P02.14 Radiotherapy-Associated CT Imaging as a Potential Screening Tool for COVID-19

ABSTRACT

Introduction: COVID-19 is associated with characteristic lung CT findings, such as rounded ground-glass opacities in certain distributions. Diagnosing COVID-19 is a particular concern in oncology care, since cancer patients are a vulnerable population who receive treatment in close proximity to other patients and staff. Radiotherapy patients routinely undergo CT simulation before starting therapy. We hypothesized that simulation CT scans obtained on patients treated during the pandemic would reveal characteristic COVID-19 findings and represent a tool to identify patients with asymptomatic COVID-19. Methods: We reviewed patients undergoing CT simulation during a six-week period (March 1 to April 13, 2020) at a major tertiary cancer center located in an early epicenter of the COVID-19 pandemic in the United States. Most scans were done under free-breathing conditions, with slice thickness ≤3mm and without IV contrast. All scans were reviewed according to the RSNA classification of COVID-19 lung CT findings (“typical,” “indeterminate,” “atypical,” or “negative” for COVID-19 pneumonia) by radiation oncologists who had been trained by a diagnostic radiologist. All “typical” or “indeterminate” scans were considered suspicious and re-reviewed by a board-certified diagnostic radiologist. Radiographic classifications were then compared with available COVID-19 PCR test results. A one-tailed T test was used to compare the rate of positive COVID-19 tests in the radiographically suspicious vs. non-suspicious groups. Results: 414 CT simulation scans that included the lungs were performed on 400 patients during the study period. 119 patients (corresponding to 130 scans, or 31.4%) had COVID-19 PCR test results available. The most common cancer types were breast (37%), lung/thoracic (23%), and spine (21%). On initial review by radiation oncologists, 17 scans (4.1%), were deemed “typical” for COVID-19 pneumonia, 54 (13%) were “indeterminate,” 85 (21%) were “atypical,” and 258 (62.3%) were “negative.” Of the 71 suspicious (typical or indeterminate) scans, 23 had corresponding COVID-19 test results, of which 3 (15.7%) were positive for infection. 107 non-suspicious (atypical or negative) scans had corresponding COVID-19 test results, and 9 were positive (8.4%). This difference in COVID-19 positivity between radiographically suspicious and non-suspicious groups was not statistically significant (p=0.23). Upon re-review by a diagnostic radiologist, 25 (35%) of the suspicious scans were still deemed suspicious while the majority (n=46, or 65%) were deemed “atypical.” Conclusion: Simulation CT scans obtained for radiation treatment planning can be reviewed for signs of COVID-19 pneumonia. About 17% of patients simulated in our metropolitan pandemic epicenter demonstrated findings suspicious for COVID-19 when reviewed by radiation oncologists according to consensus criteria. However, few of these patients proved to have COVID-19 infections based on PCR testing, and there was no significant correlation between radiographically suspicious simulation CT scans and COVID-19 positivity in this study. Analysis was limited by the lack of available COVID-19 test results in many patients. The concordance between radiographic classification by radiation oncologists vs. diagnostic radiologists was also low. These results suggest that routine review of radiotherapy simulation CT scans is of limited value in identifying asymptomatic COVID-19 infection. Keywords COVID-19, radiotherapy, CT