Is it cancer of the lymph nodes or cancer from elsewhere that has settled in the lymph nodes? Radiation is only effective if targeted at the area with the cancer growth.
If your uncle's has been identified as cancer of the lymph nodes and in a specific set of nodes, then I would imagine radiation would be effective.
My wife has breast cancer which spread and they found it in some of her lymph nodes. They removed all of them from under her arm, but she's receiving chemotherapy to kill the cancer cells which might have spread to other parts of her body. Following that she's have radiation as well, but only directed at the area of the original (now removed) tumors.