National dosimetric audit network finds discrepancies in AAA lung inhomogeneity corrections.
This work presents the Australian Clinical Dosimetry Service's (ACDS) findings of an investigation of systematic discrepancies between treatment planning system (TPS) calculated and measured audit doses. Specifically, a comparison between the Anisotropic Analytic Algorithm (AAA) and other common dose-calculation algorithms in regions downstream (≥2cm) from low-density material in anthropomorphic and slab phantom geometries is presented. Two measurement setups involving rectilinear slab-phantoms (ACDS Level II audit) and anthropomorphic geometries (ACDS Level III audit) were used in conjunction with ion chamber (planar 2D array and Farmer-type) measurements. Measured doses were compared to calculated doses for a variety of cases, with and without the presence of inhomogeneities and beam-modifiers in 71 audits. Results demonstrate a systematic AAA underdose with an average discrepancy of 2.9 ± 1.2% when the AAA algorithm is implemented in regions distal from lung-tissue interfaces, when lateral beams are used with anthropomorphic phantoms. This systemic discrepancy was found for all Level III audits of facilities using the AAA algorithm. This discrepancy is not seen when identical measurements are compared for other common dose-calculation algorithms (average discrepancy -0.4 ± 1.7%), including the Acuros XB algorithm also available with the Eclipse TPS. For slab phantom geometries (Level II audits), with similar measurement points downstream from inhomogeneities this discrepancy is also not seen.
Australian Clinical Dosimetry Service, Yallambie, Victoria 3085, Australia. Electronic address: leon.dunn@austin.org.au.
Leon
L
Dunn
Australian Clinical Dosimetry Service, Yallambie, Victoria 3085, Australia; Institute of Medical Physics, University of Sydney, Sydney, Australia; School of Applied Science, RMIT University, Melbourne, Australia.
Joerg
J
Lehmann
Australian Clinical Dosimetry Service, Yallambie, Victoria 3085, Australia.
Jessica
J
Lye
Australian Clinical Dosimetry Service, Yallambie, Victoria 3085, Australia; Epworth Radiation Oncology, Richmond, Victoria 3121, Australia.
John
J
Kenny
School of Applied Science, RMIT University, Melbourne, Australia; Peter MacCallum Cancer Centre, Melbourne 3008, Australia.
Tomas
T
Kron
Australian Clinical Dosimetry Service, Yallambie, Victoria 3085, Australia.
Andrew
A
Alves
Australian Clinical Dosimetry Service, Yallambie, Victoria 3085, Australia; Australian Radiation Protection and Nuclear Safety Agency, Yallambie, Victoria 3085, Australia.
Andrew
A
Cole
North West Cancer Centre, Tamworth Hospital, Tamworth, NSW, Australia.
Jackson
J
Zifodya
Australian Clinical Dosimetry Service, Yallambie, Victoria 3085, Australia; School of Applied Science, RMIT University, Melbourne, Australia.
Ivan
I
Williams
D000465:Algorithms; D016880:Anisotropy; D001315:Australia; D006801:Humans; D008168:Lung / Q000528:radiation effects; D008485:Medical Audit; D019047:Phantoms, Imaging; D011874:Radiometry / Q000592:standards*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted
Algorithm; Audit; Dose; Dosimetry; Radiotherapy