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TU‐C‐AUD B‐10: Evaluation of Accuracy of Field Size Measurements Using Profiler 2 and EPID
Author(s) -
Kurokawa C,
Fox C,
Simon T,
Ozawa S,
Li J,
Karasawa K,
Palta J
Publication year - 2008
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 - 10.1118/1.2962446
Subject(s) - ionization chamber , isocenter , optics , materials science , image resolution , detector , diode , resolution (logic) , pixel , physics , ionization , optoelectronics , ion , imaging phantom , quantum mechanics , artificial intelligence , computer science
Purpose: To evaluate the performance of two digital devices, a diode array and an EPID, for routine field size checks (normally performed by using films) by comparing with measurements using an ionization chamber. Method and Materials: Field sizes ranging from 5 × 5 cm 2 to 25 × 25 cm 2 for 6 and 18 MV photon beams were measured using the Profiler 2 (Sunnuclear) and EPID (iViewGT, Elekta) and compared with those measured with an ionization chamber in a scanning water tank. The Profiler 2 is made up of 83 diode detectors in one direction and 57 diodes in the orthogonal direction with 4 mm spacing, covering lengths of 30 cm and 20 cm in the respective two directions. The physical area of the EPID is 41 × 41 cm 2 with 1024 × 1024 pixels, resulting in a resolution of 0.25 mm projected at the isocenter. A QA jig with embedded pins was used to determine the scaling of the EPID. For each measured profile, the width at 50% of the central axis intensity was taken to be the measured field size. Results: The field sizes measured with both detectors agreed to within 1.5% of those measured with the ion chamber for both the 6 MV and 18 MV photon beams. The results for Profiler 2 are slightly better than those of the EPID although the Profiler 2 has a limited spatial resolution of 4 mm. The ratios of field sizes measured with the Profiler 2 and the EPID to those of the ion chamber are almost constant with respect to the field sizes. Conclusion: The field sizes measured with the Profiler 2 and the EPID were comparable to those using the ion chamber. They can be used for routine field size checks in place of films.