Intersurgeon Agreement in Determining 3 Cm Surgical Margins of Subcutaneous Tumors in Dogs

Objective: To evaluate intersurgeon agreement in performing a 3 cm wide surgical excision for subcutaneous malignancies in dogs.

Study Design: Prospective, blinded, randomized, clinical study.

Animals: Client-owned dogs with subcutaneous tumors undergoing curative-intent, wide surgical excision between April 2019 to March 2020.

Methods: Four surgeons, instructed to perform a 3 cm wide excision, each sequentially indicated their proposed skin incision locations around subcutaneous tumors, without knowledge of the other surgeons' proposed incisions. A tripod-mounted camera and laser positioning system were used to photograph each surgeon's proposed margin length. A random-effects model was used to estimate the standard deviation of margin lengths that would be expected from a random sample of surgeons.

Results: Each of the four surgeons provided 33 independent radial measurements from 11 tumors (six soft tissue sarcomas and five mast cell tumors), for a total of 132 radial measurements. No individual surgeon consistently proposed longer or shorter margin incision locations. The prediction interval for a future margin measurement was 6 mm, implying that the 95% confidence interval of an individual surgeon's margin length would be within ±6 mm of the mean margin length from a random sample of surgeons.

Conclusion: Ninety-five percent of surgeons would be expected to deliver a surgical dose between 2.4-3.6 cm, for a theoretically uniform surgical dose of 3 cm wide margins.

Clinical Significance: Surgical doses are likely to vary at clinically relevant levels among surgeons, complicating design and interpretation of studies attempting to identify an ideal surgical dose.