Greetings,
These days working on s.c. tumors implanted on mice and felt like the process of tumor size measurement has much subjective element in it. I use calipers to measure the longest side of the tumor and the side perpendicular to it to later calculate volume using V = (longest side x shortest side squared)/2. However, whenever I request another person to take the measurements and then compare mine with their measurements there is often big difference. In the end of the day, critical conclusions will be made based on these measurements so I would appreciate your suggestions on how best to make the measurement process more objective. Thanks.
What you are following is standard procedure of measurement of s.c. tumor volume. Values could change with different persons but I guess the relative ratios (absolute volume may differ) should be almost same among groups. It's up to you, how tightly you are measuring a tumor with calipers and maintain same tightness for all tumors. Hope this helps you.
You should always ensure the same person does the measurements for any one study to maintain consistency. Hope this helps.
Have you tried some software for image processing? Take picture of those tumor and picture of some scale as well. Calibrate the scale in image J and do your measurements, apply the same formula. Ask someone to do the same.
Hope this helps
https://imagej.nih.gov/ij/download.html
If you are not satisfied with manual measurements then there is just much more expensive way to do it. For that you would need cells with fluorescent reporter and In Vivo Imager like IVIS SpectrumCT.