Low-Dose Radiation Therapy for COVID-19 Pneumonia: Comparison of Dosimetry with Conventional AP-PA Fields and Bone Marrow Sparing VMAT

PURPOSE/OBJECTIVE(S): Low-dose radiation therapy (LDRT) to lungs has shown encouraging results in COVID-19 patients in some clinical trials. However, there has been some concern regarding the long-term risk of radiation induced cancer (RIC). Compared to conventional AP-PA field technique, volumetric modulated arc therapy (VMAT) can potentially reduce the dose to marrow and other organs-at-risk (OARs) and thus minimize the risk of cancer. We designed a dosimetry study to study if VMAT can reduce the exposure to marrow and other OARs. MATERIALS/METHODS: We retrieved the CT scan data of 10 patients (aged 40-60 years) who have been already treated for any malignancy in the region of thorax. A dose of 1.0 Gy in single fraction was prescribed to both lungs. All the organs were delineated as per the established guidelines. The dosimetry achieved by the two plans (conventional AP-PA field technique and VMAT) were compared to find the difference. RESULTS: PTV coverage parameters like conformity index (CI) and homogeneity index (HI) were significantly better with VMAT (p value <0.05 for all). As shown in Table 1, Mean dose to most OARs was significantly lower with VMAT (p value <0.05 for all). Mean dose to marrow was significantly lower with VMAT (59.05 vs 81.9 cGy with p value <0.05). CONCLUSION: Compared to conventional technique, VMAT provides better OAR dosimetry for lung irradiation (prescription dose of 1.0 Gy or more) in COVID-19 pneumonia. We therefore suggest, if lung LDRT is used for COVID-19 patients, VMAT as the preferred technique for a prescription dose of ≥1.0 Gy.