Top-10 schools can get people with thousands of hours of volunteering. 150 hours for a single year is on the low side for schools like that; you might be able to get away with it if the rest of your app is rock-solid: strong research (preferably publications), 3.8+ GPA, and 520+ MCAT. How much do you want a top-10 school? Another year of clinical volunteering would do you wonders.