Denise, I can only share with you my wife's experience in the areas you asked about. (1) I would think more than the sternum should be scanned. Lucie has had bone mets in a number of areas, and some were found because they did a whole body scan of the bones. Her onc uses CT, MRI and x-ray where appropriate. He will have scans done in any area where she has had severe pain. But since she has bone mets, he does a full bone scan every now and then, even if there is no pain.
(2) Lucie's medical onc has her go to the radiation inc. whenever a tumor is discovered and it is causing severe pain or is threatening the integrity of the bone. Radiation and chemo can be done together, but he did not have every met radiated.
(3) My wife's onc uses primarily CT. MRI and x-ray for scanning. She has had only one PET scan in the past year and probably will have another in a few months. Her onc uses PET just to be sure there are no new surprises.
I hope this helps add to your info. Don