Reducing inter-operator variability when measuring subcutaneous tumours in mice: An investigation into the effect of inter-operator variability when using callipers or a novel 3D and thermal measurement system

Repeatable tumor measurements are key to accurately assessing tumor growth and treatment efficacy. Our pilot study showed that a novel 3D and thermal imaging system (3D-TI) for measuring subcutaneous rodent tumors significantly reduced inter-operator variability across three in vivo efficacy studies. Here we investigated this reduction in inter-operator variability across a much larger dataset. The dataset of 6,532 paired 3D-TI and caliper inter-operator repeats was obtained from tumor scans and measurements in 27 laboratories across 289 studies, 153 operators, over 20 animal strains and 100 cell lines. Inter-operator variability of the measurement methods was analyzed using coefficient of variation (CV), intra-class correlation (ICC) analysis, and significance testing. Median 3D-TI CV of 0.127 was significantly lower than the median caliper CV of 0.175 (P < 0.00001). The effects of large inter-operator variability at critical points in the study were also investigated. At randomization, changing the operator performing caliper measurements resulted in 59.4% probability that a rodent would be reassigned to a different group. The probability that this would occur when using 3D-TI was significantly lower at 29.2%. In studies where tumor was expected to regress, substituting an operator mid-study resulted in tumor volume increase of approximately 500mm3 when using calipers. The same effect was not reproduced when using 3D-TI. We conclude that 3D-TI offers a significant reduction in inter-operator variability in comparison to calipers, and can improve reproducibility of in vivo studies across a wide range of animal strains and cell lines.