20 C.F.R. § 10.806
For professional medical services, the Director shall maintain a schedule of maximum allowable fees for procedures performed in a given locality. The schedule shall consist of: An assignment of Relative Value Units (RVU) to procedures identified by Healthcare Common Procedure Coding System/Current Procedural Terminology (HCPCS/CPT) code which represents the relative skill, effort, risk and time required to perform the procedure, as compared to other procedures of the same general class; an assignment of Geographic Practice Cost Index (GPCI) values which represent the relative work, practice expenses and malpractice expenses relative to other localities throughout the country; and a monetary value assignment (conversion factor) for one unit of value for each coded service.
20 C.F.R. § 10.806