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Determination of percentage depth‐dose curves for electron beams using different types of detectors
Author(s) -
Ding G. X.,
Yu C. W.
Publication year - 2001
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1350436
Subject(s) - stopping power , fluence , dosimetry , ionization chamber , electron , ionization , atomic physics , percentage depth dose curve , physics , detector , nuclear physics , optics , computational physics , materials science , nuclear medicine , irradiation , ion , medicine , quantum mechanics
According to the new AAPM TG‐51 dosimetry protocol, reference dosimetry for electron beams is performed at depth of d ref= 0.6 R 50 − 0.1 ( cm ) instead of d maxrecommended in TG‐21. In clinical practice most electron beams are normalized at d max . Therefore it becomes more important to get an accurate percentage‐depth‐dose (%dd) curve particularly for higher‐energy electron beams in which the depth d refis away from d max . When ionization chambers are used in determining %dd curves the water‐to‐air stopping‐power ratios and the fluence correction factors are required. The TG‐51 recommends that the stopping‐power ratios for realistic electron beams be used instead of the monoenergetic stopping‐power ratios used in TG‐21. This investigation aims to study the effects of those correction factors on the determination of %dd curves. We observed 1% deviations in the value of %dd at d reffor 15 and 18 MeV beams between a plane‐parallel NACP and a cylindrical IC‐10 chamber without considering the fluence correction factors P fl . We explored a method to derive the fluence correction factors at any depth by using the existing fluence correction data at d maxand tested its feasibility. We compared %dd curves measured by a diode detector and a NACP chamber with stopping‐power ratios recommended by TG‐51 and those recommended by TG‐21. We found that for 15 and 18 MeV beams the difference in the values of %dd at d refbetween using those two different stopping‐power ratios is about 0.5%. Excellent agreement is found between %dd curves measured by the diode and by the NACP chamber when the stopping‐power ratios recommended by TG‐51 are used.