in infection, and steroids to reduce the inflammatory response. An alternative approach is therapy with low dose radiation (LDR), which has several advantages compared to the current drugs and medicines. To date more than 10 case reports and pilot clinical trial preliminary outcome are available from different countries. These reports cover a wide range of patient conditions and LDR treatment strategies. Although one report showed the failure to observe the improvement of COVID-19 patients after LDR therapy, the majority showed some clinical improvement, and demonstrated the safety of LDR for COVID-19 patients, particularly with 0.5 Gy. This review aims to summarize the potential rationales and mechanisms of LDR therapy for COVID-19 patients, and its current clinical status and potential use.

Low-Dose Radiation Therapy for COVID-19: A Systematic Review

The ongoing COVID-19 pandemic is of great concern for the whole world, and finding an effective treatment for the disease caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is, therefore, a global race. In particular, treatment options for elderly patients and patients with genetic risk factors with COVID-19-associated pneumonia are limited, and many patients die. Low-dose radiotherapy (LDRT) of lungs was used to treat pneumonia many decades ago. Since the first report on the potential efficacy of LDRT for COVID-19-associated pneumonia was published on 1 April, 2020, tens of papers have addressed the importance of this treatment. Moreover, the findings of less than 10 clinical trials conducted to date are now available. We performed a detailed search of PubMed/MEDLINE, Web of Science, Google Scholar, and Scopus and selected the nine most relevant articles. A review of these articles was conducted. The available data indicate that in oxygen-dependent elderly patients with COVID-19-associated pneumonia, whole-lung radiation at doses of 0.5–1.5 Gy can lead to accelerated recovery and progress in clinical status, encephalopathy, and radiographic consolidation without any detectable acute toxicity. Although data collected so far show that LDRT could be introduced as a treatment with promising efficacy, due to limitations such as lack of randomization in most studies, we need further large-scale randomized studies, especially for elderly patients who are at greater risk of mortality due to COVID-19. However, more preclinical work and clinical trials are needed before any clear conclusion can be made.

Effectiveness of low-dose radiation therapy to improve mortality of COVID-19

INTRODUCTION

Performing low-dose radiation therapy (LDRT) is a new approach to treat pneumonia resulting from COVID-19 disease. This paper aims to evaluate the effectiveness of LDRT in treating COVID-19 patients.

METHODS

Medline was searched for "low-dose" and "radiation therapy" and "COVID-19" and "pneumonia" and "inflammation", to retrieve papers that published on low-dose radiation therapy to improve mortality of COVID-19 patients. Only clinical investigations that included original and case report papers were selected for this paper.

RESULTS

The completed clinical trials that have performed LDRT to treat COVID-19 showed that the effectiveness of LDRT in treating COVID-19 was up to 90%.

CONCLUSION

The vast majority of primary and secondary outcomes of clinical trial investigations regarding LDRT in treating COVID-19 found that LDRT can be considered a feasible treatment to improve mortality of COVID-19 patients.

Low dose ionizing radiation and the immune response: what is the role of non-targeted effects?

OBJECTIVES

This review aims to trace the historical narrative surrounding the low dose effects of radiation on the immune system and how our understanding has changed from the beginning of the 20th century to now. The particular focus is on the non-targeted effects (NTEs) of low dose ionizing radiation (LDIR) which are effects that occur when irradiated cells emit signals that cause effects in the nearby or distant non-irradiated cells known as radiation induced bystander effect (RIBE). Moreover, radiation induced genomic instability (RIGI) and abscopal effect (AE) also regarded as NTE. This was prompted by our recent discovery that ultraviolet A (UVA) photons are emitted by the irradiated cells and that these photons can trigger NTE such as the RIBE in unirradiated recipients of these photons. Given the well-known association between UV radiation and the immune response, where these biophotons may pose as bystander signals potentiating processes in deep tissues as a consequence of LDIR, it is timely to review the field with a fresh lens. Various pathways and immune components that contribute to the beneficial and adverse types of modulation induced by LDR will also be revisited.

