Absolute dosimetry on a dynamically scanned sample for synchrotron radiotherapy using graphite calorimetry and ionization chambers

Lye, J, Harty, P, Butler, D, Crosbie, J, Livingstone, J, Poole, C, Ramanathan, G, Wright, T and Stevenson, A 2016, 'Absolute dosimetry on a dynamically scanned sample for synchrotron radiotherapy using graphite calorimetry and ionization chambers', Physics in Medicine and Biology, vol. 61, no. 11, pp. 4201-4222.


Document type: Journal Article
Collection: Journal Articles

Title Absolute dosimetry on a dynamically scanned sample for synchrotron radiotherapy using graphite calorimetry and ionization chambers
Author(s) Lye, J
Harty, P
Butler, D
Crosbie, J
Livingstone, J
Poole, C
Ramanathan, G
Wright, T
Stevenson, A
Year 2016
Journal name Physics in Medicine and Biology
Volume number 61
Issue number 11
Start page 4201
End page 4222
Total pages 22
Publisher Institute of Physics Publishing
Abstract The absolute dose delivered to a dynamically scanned sample in the Imaging and Medical Beamline (IMBL) on the Australian Synchrotron was measured with a graphite calorimeter anticipated to be established as a primary standard for synchrotron dosimetry. The calorimetry was compared to measurements using a free-air chamber (FAC), a PTW 31014 Pinpoint ionization chamber, and a PTW 34001 Roos ionization chamber. The IMBL beam height is limited to approximately 2mm. To produce clinically useful beams of a few centimetres the beam must be scanned in the vertical direction. In practice it is the patient/detector that is scanned and the scanning velocity defines the dose that is delivered. The calorimeter, FAC, and Roos chamber measure the dose area product which is then converted to central axis dose with the scanned beam area derived from Monte Carlo (MC) simulations and film measurements. The Pinpoint chamber measures the central axis dose directly and does not require beam area measurements. The calorimeter and FAC measure dose from first principles. The calorimetry requires conversion of the measured absorbed dose to graphite to absorbed dose to water using MC calculations with the EGSnrc code. Air kerma measurements from the free air chamber were converted to absorbed dose to water using the AAPM TG-61 protocol. The two ionization chambers are secondary standards requiring calibration with kilovoltage x-ray tubes. The Roos and Pinpoint chambers were calibrated against the Australian primary standard for air kerma at the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Agreement of order 2% or better was obtained between the calorimetry and ionization chambers. The FAC measured a dose 3-5% higher than the calorimetry, within the stated uncertainties.
Subject Medical Physics
Synchrotrons; Accelerators; Instruments and Techniques
Keyword(s) dosimetry
graphite calorimeter
microbeam radiotherapy
synchrotron medical beam line
DOI - identifier 10.1088/0031-9155/61/11/4201
Copyright notice © 2016 Institute of Physics and Engineering in Medicine
ISSN 0031-9155
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