I'm sorry to hear this, Delly. It's unusual that cancer will grow during radiation, it usually shrinks, although there can be some inflammation of lymphatics, and as said, is not a good indication. I had tumors pop up twice in the neck while waiting for different cancer surgeries, which were removed with the other cancer thankfully, but not during treatment, which could have possibly happened if they weren't found in time.
If may or may not be a lymph node, as some were said to have been dissected, not sure of type though, and what levels, and I have found as far as myself, not all are always removed, and had several found with each dissection (5) I had, and being there are so many in the neck, around 300, mostly microscopic, but everyone is different in that amount, and location. As far as it not being a lymph node has happened to me. After a neck dissections, radiation, even surgery, cancer finds an alternate route if the lymphatic flow is disrupted, so cancer can travel anywhere, usually the weakest link.
On the other hand, the tumor can be radio resistant from a number of things, the neck receives a lower radiation dosage usually than the primary, can be out of the radiation field, etc.
I'm not sure what the doctors may do. It sounds like the current radiation therapy is not finished yet? Maybe they will do another simulation, treatment plan, and give higher dosage to this new cancer, and finish the current radiation treatment, then do a neck dissection, possibly add chemo as a radio sensitizer. They can possibly stop radiation, do a dissection, but that has risk of tumor regeneration, and incomplete or delay in further radiation treatment.
Cheryl mentioned IORT and Proton Therapy, which may be a possibility, not sure though, plus the fact it may not be available in England. Brachytherapy is, I believe, and is used as a boost dose with IMRT radiation for HNC, so that may be an option maybe, and Cyberknife too.
http://www.royalmarsden.nhs.uk/diagnosis-treatment/cancer/pages/head-neck.aspxI tried thinking of any possibilities, and hope the doctors come up with a good course of action, and know better than I do.
Good luck with everything, ask any questions, and keep us posted.
