Is it ever that a bone scan pick up on dead cancer cells after one has been treated for bone cancer?

Yes: Bone scan is usually repeated to evaluate the progress of treatment.

Yes and no.: The degree of tracer uptake depends on several factors such as the size and the type of tumor. Bone scan detects the bone metabolism surrounding the tumor. Usually the uptake will be proportionnal to the degree of "invasion" of the bones but sometimes a lesion which is healing can also be seen as a "hot" spot for many months because of the healing process. Serial scans are needed for evaluation.

Bone sc not accurate: Bone scan can be active with primary bone tumor and can be active in repair phase. If multiple phases of bone scan are performed, early soft tissue phase and delayed skeletal phase, the soft tissue phase is more accurate in predicting cancer cell kill. The most accurate study now available is the pet/ct scan for detecting viability of tumor by assessing its glucose metabolism with f18 fdg.

Yes, it can: A bone scan picks up activity in bone. The activity can be from normal cells repairing bone, or it can be from cancer cells. New areas of activity are more likely to be from cancer. Activity in spots where there was cancer in the past could either be cancer or repair. Cancer is associated with a high amount of activity, while repair is usually lower.