Glad to. Adjuvant treatment is done in conjunction with another primary treatment(s) in search for a cure. Slavage therapy is done to improve the quality of life when a cure is improbable.
For example, All of my treatments after surgery have been done because I chose to add them in hopes I would beat the statistics and not ever have the disease relapse. They have been done as adjuvant treatments.
In the case of an individual with advanced prostate cancer in a great deal of pain, say in the hips or legs, they can elect to have radiation performed where an accumulation is identifiable in hopes that the pain will reside or that the treatment will add time to ones life. That is salvage treatment. At any time during an incurable disease can be made less painful or more manageable, the treatment would be considered salvage treatment.
In Pelahatchie's case, he is surely hoping by adding radiation he can stop any progression from leaving the local area and return to remission, which by the way he may still be in. I would also suggest that he consider talking to his medical oncologist about a brief stint on hormone deprivation to shrink the target before hitting it with RT. This logic is common when considering adjuvant RT.
From the Journals:
Salvage therapy: A final treatment for people who are nonresponsive to or cannot tolerate other available therapies for a particular condition and whose prognosis is often poor.
Adjuvant therapy: Treatment that is given in addition to the primary (initial) treatment.
Adjuvant treatment is an addition designed to help reach the ultimate goal. Adjuvant therapy for cancer usually refers to surgery followed by chemo- or radiotherapy to help decrease the risk of the cancer recurring (coming back).
In Latin "adjuvans" means to help and, particularly, to help reach a goal.