I'm sorry for your father's sufferings!
I guess is very hard to accept that lung cancer disease is difficult to treat and that stage 4 has very poor prognosis.
There are different chemotherapy regimes, that are only palliative therapy (controlling and relieving the symptoms, this can, also, cause cancer to shrink, and slow the spread of the disease).
Rarely, chemotherapy can cause metastatic lung cancer to disappear completely, but these patients are still at very high risk of cancer returning. Therefore, patients with advanced disease are never considered "cured" of their cancer no matter how well the chemotherapy works.
Clinical trials usually include different combination and new chemo drugs.
You can check the following link for
alternative cancer therapies.