Today, I had blood works and appointment with MO (nurse practitioner) three months after starting my second ADT break. I had the last 3 month shot of Eligard on March 2. My PSA was 0.116 on June 2 and today it was 0.104. All this time my Testosterone has been < 20. As long as my Testosterone remains at castrate level getting a shot or not makes no difference. For me, after six or nine months of ADT, Testosterone remains at castrate level for about six months after stopping ADT.
Since I am over 80, it takes long to recover Testosterone. So, my strategy is to stay on break until my PSA becomes detectable (say over 0.25 or so) and then start ADT. In my estimation, my break should end either in December or March next year.