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External beam


For the acceptance testing, commissioning and QA of external beam equipment a large number of dosimetric measurements is required. A dosimetry protocol provides the formalism and the data to relate a calibration of an ionization chamber at a Standards Laboratory to the measurement of absorbed dose to water under reference conditions in the clinical beam. Relative dose measurements, using various types of dosimeters, provide treatment beam characteristics needed for clinical use, including data required to operate a treatment planning system for this particular type of equipment. For special techniques in radiotherapy specific phantoms having multiple dosimeters are often used.

Important Principles

In addition to the local secondary standard and field ionization chambers, additional equipment is needed for absolute and relative dose measurements including an electrometer, thermometer, barometer, linear rulers, phantoms, beam scanning systems. Other dosimetry systems are used for specific purposes such as systems for relative dosimetry (e.g., TLD, diodes, diamonds, film), for in vivo dosimetry (e.g., TLD, diodes) and for radiation protection measurements.

Introduction to References

A general discussion of the various types of dosimeters is presented in Chapter 3 of the IAEA Radiation Oncology Physics Handbook. Calibration of high-energy external beams is discussed in Chapter 9 of the Handbook while details of absolute and relative dose measurements can be found in Report TRS 398 and in the Handbook.