A technique for evaluating cast foam positioning and immobilization devices used in breast cancer radiotherapy

Patient setup reproducibility when Alpha Cradles* are used is not well documented. A simple technique is described that localizes longitudinal and transverse planes in breast setups utilizing 4 mm lead-sphere markers embedded in a modified HS-2 Alpha Cradle. The markers are positioned in the cradle coincident with the projected simulator central axis crosshair when the x-ray beam is directed vertically down through a setup point on the patient. A reference film recording patient position relative to the Alpha Cradle is taken through the setup point at the end of the simulation procedure. On the treatment machine, the images of the lead markers on the portal film, taken through the same setup point, indicate longitudinal and transverse planes. These planes are then used to correlate and quantitate the reproducibility of the original reference planes. This technique is easily initiated, and when used in conjunction with a careful analysis of conventional treatment portal films, is very useful in determining the accuracy of patient repositioning in the Alpha Cradle, and precise field placement. Results of a study utilizing a modified HS-2 Alpha Cradle will be presented.