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SU‐E‐T‐262: Quality Assurance on Field Size Shaped by Iris Collimator of the CyberKnife
Author(s) -
Wong F,
Chow T
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3612213
Subject(s) - collimator , cyberknife , beam (structure) , optics , dosimetry , laser beam quality , collimated light , image resolution , quality assurance , physics , materials science , radiosurgery , nuclear medicine , engineering , medicine , laser , radiation therapy , laser beams , operations management , external quality assessment
Purpose: To develop a simple method to measure the x‐ray beam field size shaped by the iris collimator of the CyberKnife. Methods: The profile of the 12‐sided polygonal beam shaped by iris collimator of the Cyberknife (Accuray) was obtained using a single array beam profiler (Sun Nuclear, Model: 1170, spatial resolution = 5 mm). To improve the resolution of the profile, we moved the x‐ray beam along the array of diodes on the profiler and obtained beam profiles for every 1 mm. The beam profiles were then shifted according to their positions relative to the starting position and created an integrated beam profile. Since there are 6 different axes on the 12‐sided polygonal beam, we can obtain the beam profiles on the other five axes in a similar fashion, by simply rotating the head of the CyberKnife. This method was also examined by replacing the beam profiler with an IˈmRT MatriXX (IBA Dosimetry). Results: By using the beam profiler, we measured the field sizes of different iris collimator setting (from 10 to 60 mm). We found that the measured field sizes are within +/− 0.4 mm compared to the expected field size. Also, we found that the variation of measured field sizes is within +/− 0.2 mm between measurements. By using the IˈmRT MatriXX, we found that the uncertainty of the measured field size now increases to +/− 1 mm. Conclusions: The method of using the beam profiler is a feasible and easy way to check the consistency of the field size shaped by the iris collimator, and reduces the reliance on using radiochromic film and water phantom. We are also investigating the feasibility of using dose area product (DAP) measured by parallel plate chamber to verify field sizes in daily QA.