Since you mention HDR brachytherapy, I assume you mean a radiation oncologist rather than a radiologist. My husband has been treated several times with SBRT by Ryan Phillips, MD PhD, and we have found him not only knowledgeable and experienced, but also easy to talk to and generous with his time. Dr. Phillips' bio on the Mayo Rochester site lists several other types of radiation oncology treatments he performs and specifically mentions HDR brachytherapy for prostate cancer. Hope this helps, and good luck.