You might want to check the CyberKnife brain tumor discussion board:
http://www.cyberknifesupport.org/forum/default.aspx?f=1
The doctors who monitor the questions on that site are very helpful...tell them the size of your mets, how much they've shrunk, and ask them what they think. If your mets are receeding after WBR, your docs probably don't want to give you add'l radiation unless the mets stop shrinking and start growing (maybe WBR will be all that is needed). What will be very important is to watch the mets closely with MRIs, and if there is a reversal, look into CyberKnife, which is the most precise, least invasive form of stereotactic radiation therapy. You do need to catch the mets when they are relatively small for CyberKnife treatment.