Centre News and Events
Inter-Centre Study
6th Mar 2009
From September to October 2007, Perth Radiation Oncology participated in an inter-centre test of agreement between field dosimeters used for calibration of linear accelerator treatment beams.
Reference dosimetry is transferred between a national standard at the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) and Perth Radiation Oncology (PRO) via a secondary standard dosimeter.
Subsequently, all clinical linear accelerator beams at PRO are routinely calibrated with field dosimeters that have been inter-compared against the secondary standard.
The 2007 inter-centre study is an independent confirmation of correct application of the field dosimeters for treatment dose calibration.
The field dosimeters in use at for PRO are in good agreement with similar instruments from an independent dosimetry chain and also with ARPANSA-owned field dosimeters.
The observed differences in this study were significantly smaller than theoretical variations of up to 1.5% and 2.1% [1] allowed by the International Atomic Energy Agency for x-rays and electron radiation, respectively.
The difference between PRO field dosimeters and ARPANSA instruments ranged from 0.59% to 0.64% when measuring the x-radiation output of a given linear accelerator.
For x-rays of different energy produced by linear accelerators at each of two independent radiotherapy centres, the PRO field dosimeters differed by between 0.13% and 0.15% from independently calibrated instruments.
For a range of electron radiations and with different sets of field dosimeters, PRO field instruments differed by between 0.21% and 0.85% when used at one of the participating radiotherapy centres.
When measuring a PRO linear accelerator, for a range of electron radiations and for different sets of field dosimeters, the percentage difference of PRO dosimeters against independently-calibrated instruments ranged from 0.12% low to 0.58% high.
These results are consistent with reports from the 2008 National Dosimetry Study, which showed reference dose calibration of PRO linear accelerators were within 0.5% of the national standard.
The above positive findings justify our confidence in the sustained accuracy of linear accelerator dose calibrations at PRO and testify to the ongoing commitment of our team of medical physics professionals in providing high quality outcomes for patients.
Leonard Wee, Ph.D. MACPSEM
Senior Radiation Oncology Medical Physicist
References
[1] International Atomic Energy Agency, Technical Report Series No. 398, “Absorbed dose determination in external beam radiotherapy”, Vienna 2000.
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