I respectfully disagree with Gary on RIF while acknowledging that in 20th century medical schools it was taught that radiation fibrosis is a permanent irreversible condition, despite the fact that its underlying mechanism remained uncertain. In 2005 there was a cleverly titled JCO article The Irreversibility of Radiation-Induced Fibrosis: Fact or Folklore? about using Vitamin E & pentoxifylline. NIH is running a clinical trial on this combo.

But my personal experience is different than the textbooks
Not only were my neck muscles totally fried once, they were fried twice. My neck literally felt like petrified wood. Not an exaggeration - you could thump your fingers on my neck, esp the left side and it sounded just like hitting hardwood. Very very slowly I am regaining muscle tone and function due to daily Yoga and stretching. Half of my neck has regained soft non fibrous texture while the left half which got the bulk of the radiation just feels "tight" and "hard" but not like petrified wood anymore. My ENT is amazed at the progress and attributes it to increased blood flow and stubbornness
It has been 2 and half years after the second round of radiation and therapy and I am still have major noticeable stiffness yet my ENT expected it to get worse not better so IMO there is hope especially with the NIH trials.
Keep the Faith
Charm