Prevention, Large scar after surgery and radiotherpy

Hello. Seven years ago I had thyroid surgery. About two years later, I developed a red spot on the scar that kept growing. After a biopsy, it turned out to be skin cancer scc. I had already thought a lot about it and realized that it was probably my fault for not protecting the scar from the sun. Then I had surgery and radiation therapy. I was recommended Regencorr cream to reduce the scar and do prevention against recurrence.
I would like to ask the people on this forum who know about this:
Should the cream be applied to the entire scar and neck, or only to the area where the tumor was removed and keloid scars remain? Would applying the cream under a film be helpful in my case or is it not necessary?