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SU‐E‐T‐645: Qualification of a 2D Ionization Chamber Array for Beam Steering and Profile Measurement
Author(s) -
Gao S,
Balter P,
Rose M,
Simon W
Publication year - 2015
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 - 10.1118/1.4925008
Subject(s) - ionization chamber , optics , linear particle accelerator , imaging phantom , beam steering , materials science , scanner , physics , beam (structure) , ionization , ion , quantum mechanics
Purpose: Establish a procedure for beam steering and profile measurement using a 2D ionization chamber array and show equivalence to a water scanning system. Methods: Multiple photon beams (30×30cm 2 field) and electron beams (25×25cm 2 cone) were steered in the radial and transverse directions using Sun Nuclear's IC PROFILER (ICP). Solid water was added during steering to ensure measurements were beyond the buildup region. With steering complete, servos were zeroed and enabled. Photon profiles were collected in a 30×30cm 2 field at dmax and 2.9 cm depth for flattened and FFF beams respectively. Electron profiles were collected with a 25×25cm 2 cone and effective depth (solid water + 0.9 cm intrinsic buildup) as follows: 0.9 cm (6e), 1.9 cm (9e), 2.9 cm (12e, 16e, 20e). Profiles of the same energy, field size and depth were measured in water with Sun Nuclear's 3D SCANNER (3DS). Profiles were re‐measured using the ICP after the in‐water scans. Profiles measured using the ICP and 3DS were compared by (a) examining the differences in Varian's “Point Difference Symmetry” metric, (b) visual inspection of the overlaid profile shapes and (c) calculation of point‐by‐point differences. Results: Comparing ICP measurements before and after water scanning showed very good agreement indicating good stability of the linac and measurement system. Comparing ICP Measurements to water phantom measurements using Varian's symmetry metric showed agreement within 0.5% for all beams. The average magnitude of the agreement was within 0.2%. Comparing ICP Measurements to water phantom measurements using point‐by‐point difference showed agreement within 0.5% inside of 80% area of the field width. Conclusion: Profile agreement to within 0.5% was observed between ICP and 3DS after steering multiple energies with the ICP. This indicates that the ICP may be used for steering electron beams, and both flattened and FFF photon beams. Song Gao: Sun Nuclear's invitation of speak and financial support for attending the 8th QA & Dosimetry Symposium in Orlando, Florida 2015.