How to calculate Increase from baseline

Hi again,
I have a spreadsheet that listed patient #, the tumor size, tumor number, and scan date. I wanted to capture the percent tumor incr/decrease from the baseline. Baseline will be the min date associated with that pt and tumor#. I thought I could use the pivot table to do this but it only gives me the % incr/decr from previous scan date. This is OK with pts who only have 2 scans, but problem with pts with more than 2. Example with pt#018 (sheet1; row 114-116). Spreadsheet attached.
Can someone help me to resolve this problem either with a formula or pivot table. I use Excel 2002 now. Thank you so much in advance!