Abstract
In stereotactic irradiation using linear accelerator, lateral electron equilibrium must be considered for small field. The dosimetry has some problems, for example, the accuracy of measurement depends on detector volume. The dosimetry of small field has been performed in the axis direction (chamber stem parallel to the beam axis) of reference ionization chamber. However, this method has some problems which are a stem effect, an effective measuring center and so on. Measurements were performed using 6 MV x-ray beam (Mitsubishi ML-6M LINAC) to a water phantom. A small volume parallel-plate ionization chamber was used in this study. The effective point of measurement was on the inner face of the front surface, the chamber was pointing axis direction. In this position, the effect of the irradiated cable has been considered because the part of a cable was inside the field. We studied the stem effect of ionization chamber. As a result, dose evaluation was not influenced by the stem effect due to the length of a cable.
