These patients had severe pneumonia requiring supplemental oxygen and whose health was visibly deteriorating. They were getting quite close to death.
https://www.forbes.com/sites/jamesconca/2020/06/12/1st-human-trial-successfully-treated-covid-19-using-low-doses-of-radiation/#3de9adc6dc69
Here’s the clinical trial using 1 fraction of low dose radiation therapy (LDRT) that the article refers to:
https://clinicaltrials.gov/ct2/show/NCT04366791