Perhaps it's not as obvious as I thought, but radiation of any sort is certainly to be included in the category of ablation. The advantage of saying "ablation" is that it includes all forms of killing cancer cells or nodules of cancer cells in situ--right where they are, through targeted destruction of all cells in a particular area (and as some have pointed out more or less cells in surrounding areas.
The challenge, of course, is that it won't kill cells that aren't targeted, and it will kill cells that aren't cancerous.
Some of the treatment strategies do not require physical penetration of the body cavity. They suffer from the challenge of getting destructive power to just the right place from a distance.
Other treatment strategies do require getting to the target (like brachytherapy, which embeds tiny pellets of radioactive material) while other strategies require getting close (like HIFU-high intensity focused ultrasound, which typically works from within the urethra.)
Most of the time, ablation is offered as an option to men with cancer that is identified through biopsy as 7=3+4 or less, i.e. intermediate favorable or lower grade cancers. When the cancer is apparently limited to one or two identifiable (and reachable) nodules in the prostate, ablation may slow the progress of the cancer* without requiring an operation removing the prostate and without killing too much else that will be missed. Since the prognosis without any treatment is typically 15-20 years, the thought is that ablation will lead to an even better prognosis (although this gets hard to measure since life gets in the way over these longer time periods.)
*Some would say "stop," but this in my mind is speculative. All of us in this forum once had prostate cancer even though it was undetected ;-).