It's a tough subject to find and has never been properly defined. Here are some links"

http://www.ro-journal.com/content/1/1/40
http://linkinghub.elsevier.com/retrieve/pii/S0196070900202433

"Acceleration of Radiation Dose: Another strategy in the treatment of head and neck cancers is to administer radiation therapy at more frequent and intensive doses. Patients with cancer of the head and neck may benefit from higher doses of radiation therapy that are administered twice daily compared to standard therapy consisting of lower doses administered once a day. However the current standard therapy is to administer radiation only once a day.

One of the largest clinical trials of the past 2 decades involving the treatment of head and neck cancer showed that the risk of a local cancer recurrence may be reduced in patients with locally advanced head and neck cancer by using increased frequency and doses of radiation therapy. In this study, over 1,000 patients with locally advanced head and neck cancer received radiation therapy either once daily or twice daily. Higher doses of radiation were delivered to the group of patients receiving treatment twice daily, whereas standard doses of radiation were delivered to the group of patients receiving treatment once daily. Two years following treatment, 56% of patients receiving radiation treatment twice daily were free of cancer recurrence, compared with 46% of patients who received radiation once daily.

(please note some in many cases the radiation dose frequency is simply done by adding a few more days and /or increasing the daily fractionalized dose rate higher then 1.8 Gy - my comments)

Research indicates that accelerated boost radiation therapy can also be effective in elderly patients with cancer of the head and neck who are healthy enough to tolerate this more aggressive treatment. In one study, accelerated boost radiation therapy was administered to 45 patients, age 70 or older, with cancer of the mouth, throat, or larynx. The results were compared to a similar group of patients who were younger than 70 years of age. Among the older patients, 68% lived 3 years or longer after treatment, compared to 62% for the younger patients. The local cancer was controlled in 73% of the older patients and 68% of the younger patients."

Full link:
http://patient.cancerconsultants.com/CancerTreatment_Head_and_Neck_Cancer.aspx?LinkId=53927

Another link:
http://www.medscape.com/viewarticle/518831

The last link has some interesting onformation on Amofostine as well.

Please note that some of these links are a few years old.

There is no substitute for going to a Comprehensive Cancer Center.

This whole subject will make your head spin!