Welcome here and so very sorry to learn of your husband's diagnosis. Wow, 18 months of back pain, that is a lot to put up with.
Oncologists come in two flavors: the medical oncologist and the radiation oncologist. Of these the medial oncologist is the generalist; they see and treat all kinds of cancer primarily with chemotherapy. The radiation oncologist specializes in radiation therapy using ionized radiation or accelerated protons. Both my medical oncologist and radiation oncologist practiced in the same clinic but there is no need for proximity to have successful treatment. Radiation oncologists tend to be colocated with hospitals because the radiation or proton generating equipment is expensive and often found in hospitals.
My medical oncologist was captain of my lung cancer team. After 15 years of surviving lung cancer, he still is and I see him twice a year. I'll likely have oncology consultations for the rest of my life because lung cancer often recurs after treatment so follow-up is prudent.
It sounds like your husband's doctor is using radiation as a palliative means to reduce his back pain. Ten cycles suggest he is receiving precision radiation; that is IMRT, IGRT or SBRT. I had SBRT as my last treatment and it worked. This is a good plan and there is no problem with the order of treatment. I'd rather have my pain eliminated before chemo. Here are some tips and tricks that may assist with his chemotherapy.
You mentioned a biopsy. Did you receive a diagnosis, that is a type of lung cancer? It may be small cell or non small cell which is further classified as adenocarcinoma, Squamous cell or large cell. Knowing the diagnosis will allow us to help you with chemo side effects and provide the basis of our experience in treatment.
Stay the course.