N-isopropylacrylamide gel dosimeter to evaluate clinical photon beam characteristics.
The introduction of beam intensity control concept in current radiotherapy techniques has increased treatment planning complexity. Thus, small-field dose measurement has become increasingly vital. Polymer gel dosimetry method is widely studied. It is the only dose measurement tool that provides 3D dose distribution. This study aims to use an N-isopropylacrylamide (NIPAM) gel dosimeter to conduct beam performance measurements of percentage depth dose (PDD), beam flatness, and symmetry for photon beams with field sizes of 3×3 and 4×4 cm(2). Computed tomography scans were used to readout the gel dosimeters. In the PDD measurement, the NIPAM gel dosimeter and Gafchromic™ EBT3 radiochromic film displayed high consistency in the region deeper than the build-up region. The gel dosimeter dose profile had 3% lower flatness and symmetry measurement at 5 cm depth for different fields compared with that of the Gafchromic™ EBT3 film. During gamma evaluation under 3%/3 mm dose difference/distance-to-agreement standard, the pass rates of the polymer gel dosimeter to the TPS and EBT3 film were both higher than 96%. Given that the gel is tissue equivalent, it did not exhibit the energy dependence problems of radiochromic films. Therefore, the practical use of NIPAM polymer gel dosimeters is enhanced in clinical dose verification.
Department of Radiation Oncology, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chia-Yi, Taiwan, ROC; Department of Medical Imaging and Radiological Science, Central Taiwan University of Science and Technology, No. 666, Buzih Road., Beitun District, Taichung City 40601, Taiwan, ROC.
Chung-Yu
CY
Chiu
Department of Radiation Oncology, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chia-Yi, Taiwan, ROC.
Yuk-Wah
YW
Tsang
Department of Medical Imaging and Radiological Science, Central Taiwan University of Science and Technology, No. 666, Buzih Road., Beitun District, Taichung City 40601, Taiwan, ROC. Electronic address: bthsieh@ctust.edu.tw.
Bor-Tsung
BT
Hsieh
D000178:Acrylamides / Q000737:chemistry* / Q000528:radiation effects*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005782:Gels / Q000737:chemistry / Q000528:radiation effects; D017785:Photons / Q000627:therapeutic use*; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D000178:Acrylamides; D005782:Gels; C067295:N-isopropylacrylamide
Flatness; Percentage depth dose (PDD); Polymer gel dosimeter; Symmetry