Holy Cross Hospital's announcement that it hopes to build a hospital in Germantown, MD, is just the latest example of a baby boomer-fueled building frenzy sweeping the healthcare industry in Maryland's Montgomery County. Over the past several years, all five of Montgomery's major medical centers have decided to expand, upgrade their facilities or build new ones. What's happening in the county mirrors a national trend, fueled by concerns that aging baby boomers will put new demands on the healthcare system and that old hospital buildings can no longer accommodate changing and complex medical technologies, experts say.