The ulcers could be anything, mucostis, thrush, herpes simplex, irritation from teeth, and as mentioned, have it checked out by an ENT. The tonsils are part up the lymph system, and are highly lymphatic, not to mention any scar tissue, inflammation from treatment, so they usually show uptake like some other organs do. My ENT took a biopsy of my tongue ulcer once, even though it was most likely from a cracked tooth rubbing against it, which it was, and continues to be a problem. Just to answer the BOT question, it's part of the Oropharyngeal or Oropharynx, along with tonsils, valeculla, soft palate, pharyngeal wall, uvula, and treatments are usually the same as with the tonsil, and radiation usually treats this entire area anyway, but already having radiation makes treatments more limited in the future, but not impossible. Most leukopatria (white, less invasive) and Erythroplakia (red) ulcers occur in the mouth, and if in the oropharynx it's on the soft palate. Good luck with everything.