Hi Uk33,
It is good to hear from you, but I am sorry your uncle is feeling so much fatigue.
I had radiation therapy and chemo after surgery, and the radiation really affected my energy levels with effects that went on for weeks after. The fatigue slowly got better with time.
Here is some information on cancer-related fatigue from the National Cancer Institute. It includes discussion of radiation-caused fatigue, and has tips for dealing with fatigue if you scroll down toward the end.
PDQ® Supportive and Palliative Care Editorial Board. PDQ Fatigue. Bethesda, MD: National Cancer Institute. Available at: https://www.cancer.gov/about-cancer/treatment/side-effects/fatigue/fatigue-pdq Accessed 03/16/2021. [PMID: 26389259]
I hope your uncle feels better soon and that the radiation helps with his pain. Regards, Mary