Sorry I was out last week, and I know this is beating a dead horse, but here are my responses to the above, FWIW:
As far as 60 Gy being the arm in cooperative group trials, let's keep in mind that the dose limit in bygone eras was based on toxicity limitations. You simply couldn't deliver more if you wanted to. In fact, where did 60 Gy originally come from: RTOG 7301 -- yes, as in 1973.
9410 prescribed to 63 Gy using marginally better technologies. I think it's disingenuous to say that "well, the volume must have received 60 since 63 Gy is the isocenter". That maybe true, but then again, it may not be. In any case, someone somewhere in 1994 decided that 60 Gy is probably inadequate as a prescription dose. As far as 66 Gy goes, it has been used in at least two modern trials with modern techniques including the Vokes trial as mentioned and the French trial (
http://www.ncbi.nlm.nih.gov/pubmed/16087956?dopt=Abstract). It is a reasonable standard, is consistent with first principles, and has simply not been compared to 60 Gy in randomized fashion.
Also, it is not mere speculation to state that 60 Gy is likely to be inadequate. In fact, there is randomized evidence demonstrating that 60 Gy accrues no survival benefit. This dose (both as XRT only and chemoXRT) was compared against chemotherapy alone by Johnson et al (
http://www.ncbi.nlm.nih.gov/pubmed/2161633?dopt=Abstract), and there was no survival benefit. So why would anyone treat a patient to 60 Gy with all the concomitant toxicity for no overall survival benefit? Would it be to prevent local symptoms? If so, then let's call a spade a spade: 60 Gy is aggressive palliation, and not a definitive dose per this randomized trial. That is also level I evidence.
With regard to 0617, why is everyone so unwilling to state (or explain) the obvious: There were more local failures in the high dose arm, ergo tumors were missed. This, to me, should be the very definition of a poorly radiation oncology trial. And the refrain that "it's really tough to run a cooperative trial" is a pretty unsatisfying defense in support of 0617.
The RTOG has run some very important trials and I respect and admire them for it. However, it also has run some poorly designed trials as one would expect from an organization (A) that is made of human beings and (B) that makes decisions in committee. Unremitting, unconditional support for this organization and an unwillingness to say that it errs from time to time is a worse kind of dogma than prescribing to 66 Gy, IMHO.
Finally, the idea that survival gets better until a certain dose (such as 66 Gy or whatever) and then gets worse afterward as toxicities become fatal seems completely reasonable to me. Isn't that the the whole point of the classic two sigmoid curves graph demonstrating the toxic-therapeutic ratio?