Frequency of surveillance CT scan ordering in patients with stage II/III colorectal cancer.

106 Background: Patients with stage II/III colorectal cancer (CRC) undergo surveillance CT scans to detect early asymptomatic oligometastatic spread, which can be treated with curative intent. However, randomized clinical trials show no difference in 5-year mortality in those that undergo low intensity surveillance (annual) compared a higher intensity strategy (every 6 months). In Ontario, the Program in Evidence-Based Care (PEBC), Ontario Health (Cancer Care Ontario) guidelines recommend surveillance CT scan for patients with stage II/III CRC every 12 months. We aimed to determine the frequency at which clinicians in our Ontario-based hospital system ordered surveillance CT scans for patients with stage II/III CRC. Methods: This single centre retrospective cohort study included all patients that underwent surgical resection for CRC from April 1, 2018 – March 31, 2019 at our academic tertiary care centre in Ontario, Canada. We excluded patients that were followed at an outside hospital, had stage IV disease, had disease recurrence, had a concurrent neoplasm, or did not have CRC. The primary outcome was the proportion of surveillance CT scans completed 10+ months after the previous scan. We also described sociodemographic and medical characteristics of included patients. Follow-up was until August 2023. Results: We included 200 patients. The median age was 62 years (IQR: 52-70), 48% (N=96) were female, the rectum was the most commonly involved disease site (43%, N=86), 38% (N=76) had stage III disease, and 54% (N=107) received adjuvant chemotherapy. A total of 1286 scans were ordered during the study period. Of these, 67% (N=860) were ordered as surveillance. Of these, 18% (n=155) were completed 10 months or longer from the previous scan. The median time interval between surveillance scans was 6.6 months (IQR: 5.9-7.9). Approximately 20% (n=137 of 630) of surveillance scans ordered by general surgeons were completed 10 months or longer from the previous scan, whereas only 9% (n=18 of 205) of scans ordered by medical oncologists were completed 10 months or longer from the previous scan. Less than 1% of surveillance scans (n=3) identified new metastatic disease. Conclusions: The minority of surveillance CT scans ordered in patients with stage II/III CRC in our hospital were timed in concordance with Ontario-based guidelines. Future studies should seek to standardize ordering habits such that they align with best practices.