It is not entirely clear how to followup definitively treated osteosaroma. ESMO recommends clinical followup every 6 weeks to 3 months in years 1 and 2 after diagnosis, every 2–4 months in years 3 and 4, every 6 months in years 5–10 and every 6–12 months thereafter. Each visit should include a history and physical examination and a chest X-ray [IV, C]. X-rays of the primary tumor site are recommended every 4 months until the end of year 4 [IV, C]. Late metastases may occur >10 years after diagnosis and there is no universally accepted stopping point for tumor surveillance. NCCN in its osteosarcoma guideline, p. 8 recommends “chest imaging” without specification. It does recommend PET for initial staging and thereafter (also bone scan, p. 11). It says that CT scan should be done if chest Xray becomes abnormal9p.29).
S. Bielack et al, Osteosarcoma: ESMO Clinical Recommendations for diagnosis, treatment and follow-up Ann Oncol (2009) 20 (suppl 4): iv137-iv13
nccn.org, Bone Cancer, Osteosarcoma