Is it appropriate to treat patients with limited metastases with whole brain radiotherapy and a concurrent simultaneous integrated boost?  

In reading through the policy of one of my state's private insurance companies, I came across something with which I'm not familiar, namely treating patients with limited brain metastases with whole-brain IMRT incorporating a simultaneous integrated boost to focal lesions.  I've not been successful in identifying any literature to support this.  Can anyone point me in the right direction?  Does anyone know of any standard parameters used in this situation?  (e.g. What margin would you place on individual lesions?  What limits would you place on normal brain tissue beyond the metastases?)  In the era of ultra precise IGRT, it seems like an exceptionally wise idea, but as always, I want to follow a data-based approach!