Pea sized lump post radiotherapy

I have been diagnosed with Squamous Cell Carcinoma of the Sinuses and just finished 7 weeks of radiotherapy 4 weeks ago  (chemo before that). Last week, I detected a hard pea sized lump beneath the skin on my neck, just beneath my Adams apple. My oncologist is going to look at it during a check up next week, I’m sick to death with worry. I have a CT scan in December to see how successful treatment has been, have to wait with this anxiety about it having spread already.

Anybody had similar at all?