The answer lies as to the cause of the fluid.
Normal fluid in the lungs can be obstructed when lymph nodes are infiltrated by cancer. If the lymph nodes shrink (due to either chemotherapy or radiation) then the obstruction is relieved and the amount of fluid reverts back to normal (it isn’t really dry).
However, if the cause of the fluid is due to tiny deposits on the lining around the thoracic cage or around the lung, which causes fluid to seep out, the radiation may still be able to control the fluid. The limitation would be if the area involved with these tiny deposits exceeds the area that can be safely irradiated, then the control of the fluid would be inadequate.
For lymphoma, the first scenario is more likely, so hopefully things will improve.
The likelihood of cure or long-term survival depends on the type of non-Hodgkin's lymphoma and the stage when treatment starts.
Stage 1 and 2 are often treated with radiation limited to the site of the lymphoma and adjacent areas People with aggressive or highly aggressive lymphomas at a very early stage need to be treated with combinations of chemotherapy, often with the addition of localized radiation therapy Stage 3 and 4 Treatment may include chemotherapy with a single drug or as a combination of several different drugs.
Radiation therapy is treatment with high energy rays (such as x-rays) to kill or shrink cancer cells. Radiation given from a source outside the body (external beam radiation) is the kind most often used to treat NHL. It might be used as the main treatment for early stage lymphomas, but more often it is used along with chemotherapy.
Side effects of radiation may include mild skin problems or fatigue. Radiation to the abdomen may cause upset stomach and diarrhea. Often these go away after a short while.
In case you need more information, do keep us posted.