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ESTRO 2020

Session Item

Physics track: Dose measurement and dose calculation
9319
Poster
Physics
00:00 - 00:00
Ion chamber beam quality correction factors for brachytherapy dosimetry measurements
ZOI THRAPSANIOTI, Greece
PO-1413

Abstract

Ion chamber beam quality correction factors for brachytherapy dosimetry measurements
Authors: Costantinos Hourdakis.(Greek Atomic Energy Commission, Licensing and Inspections, Athens, Greece), Pantelis Karaiskos.(National and Kapodistrian University of Athens, Medical School Laboratory, Athens, Greece), Evangelos Pantelis.(National and Kapodistrian University of Athens, Medical Physics Laboratory, Athens, Greece), Zoi Thrapsanioti.(National and Kapodistrian University of Athens, Medical School Laboratory, Athens, Greece)
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Purpose or Objective

The need for a quality control protocol in brachytherapy is well recognized. The purpose of this work is to calculate the beam quality correction factors of a series of detectors for experimental dosimetry measurements around brachytherapy sources.

Material and Methods

Beam quality correction factors (KQ,Qo) for the PTW PinPoint -31014, -31016 and the Exradin A16 thimble chambers were calculated as a function of radial distance from an 192Ir HDR source centered in 20cm radius spherical water phantom. All calculations were performed using the egs_chamber user code of the EGSnrc Monte Carlo code. All detectors were assumed to be calibrated in a reference 60Co 10x10cm2 beam. The contribution of volume averaging and the perturbation of the wall, stem and central electrode to the correction factor was studied.

Results

Beam quality correction factors of 1.03, 1.01 and 1.02 were calculated for the PinPoint 31014, 31016 and Exradin A16 ion chambers respectively at 1cm distance from the source. These values were found to decrease with increasing distance from the source due to the decrease of the contribution of the volume averaging effect to chambers’ signal. The central electrode and wall material of the chambers was found to perturb the signal in the 192Ir beam energies by 3% and 1%, respectively at 1cm away from the source. These perturbation values were found to increase with increasing distance from the source due to the increased contribution of low energy scattered photons.

Conclusion

Beam quality correction factors KQ,Qo for three ion chambers were calculated for dosimetry measurements around 192Ir brachytherapy sources. Besides volume averaging effect, the signal of the chamber was found to depend on the wall, central electrode, material and distance from the source.