@jeffmarc I think it is important that patients understand that the imaging problem mentioned by Dr. Cooperberg is related to the fact that even when an MRI machine is used during a focal treatment procedure, the focal treatment process cannot see all the cancer cells that need to be ablated. Even high quality 3T MRI scans routinely miss "invisible" cancer cells. These are typically 3+3 and 3+4 cell groupings that have not grown dense enough to appear different from healthy cells in an MRI scan. As such, focal treatments nearly always leave some cancer behind because the doctors can't see all the cancer that needs to be destroyed. The cancer left behind may ultimately grow and escape the gland before it can be seen later in a more advanced stage by either MRI imaging or a PSMA PET scan. And thus, it is not a safe situation to say, oh well, we will just do another focal procedure later on if need be. This is why Dr. Cooperberg says focal treatments are best considered to be only an adjunct to active surveillance.

A primary radiation treatment gets around the invisibility issue of some cancer cells because it treats the entire gland and even the wider pelvic region if necessary. Of course, in that approach, healthy tissue is exposed to radiation but the dosages are designed to be something the healthy tissues can tolerate while killing both the seen and unseen cancer cells.