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Dosimetry of pulsed clinical proton beams by a small ionization chamber
Author(s) -
Nohtomi A.,
Sakae T.,
Tsunashima Y.,
Kohno R.
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 - 10.1118/1.1380435
Subject(s) - ionization chamber , dosimetry , proton , beam (structure) , calibration , ionization , absorbed dose , physics , nuclear physics , nuclear medicine , atomic physics , materials science , optics , ion , medicine , quantum mechanics
Response of a micro volume (0.01 ml) ionization chamber has been studied with pulsed proton beams which are used for clinical purposes and has been compared with those of some JARP ionization chambers (0.6 ml). All chambers used had been calibrated by standard60 Co beams at the Electrotechnical Laboratory (ETL) and exposure calibration factors, N X , were obtained on advance. Two methods are used to compensate the general recombination which occurs during pulsed beam irradiations: theoretical correction by a Boag's formulation and a modified two‐voltage technique. An evaluation of absolute absorbed dose‐to‐water is performed on the basis of the protocol provided by ICRU report 59. The results imply that, to a first approximation, both chambers indicate the almost same result within 2% when unknown chamber‐dependent parameters of the micro chamber are tentatively assumed to be identical to those of the JARP chamber for the calibration with60 Co beams. The about 1.5% discrepancy observed in the response of both chambers is not discussible due to presumably 1–2% uncertainty of the protocol of ICRU report 59 which does not include any chamber‐dependent corrections for the perturbation effects in proton beams.