Table 5. Fits of experimental data with Eq. (7): estimated parameter values and goodness-of-fit statistics. Columns 1–3 are self-explanatory, column 4 is the chi-square per degree-of-freedom in the fit. While the values of λ are restricted to a rather narrow range, which is in line with the expectation of biological variability between different cell lines, the values of A cover a very wide range. This large variability is justified by the different geometries of the tumours in the list: while spheroids have shapes that never depart too much from the sphere – even when they have very irregular edges – real, vascularized tumours have complex geometries and the total area in contact with blood vessels is very large, hence the large average A value reported for human tumours.

Dataset	λ (μm)	A	χ2/DF
9L spheroids	93.93 ± 0.08	2.75 ± 0.87	1.11
Rat-T1 spheroids	123.56 ± 1.14	20.74 ± 2.27	1.54
MR1 spheroids	90.95 ± 0.001	0.76 ± 0.04	1.20
Human tumors	99.40 ± 5.46	9648.2 ± 0.02	1.02