Seroma & radiotherapy

I had a lymph node clearance in August as well as a lumptectomy. 7 weeks ago I had radiotherapy. 2 weeks after that, under my arm became painful. Saw the Dr last week. He’s querying if I have got a seroma. Rhe area is swillen & there’s a lump. The last CT scan before the rads picked one up in that area. Can rads make the seroma grow in size or become more painful. If not what is causing it. Been given the all clear but am taking Capecitabine to stop the cancer from coming back. Im on the 2nd cycle of 8. Worried this lump & swelling is something more sinister. 

Hi , you could also ask about this in Ask the Nurses section they may be able to give some advice ? I had a really big seroma under my arm too but luckily it had resolved before radiotherapy they are very uncomfortable , I hope you get to the bottom of what’s causing it soon x