Response to: Low dose radiation therapy for COVID-19 pneumonia a double-edged sword.

To the Editor

We thank the authors for their response and welcome critical discussion on the potential of LDRT as a treatment for COVID-19 pneumonia. Kefayat and Ghahremani raise several valid points in their letter. Certainly further study on the matter is warranted. Based on historical evidence in the literature and the current pandemic status, the radiation therapy community would be justified in designing both pre-clinical and clinical trials to modern standards to investigate the effectiveness of LDRT against COVID-19 pneumonia using end points such as progression to the need for ventilator support, duration of hospitalization, length of intensive care, and overall mortality rates. We agree that the timing of the irradiation in relation to disease progression is likely to influence treatment outcomes. As such the treatment should be designed to emulate fast-track, palliative treatments with minimal planning and complexity in order to easily adapt to treating large numbers of patients in rapid response to a localized outbreak (e.g., parallel opposed pair chest treatments with standard linear accelerators). This constraint may challenge the authors’ proposition of TBI-type treatment which often requires specialized facilities and increases the plan complexity, although whole lung fields would still irradiate large volumes in order to encompass both lungs simultaneously.

We believe the risks to patients from such studies would be very low. Rates of radiation-induced pneumonitis after whole-lung irradiation for diffuse lung or bone metastasis or prophylactic treatments fall to negligible levels for single fractions of <600 cGy [1]. And while the interplay between radiation dose and viral activity is certainly complex, at the <100 cGy doses proposed, it is unlikely that radiation-induced immunosuppression will have a significant impact on overall disease progression. To date there are no indications that multiple imaging doses exacerbate COVID-19 symptoms. Even in the case of much higher palliative RT doses, consensus statements in the community suggest such treatments may proceed, concerns about population mixing and equipment sterilization notwithstanding [2].