Weekly verification of dosimetric data for virtual wedge using a 2D diode detector array.
A linac manufacturer has recommended that users measure virtual wedge (VW) angle and VW factor as a weekly quality assurance (QA) procedure. The purpose of this study was to investigate whether a 2D diode detector array (MapCHECK™) is a useful tool for the verification of dosimetric data for VW. Measurements were performed on 2 linear accelerators (4, 6, and 10 MV) at 10-cm depth for a field size of 10 × 10 cm(2) and with wedge angles of 15, 30, 45, and 60°. To verify the VW dose distributions generated by the treatment planning system (TPS), we confirmed that agreement between TPS data and measurements were ≤ 2% dose difference or 2-mm distance-to-agreement based on American Association of Physicists in Medicine Task Group Report 53 (AAPM TG-53). We present here the results of a 1-year evaluation of VW by means of a 2D diode detector array. The maximum 2-fold standard deviation of the measured wedge angle turned out to be within 1.0, and all measured VW factors to be 1.00 ± 0.03. Although >95% of the points measured for 6 and 10 MV were generally within the tolerance of the dose distribution as mentioned above, the percentage of agreement between the measured data for 4 MV and TPS data were somewhat below 90%. We also verified generally good reproducibility for the dose distribution. The 2-D diode detector array was thus found to be useful as a tool for weekly VW QA.
Department of Radiation Oncology, Osaka University Graduate School of Medicine, Osaka, Japan. ogata@radonc.med.osaka-u.ac.jp
Toshiyuki
T
Ogata
Masahiko
M
Koizumi
Iori
I
Sumida
Yutaka
Y
Takahashi
Yuichi
Y
Akino
Fumiaki
F
Isohashi
Koji
K
Konishi
Yasuo
Y
Yoshioka
Takehiro
T
Inoue
D006801:Humans; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation*