Physical characteristics of X-rays scattered by phantom in the transmission dose for radiotherapy

In radiotherapy, the transmission dose includes the dose contribution by scattered photons from the body volume of a patient exposed to the X-rays, and this affects clinic applications of the transmission dose method of radiotherapy. In this study, distributions of transmission dose under different conditions of 6 MV X-ray irradiation were measured on the central axis and the off-axis positions.The transmission dose composed of the primary dose and the scattered dose was analyzed.The primary dose was extracted from the transmission dose and the corresponding scattered dose was computed to study physical characteristics of these dose scattered by phantom. (authors)