Hi, Debbie
as I understand it, 3 months is the typical minumum wait for a planned PET, but I have seen references to 2-6 months in some of the literature I have read. My husband's doctors wouldn't specify the date until about a month before he had the scan.

CG to husband - SCC Tonsil T1N2M0 HPV+ Never Smoker
First symptoms 7/2010, DX 12/2010
TX 40 IRMT (1.8 gy) + 10 Cetuximab
PET Scans 6/2011 + 3/2012 clear, 5 year physical exam clear; chest CT's clear of cancer. On thyroid pills. Life is good.