S. Melemenidis1, L. A. Soto1, J. B. Schulz1, M. R. Ashraf1, A. El Kaffas1, B. W. Loo Jr2, and E. E. Graves1; 1Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, 2Department of Radiation Oncology, Stanford University, Stanford, CA
Purpose/Objective(s): Longitudinal monitoring of tumor volume is a fundamental component of preclinical biomedical research. We explored the use of inexpensive portable ultrasound (US) probes as a viable, cost-and time-efficient alternative to the standard caliper-based volume measurements in laboratory settings, aiming to compare these methods and establish a more precise measurement technique. Materials/
Methods: 5 BALB/c and 5 C57Bl6/J mice were shaved and injected subcutaneously with 105 colon (CT26) or lung (LLC1) carcinoma cells on the flank. At day 14, tumor length and width (LxW) were measured with either calipers or a portable handheld US probe (frequency: 8-20MHz, maximum depth: 4cm), which provided 2D images across the LxW. Tumors were subsequently excised and imaged with cone-beam computed tomography (CBCT) to obtain a gold-standard volume measurement. The widely-used ellipsoid volume formula was applied to US- and caliper-derived LxW as well as to LxW and the US-derived tumor depth (D) measured from the orthogonal cross-section. In addition to these methods, we developed a novel algorithm designed to estimate tumor volumes from regions of interest (ROIs) defined on two orthogonal US cross sections. Results: The CBCT volumes ranged from 30-170mm3, with an average volume of 82.8 ± 49.6mm3. The average of the caliper-derived volume was 206% ± 76% of the reference volume, the average US-derived volume estimated from the caliper formula was 106% ± 41%, and the average volume from the US-derived LxWxD applied to the traditional ellipsoid formula was 90% ± 34%. The average from the ROI-derived volumes from the 2 orthogonal US views was 94% ± 12%. Conclusion: Our study demonstrates the feasibility of rapid US-based measurement of tumor volumes that offers improved accuracy relative to standard caliper-based approaches. The adoption of a portable handheld US probe for acquiring width, length, and depth measurements enhances the precision of the average tumor volume estimations by ~100% when applied to the ellipsoid formula. The calculated volumes from the ROIs using two orthogonal US views closely align with this improved performance and exhibit the least variability across tumors, suggesting that this approach is better suited for tumors with irregular shapes. Although image collection with US was initially two times lengthier than caliper measurements, we anticipate that with increased user proficiency, the time required could decrease further.
