Design and fabrication of a half-beam wedge for treatment of breast patients

The Radiation Oncology Department of Kansas University Cancer Center on the average treats approximately 60 breast patients per year. Many of them require large field sizes with widths greater than 20 cm. Our purpose is to design a half-beam wedge that is lighter in weight than a standard wedge for larger field sizes. This could replace the compensator and reduce the number of monitor units. We have designed and fabricated half-beam wedges for a Varian linear accelerator, with the angles of 15, 30 and 45 degrees for a 6 MV photon beam. A set of dosimetry data for these wedges was entered into a treatment planning computer. The treatment plans generated using these newly designed wedges were compared with those using standard wedges.

From basic principles, the geometry for the design of the wedges was calculated for three angles, 15, 30 and 45. Using trays provided by Varian, three brass wedges were milled and attached to the trays. Measurements were taken in a water phantom with three wedge angles, 15, 30 and 45, for treatment planning purposes.

The design and fabrication of a half-beam wedge for the use of treatment with large field sizes could reduce the need for fabrication of a compensator. This would also reduce the time required for treatment and give a better dose distribution.