A methodology for TLD postal dosimetry audit of high-energy radiotherapy photon beams in non-reference conditions.
OBJECTIVE
A strategy for national TLD audit programmes has been developed by the International Atomic Energy Agency (IAEA). It involves progression through three sequential dosimetry audit steps. The first step audits are for the beam output in reference conditions for high-energy photon beams. The second step audits are for the dose in reference and non-reference conditions on the beam axis for photon and electron beams. The third step audits involve measurements of the dose in reference, and non-reference conditions off-axis for open and wedged symmetric and asymmetric fields for photon beams. Through a co-ordinated research project the IAEA developed the methodology to extend the scope of national TLD auditing activities to more complex audit measurements for regular fields.


METHODS
Based on the IAEA standard TLD holder for high-energy photon beams, a TLD holder was developed with horizontal arm to enable measurements 5cm off the central axis. Basic correction factors were determined for the holder in the energy range between Co-60 and 25MV photon beams.


RESULTS
New procedures were developed for the TLD irradiation in hospitals. The off-axis measurement methodology for photon beams was tested in a multi-national pilot study. The statistical distribution of dosimetric parameters (off-axis ratios for open and wedge beam profiles, output factors, wedge transmission factors) checked in 146 measurements was 0.999+/-0.012.


CONCLUSIONS
The methodology of TLD audits in non-reference conditions with a modified IAEA TLD holder has been shown to be feasible.
Izewska
Joanna
J
Dosimetry and Medical Radiation Physics Section, International Atomic Energy Agency, Vienna, Austria. j.izewska@iaea.org
Georg
Dietmar
D
Bera
Pranabes
P
Thwaites
David
D
Arib
Mehenna
M
Saravi
Margarita
M
Sergieva
Katia
K
Li
Kaibao
K
Yip
Fernando Garcia
FG
Mahant
Ashok Kumar
AK
Bulski
Wojciech
W
D005240:Feasibility Studies; D006801:Humans; D007390:International Agencies; D008485:Medical Audit; D017785:Photons; D010865:Pilot Projects; D011786:Quality Control; D011874:Radiometry; D011879:Radiotherapy Dosage / Q000592:standards; D011882:Radiotherapy, High-Energy / Q000592:standards*; D012015:Reference Standards; D015203:Reproducibility of Results; D013819:Thermoluminescent Dosimetry / Q000592:standards*