Mammogram before radiation - Is it necessary?

After my lumpectomy, I didn't do chemo but went on to radiation. Rad. onc. strongly requested that I get a baseline mammogram (breast surgeon didn't think it necessary since I'd had multiple mammo shots taken the morning of the surgery to place the wires/confirm size, etc.).

My rad.onc. explained that it was a good idea to get this new baseline mammogram for my file, so I did. It wasn't to help pinpoint where they'd radiate, at least not in my case. They knew I'd have full breast and then boosts at the end along the scar line. The simulation machine takes images of where your heart and lungs are and determines how you will lay and the angles of the rad machine, which is quite different than a mammogram. After the simulation, you will begin rad.treatments which are quite quick -- the setting you up to make sure everything lines up takes longer than the zaps -- and most places are really good at getting you in and out promptly.