I am so sorry that you and your dog are going through this difficult situation. I know this must be a very difficult time for you.
Here are some statistics that may help you decide how to proceed.
Survival time of dogs with nasal tumors that do not undergo any type of treatment is approximately 3 - 5 months.
Surgery alone did not increase survival time in dogs with nasal tumors, so this is not recommended, although with focal tumors, surgery can be done and then followed up with radiation therapy.
Radiation is the treatment of choice for nasal adenocarcinomas. In recent studies, the survival time of dogs treated with radiation therapy ranged from 7 months to 47 months, with the average being 14 months. The 1 year survival rate ranged from 43 to 60%, and the 2 year survival rate ranged from 11 to 44%.
So, to answer your question, radiation definitely is your best option to treat this disease and there is a good chance that it will significantly extend your dog's life, but it is not likely to result in a cure for this condition. I know this is hard to hear, but it is important that you have realistic expectations if you decide to go forward with this option.
I hope this information is helpful. If so, please click Accept. If you have additional questions on this topic, please let me know.