It was an idea before Homecoming, and even before this 2015 paper https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4547388/ But that aspect of Homecoming scripts were probably inspired by the general discussion of possible treatments over the years.

PTSD applies to more than just veterans. They're one of the most prominent discussed class of sufferers of PTSD, but there are victims of crimes, of simply accidents, or of war or terrorism that can also suffer PTSD.