Why don't you call up the oncology office and ask a nurse these questions? If they sent you there for the mammo then they probably has answers those same questions before.
In the future, when someone does a test differently then you have experienced in the past, ask them directly why they are doing the test different then you have had it done before. By HIPPA law you are entitled to have all of the information you ask for. You can get answers to questions, copies of you tests (printed reports and actual films if you want) and any other part of you chart from whoever you have a visit with.
That's the best I can offer. Let us know what they say, Thanks
take GOoD care