New equipment for a radiation therapy simulator: a device for simplifying irregular field shaping and integrating...

Shaping of irregular treatment fields was facilitated by our newly developed Niwa-Fujikawa irregular field-shaping unit, which was mounted onto a standard radiation therapy simulator. The introduction of a "fieldgraph" led to the functional integration of the simulator and therapy machine. A fieldgraph is a radiograph of an irregular treatment field taken on the Niwa-Fujikawa unit at the same distance as the focus-to-shadow-tray distance of the corresponding therapy machine. The fieldgraph can be taken at the same time as the portal localization film. Through the fieldgraph, which is positioned on the shadow tray of the therapy machine, the irregular treatment field is directly projected onto the skin of the patient. Consequently, marking the irregular field on the skin of the patient is unnecessary. The authors believe that both the new unit and the fieldgraph contribute to greater efficiency and accuracy in daily application of radiation therapy.