Sorry to hear about your Father. Depending upon his performance status or in other word, inspite of the cancer how fit he is. Based on this if he is fit enough, he could have palliative chemotherapy
and radiotherapy. If he is bed ridden and depends everything on others for his daily living activities, then it is better to let him have peace with sedatives and strong pain killers. Ultimately, it depends on your father's wish how aggressive he want to be treated. The prognosis is normally very poor with stage 4 disease lung cancer
, less than 3 months but sometimes people defy the normal trend, nature takes it own course.