I am writing a case report on a rapidly growing symptomatic brain tumor. The patient had an initial brain MRI which was unremarkable, and no brain tumor identified. after 47 days the patient was symotomatic and mri showed a brain tumor, i have calculated the volume using 3Dslicer software.

Now i want to calculate the estimated doubling time/growth rate of the mass. all the equations i have found need an initial volume which should not be zero because if it is zero the resultant growth rate would be equal to zero or infinity.

I would appreciate your help

thank you,