A study of PET scan use for follow-up care for U.S. patients with lung and esophageal cancer shows a wide variation among hospitals, but the degree of usage appears to have no impact on survival.
http://journals.lww.com/oncology-times/Fulltext/2016/04250/PET_Scan_Follow_Up_Use_Varies_Widely,_But_Survival.14.aspx
PET Scan Follow-Up Use Varies Widely, But Survival Doesn't