Abstract: Objective To evaluate the role of integrated positron-emission tomography and computed tomography (PET/CT) in gross tumor volume (GTV) delineation for three-dimensional conformal radiotherapy for bone metastasis. Methods Three patients with multiple bone metastases were enrolled in this study, whose primary tumors were pathologically identified as lung cancer, liver cancer and renal cell carcinoma. In each case, 6 sites of bone metastases were selected, labeled as BM1 to BM6 which located in the lumbar, thoracic vertebra, rib, ilium, scapula and thighbone respectively. The GTVs of the 6 bone metastases were delineated on the CT scans for treatment planning by 8 radiation oncologists, and the results were compared with the delineation obtained on the basis of integrated CT and PET/CT for analyzing the interobserver variability. Results For BM1-5 with obvious bone cortex lesions by the carcinoma, the GTV delineated on the basis of CT was greater than that derived from PET/CT (P<0.05), whereas for BM6 with intact bone cortex, the contrary result was observed (P<0.05). For any of these bone metastasis, the interobserver variability in GTV delineation with PET/CT was less than that with CT. Conclusion PET/CT is useful for improving the accuracy of GTV delineation for the protection of the normal tissues during radiotherapy.