New Patient; Patient Portal; Call Us: Greenbelt Office301-486-7580. ... We invite you to begin your new patient registration as soon as you'd like by following these directions: ... MD 20746 Phone: 301-868-0150 Billing Inquiries: 301-552-1270 Fax: 301-868-0243. Riverdale Office. 6510 Kenilworth Ave, Ste 1400,.