Our 28 year old daughter 3 years ago was diagnosed with HL, stage 4. She went through the usual 6 months of therapy, and though radiation was discussed, her doctor was of the opinion that unless it is specifically indicated that it probably should not be done. She did not have radiation, and today remains free of reoccurance.
I have done much study on this subject, and am of the opinion (supported by a great deal of research) that the value of radiation following chemo is very small, especially when compared to the increased risk of other cancers and problems caused by radiation.
Take charge, do your own research, present it to your medical team, and make an informed decision with them.
Blessings . . .
Dave