The pain probably relates to the depth of your breathing, when
smokingQuitting smoking
Smoking - tips on how to quit
Smoking and copd (chronic obstructive pulmonary disorder)
Smoking and smokeless tobacco
Smoking hazards. This causes stretching of the chest wall, including scar tissue and this is probably responsible for your pain.
Radiation can damage lung tissue. It can result in pulmonary fibrosis or scarring, but almost never, pain. Please check with your oncologist to see if this is due to cancer.