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Megavoltage Photon TLD Audit Service

ARPANSA offers a mailed thermoluminescence dosimetry (TLD) audit service for megavoltage (MV) photon beams to all radiotherapy providers in Australia and New Zealand.

Introduction

The Australasian College of Physical Scientists and Engineers in Medicine (ACPSEM) considers a radiotherapy dosimetry audit service to be vital for radiation oncology. The Tripartite Committee of the ACPSEM, the Australian Institute of Radiography (AIR) and the Royal Australian and New Zealand College of Radiologists (RANZCR) has suggested that quality assurance testing should be performed to at least Level 1 at regular intervals.

Audit Measurements

Participating centres are mailed a number of TLD capsules and an irradiation jig for convenient experimental setup. Two measurements of each MV photon beam are possible:

  1. Beam output – The capsule is positioned at reference depth (usually 10 cm) in a water phantom and irradiated with a dose of 2 Gy.
  2. Beam quality – Capsules are irradiated at depths of 10 cm and 20 cm in a water phantom for TPR20,10 or D20,10 determination.

Dose Evaluation

After being returned to ARPANSA, the dose to each capsule is determined by comparing its response to the response of control capsules. These are irradiated at ARPANSA with known doses traceable to the Australian primary standard of absorbed dose. A number of correction factors are also included for final dose determination as shown below.

DH = (RH / RC) DC klin kengy kfad khol

DH = dose to capsule irradiated at participating centre
RH = response of capsule irradiated at participating centre
RC = response of control capsule irradiated at ARPANSA
DC = known dose delivered to control capsule at ARPANSA
klin = non-linearity dose response correction factor
kengy = energy correction factor
kfad = fading correction factor
khol = TLD holder correction factor

After evaluation, the participating centre will be provided with a written report detailing the difference between the beam output/quality stated for each beam compared to the ARPANSA measured beam output/quality.

For further information on the audit process or to indicate your desire to participate, please contact Chris Oliver.

Contact

Dr Chris Oliver
Phone: +61 3 9433 2333

 

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