We present a patient with recurrent non-small cell lung cancer in whom asymptomatic COVID-19 was detected after abnormal volumetric CT image-guidance as part of routine set-up and delivery of curative stereotactic ablative radiotherapy.
In January 2020, a 63-year-old woman was diagnosed with a left upper lobe recurrence of pulmonary adenocarcinoma. The patient was referred for stereotactic ablative radiotherapy (SABR) and enrolled on a phase II protocol investigating the addition of nivolumab to SABR in the definitive management of non-small cell lung cancer (NCT03110978).
On arrival for her first SABR treatment, the patient was screened per COVID-19 pandemic policies and deemed low-risk for infection (no new respiratory symptoms, normal body temperature, no recent travel). As per standard SABR protocol, volumetric imaging of the patient's thorax was obtained via CT-on-rails (CTOR) for patient set-up and tumor localization. Comparison with her initial CT-simulation scan (20 days prior) revealed interval development of new multifocal ground glass opacities of the lungs (Figure 1 ). Treatment was held and within 12 hours SARS-Cov2 nasopharyngeal swab RT-PCR resulted positive. The patient was advised on strict home quarantine and return precautions; all personnel involved were rapidly notified, screened, and cleared accordingly. The patient's radiation treatments were deferred until subsequent negative test, as per departmental policy for all patients with suspected or confirmed COVID-19. The patient remained asymptomatic, though her household contacts subsequently became ill with confirmed COVID-19.
As the COVID-19 pandemic spreads, healthcare systems must quickly adapt to minimize the global impact. Of the 429,052 confirmed cases within the United States, many have been linked to asymptomatic community spread. 2 Early recognition of infected patients could streamline isolation protocols and thus mitigate adverse outcomes of COVID-19, particularly among our vulnerable oncologic patient population; 3 however, standard screening and testing measures have been insufficient due to limitations in access and speed. Characteristic radiographic findings have been reported on diagnostic chest CTs of patients with COVID-19 infection. Typical CT findings include bilateral parenchymal ground glass and consolidative pulmonary opacities with frequent rounded morphology and peripheral lung distribution (Table 1) . 4 Data support the utility of chest CTs for primary detection among epidemic areas; and in some cases, chest CT has been shown to be more sensitive than RT-PCR, particularly in the earliest (likely asymptomatic) phases of infection. 4 Suppli et al. report on a similar case with detectable cone beam CT (CBCT) abnormalities 36 hours in advance of clinical COVID-19 symptoms and diagnosis. 5 In our case the patient remained asymptomaticincreasing the risk of potential silent spread in our department. Note the superior image resolution of CTOR (in the current report) versus CBCT on comparison. Due to streak artifacts, subtle ground glass opacities are difficult to detect on CBCT, particularly when obtained free breathing, although CBCT benefits from ubiquity across Radiation Oncology departments. However, both cases advocate for staff in radiotherapy departments to remain vigilant for unexpected ground glass changes on both initial CT-Simulation and daily CT imageguidance, which can serve as a rapid assessment tool in the COVID-19 pandemic, permitting early isolation procedures and providing valuable clinical input towards diagnosis while awaiting RT-PCR confirmation. Figure 1 . Initial CT simulation images for treatment planning (left), compared to CT image-guidance prior to the first fraction of stereotactic ablative radiotherapy, scheduled 20 days later (right).