Lymph Involvement

My husband has just gone through 6 aggressive rounds of chemo to deal with a large thoracic mass. It has disappeared but the oncologist is concerned with several lymph nodes is the area. We are going back to the surgeon because he also has a papillary thyroid cancer which they have ignored due to the severity of the sarcoma. The oncologist mentioned that the surgeon may want to remove the lymph nodes as well. Wouldn't a PET scan help diagnose these more throughly before surgery is undertaken?