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Partial volume characteristics of ionization chambers in kilovoltage x-ray exposure measurements

Published online by Cambridge University Press:  24 August 2011

Syed F. Akber  and
Than S. Kehwar
Syed F. Akber
Affiliation:
Consulting Physicist, Lorain, OH 44053, USA
Than S. Kehwar*
Affiliation:
Consulting Physicist, Lorain, OH 44053, USA
*
Correspondence to: Than S. Kehwar, Ph.D., D.Sc., University of Pittsburgh Cancer Institute, UPMC Cancer Centers, Pittsburgh, PA 15232, USA. E-mail: drkehwar@gmail.com
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Abstract

The partial volume (spatial) response of four ionization chambers (Keithley) in kilovoltage X-ray beams, generated by the Philips Super 80CP X-ray unit, was assessed. The volume of the ionization chambers were of 10 cm3, 15 cm3, 150 cm3, and 600 cm3 used with Keithley electrometer Model 35040. The beam output was measured using a monitor chamber (Radcal 6.0 cm3) placed close to the collimator. The source to chamber distance was kept constant at 1 m. For the measurement of the response of ionization chambers of 15 cm3, 150 cm3, and 600 cm3, a slit of 2.0 mm width was made in a lead sheet of 3.2 mm thick and size of 30 × 30 cm2 and was placed on the ionization chamber. The measurements were made for 81 kVp, 400 mA, and 0.25 s and the slit was moved at an increment of 2.0 mm over the entire length of the chamber. For the measurements of the ionization chamber of 10 cm3 (CT chamber), the beams of 120 kVp, 200 mA and 0.2 s were generated, and a slit of 5 mm width was made in a similar lead sheet that was moved at an increment of 5.0 mm. From the result it appears that the sensitive volumes of the ionization chambers affect the response of the ionization chamber to incident radiation.

Keywords

Ionization chambermonitor chamberpartial volume responsesensitive volume
Type
Original Article
Information
Journal of Radiotherapy in Practice , Volume 11 , Issue 3 , September 2012 , pp. 184 - 188
Copyright
Copyright © Cambridge University Press 2011

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