Thanks for the links PaulW, much appreciated.
The most recent research I've stumbled upon states that proton therapy better spares healthy tissue from radiation than does conventional photon therapy. An excerpt from this 2017 Nature
abstract states the same:https://www.nature.com/nrclinonc/journal/v14/n8/full/nrclinonc.2017.30.html
Also, this article http://www.nature.com/news/three-ways-to-make-proton-therapy-affordable-1.22660?WT.mc_id=FBK_NatureNews&sf116491847=1
reinforces the notion that access to the best proton therapy machines are hindered due to cost. Lower cost versions may be forthcoming. The article also shows in simplistic fashion the different ways conventional radiation and protons pass through the body, and states that protons can be stopped at the depth of the tumor and then released.
I met with Dr. Loeffler, MGH raditaion oncologist, yesterday to talk about whether I might be ready for treatment of any kind. (His advice was to continue to wait and watch -- while that was encouraging, I do intend to ask other docs relatively soon due to my symptoms and the MRI he had was 6 mos old). In addition, I asked about the 3 mm range of uncertainty regarding the release of the energy into the tumor, and the notion that 120% of the energy is also released at the periphery. He said the 3 mm discrepancy was false information. He seemed to concur with an increase at the periphery though at perhaps 5% more rather than 20% and that effective controls are in place. He didn't go into much detail on the issue, nor did I ask as his opinion about my case was such that it would be best for me to continue to watch and wait. And, his response does not square with the PP presentation that PaulW sent. Still, the PP was 5 years ago and some changes may have occurred since then that would alter the results. In addition, due to the relatively smallish size of my AN (10 mm as of 6 mos ago) Dr. Loeffler said either radiation treatment (photon or proton) would be fine. This may imply some relevance to PaulW's comments that proton beam therapy is better suited to larger (> 2 cm?) tumors. I really don't know, nor am I a physicist, oncologist or any other medical care professional; just a curious individual dealing with an unwanted condition, like most people here. I do like the notion that proton beam therapy minimizes radiation to healthy tissue. As time goes on, we will glean even more.
Dr. Loeffler is currently chair of the department where Dr. Paganetti (author of the PP) works; both teach at the same medical school.