Radiotherapy and the soft tissues


I'm really not sure where to place this but if I could ask somewhat of a logistical question, in a case where activity is found in the soft tissues, without corresponding anatomic abnormalities on a CT scan, how can radiotherapists adequately plan treatment and target such an area?

Would this be based on the results of a PET scan as, assumedly, a CT scan alone would be of little benefit in the planning stages? Or is radiotherapy to soft tissues impossible?

My father is considering radiotherapy for the soft-tissues lateral to his right hip following treatment for triple hit non-hodgkins lymphoma, as his PET-CT scan post 6 cycles of EPOCH was clear in all areas bar a tiny focus of uptake in these soft tissues.

We are also concerned about the possibility of secondary malignancies following radiotherapy to an area such as this,

Any feedback shared is gratefully appreciated,

Kindest regards,