Beam dosimetry

The pattern of dose distribution from each linear accelerator has to be measured prior to clinical use. Due to absorption properties at such high energies, these measurements can be made using a small ioniza-tion chamber dosimeter in a tank of water. The dosimeter tracks across the beam at preset depths and dose profiles are recorded for a range of beam sizes, with and without wedges. It is also essential to measure calibration factors (known as output factors) which define irradiation time required for a specified absorbed dose.

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