Hi bond, sorry to hear about your father and his lung cancer - My mum has just had to undergo treatment herself for lung cancer, so I can empathise.
Obviously I dont know the specifics of your fathers tumour, so I cant comment directly. Broadly speaking, there are 3 treatment modalities.
1. Surgery
2. Chemotherapy
3. Radiotherapy.
These treatment modalities can be used in isolation or combination, depending on the clinical evidence supporting the particular treatment regimen. The type of treatment offered is very dependent upon the type of cancer ( small cell or non small cell, for instance), the stage the tumour is at ( stage 1 being small and localised, stage 4 being large/diffused and metasized to other organs), the location of the tumour, and the underlying health of the patient.
Chemotherapy comes in 2 types - cytotoxic and hormone. In this case, the chemo will probably be cytotoxic, and the aim of the therapy is to slow/halt the spread of the cancer, and to reduce/remove some of the tumour mass. The unfortunate side effect of chemotherapy it doesnt just target cancer cells, but healthy cells as well, hence the severe side effects. Often you will see a treatment plan that uses chemo to systemically and non specifically attack the tumour. Radiotherapy is then used, since radiation kills cells also. Radiotherapy is a targeted therapy.
Offering the 2 therapies together often gives the best chance of treating the cancer.
All the best to you and your dad. You may find the following link useful ;
http://www.cancerhelp.org.uk/help/default.asp?page=91