Numerically produced compensators for conventional and intensity modulated beam therapy

Abstract

A study is performed to assess the utility of a computer numerically controlled (CNC) mill to produce missing tissue compensating filters and for the delivery of intensity-modulated beams for inverse treatment planning. A computer aided machining (CAM) software is used to assist in the design and construction of such filters. Geometric measurements of stepped and wedged surfaces are made to examine the accuracy of surface milling. Results show that the deviation of the filter surfaces from design does not exceed 1.5%. Effective attenuation coefficients are measured for CadFree and Cerrobend in a 6 MV photon beam. The ability of the CNC mill to accurately produce surfaces is further verified with dose profile measurements in a 6 MV photon beam. Dose profiles, measured beneath the test phantoms and beneath a flat phantom are compared to those produced by a commercial treatment planning system. Agreement between measured and predicted profiles is within 2%, indicating the viability of the system for filter production