Dosimetry of Ionizing Radiation: In Search of an Ideal Detector
Proper dose measurement skills are of the utmost importance for all applications of ionizing radiation in medicine. For years, since the discovery of ionizing radiation, the delivered dose to exposed people has been evaluated by means of subjective methods. In radiotherapy, the unit “erythema dose” was widely used. The erythema dose was connected to the reaction of the skin to radiation. (Strictly: The erythyma dose is the amount of radiation which, applied to the skin, makes it turn temporarily red [erythematous]. Webster’s New World™ Medical Dictionary, 3rd Edition) In the early days of the discovery of X-rays, the Roentgen radiation was commonly used. Luckily, the Roentgen radiation deposits the maximum energy to the surface, i.e. in the case of radiotherapy to the skin. Careful observation of the redness of the skin allowed therapists to finish treatment in the right time, before a serious injury of deeper anatomical structures would occur. However, this type of measurement of delivered dose was very imprecise. It depended on the individual reaction of each single person. In 1924 an objective method, namely the unit of radiation exposure, was introduced. This unit, the Roentgen, was internationally accepted in 1928 during the II International Congress of Radiology held in Stockholm. It was based on the measurement of the ionization of air exposed to ionizing radiation. At that time the method of the measurement of charge has been well developed. The method of dose measurement, based on charge measurement has been developing for years and today is considered as the most precise and the simplest method of dose measurement. Nevertheless, new detectors and new methods of dose measurement are still developing, and, what has to be emphasized, is that there is no ideal radiation detector for all applications of ionizing radiation. In this lecture the theory of dosimetry will be presented alongside the most often used detectors in medical practice.
KeywordsDose Measurement Linear Attenuation Coefficient Mass Attenuation Coefficient Electronic Equilibrium Film Blackness
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