CONCLUSION

There is limited evidence for LDIR induced immune effects by way of a non-targeted mechanism in biological tissue. The literature examining low to medium dose effects of ionizing radiation on the immune system and its components is complex and controversial. Early work was compromised by lack of good dosimetry while later work mainly looks at the involvement of immune response in radiotherapy. There is a lack of research in the LDIR/NTE field focusing on immune response although bone marrow stem cells and lineages were critical in the identification and characterization of NTE where effects like RIGI and RIBE were heavily researched. This may be in part, a result of the difficulty of isolating NTE in whole organisms which are essential for good immune response studies. Models involving inter organism transmission of NTE are a promising route to overcome these issues.

Low dose lung radiotherapy for COVID-19 pneumonia: A potential treatment

The covid-19 pandemic has been affecting many countries across the world and lost precious lives. Most patients suffer from respiratory disease which progresses to the severe acute respiratory syndrome, termed as SARS-CoV-2 pneumonia. A systemic inflammatory response occurs in SARS-CoV-2 pneumonia severely ill patients, The inflammation process if uncontrolled has a detrimental effect, and the release of cytokines play an important role leading to lung fibrosis. Radiation therapy used in low doses has an anti-inflammatory and immunomodulatory effect. Its low cost, wider availability, and decreased risk of acute side effects can reduce the burden on the health care system.

[Low dose radiotherapy for COVID-19 pneumopathy: Biological rationale and literature review]

La pandémie de coronavirus disease 2019 (covid-19) due au severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2) évolue depuis un peu plus d’un an. Si la majorité des formes est bénigne, des pneumopathies graves, voire mortelles, se développent chez certains patients plus à risque. De nombreuses pistes thérapeutiques ont été explorées avec cependant trop peu d’impact sur la mortalité. C’est dans ce contexte que Kirkby et Mackenzie ont rappelé en avril 2020 les propriétés anti-inflammatoires de la radiothérapie de faible dose (délivrant moins de 1 Gy) et son utilisation dans le traitement des pneumopathies bactériennes et virales avant l’ère des antibiotiques. En effet, de larges données in vitro et in vivo ont démontré le rationnel biologique à l’origine de la diminution de l’inflammation après une radiothérapie de faible dose dans de nombreuses pathologies. Depuis un an, trois essais cliniques de phase I/II ont été publiés ainsi qu’un essai randomisé, rapportant la faisabilité et l’amélioration clinique et biologique d’un traitement bipulmonaire par une dose 0,5 à 1 Gy. Treize autres études, dont une phase III randomisée, sont en cours dans le monde. Celles-ci pourront permettre de mieux apprécier les effets de la radiothérapie de faible dose pour la pneumonie à SARS-CoV-2. Cette revue s’attache à rappeler le rationnel biologique de l’utilisation de la radiothérapie de faible dose dans les pneumopathies, et de rapporter les résultats des essais publiés ou en cours sur son utilisation spécifique pour la pneumopathie à SARS-CoV-2.

Low Doses of Radiation Increase the Immunosuppressive Profile of Lung Macrophages During Viral Infection and Pneumonia

Purpose

Severe pneumonia and acute respiratory distress syndrome (ARDS) have been described in patients with severe coronavirus disease 2019 (COVID-19). Recently, early clinical data reported the feasibility of low doses of radiation therapy (RT) in the treatment of ARDS in patients with severe COVID-19. However, the involved mechanisms remained unknown.

Methods and Materials

Here, we used airways-instilled lipopolysaccharide (LPS) and influenza virus (H1N1) as murine models of pneumonia, and toll-like receptor (TLR)-3 stimulation in human lung macrophages.

Results

Low doses of RT (0.5-1 Gray) decreased LPS-induced pneumonia, and increased the percentage of nerve- and airway-associated macrophages producing interleukin (IL) 10. During H1N1 viral infection, we observed decreased lung tissue damage and immune cell infiltration in irradiated animals. Low doses of RT increased IL-10 production by infiltrating immune cells into the lung. Irradiation of TLR-3 ligand-stimulated human lung macrophages ex vivo increased IL-10 secretion and decreased interferon γ production in the culture supernatant. The percentage of human lung macrophages producing IL-6 was also decreased.

Conclusions

Our data highlight a mechanism by which low doses of RT regulate lung inflammation and skew lung macrophages toward an anti-inflammatory profile. These data provide a preclinical mechanistic support to clinical trials evaluating low doses of RT, such as COVID-19-induced ARDS.