has two different type: NSCLC vs SCLC(Non small cell vs Small cell carcinoma
stage iv cancer means disease have spread from lung to distal site(liver/bone/brain/para aortic lymphnode/suprarenal gland, etc.)
If its bone metastasis
than radiotherapy helps beside chemotherapy
if brain metastasis: again radiotherapy gives you help.
if its liver metastasis : change to second line of chemotherapy after your present sixth cycle of chemo.
over all survival is poor in lung cancer 4th stage.median survival is 8month.