Low dose lung radiation therapy for pneumonia: an examination of historical dose distributions

The novel coronavirus, SARS-CoV-2, that causes the COVID-19 disease currently has healthcare systems around the world dealing with unprecedented numbers of critically ill patients. One of the primary concerns associated with this illness is acute respiratory distress syndrome (ARDS) and the pneumonia that accompanies it. Historical literature dating back to the 1940s and earlier contains many reports of successful treatment of pneumonias with ionizing radiation. Although these were not randomized controlled trials, they do suggest a potential avenue for further investigation. Technical details in these reports however were limited. In this work we review the literature and identify details including nominal kilovoltage ranges, filtration, and focus-skin distances (FSDs). Using a freely available and benchmarked code, we generated spectra and used these as sources for Monte Carlo simulations using the EGSnrc software package. The approximate sources were projected through a radiologically anthropomorphic phantom to provide detailed dose distributions within a targeted lung volume (approximate right middle lobe). After accounting for the reported exposure levels, mean lung doses fell in a relatively narrow range: 30-80 cGy. Variation in patient dimensions and other details are expected to result in an uncertainty on the order of ± 20%. This result is consistent with the dose range expected to induce anti-inflammatory effects.