Program Information
Qualification of a 2D Ionization Chamber Array for Beam Steering and Profile Measurement
S Gao1*, P Balter2 , M Rose3 , W Simon4 , (1) MD Anderson Cancer Ctr., Houston, TX, (2) UT MD Anderson Cancer Center, Houston, TX, (3) Sun Nuclear Inc., Melbourne, FL, (4) Sun Nuclear Corp, Melbourne, FL
Presentations
SU-E-T-645 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
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 (30x30cm² field) and electron beams (25x25cm² 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 30x30cm² field at dmax and 2.9 cm depth for flattened and FFF beams respectively. Electron profiles were collected with a 25x25cm² 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.
Funding Support, Disclosures, and Conflict of Interest: Song Gao: Sun Nuclear's invitation of speak and financial support for attending the 8th QA & Dosimetry Symposium in Orlando, Florida 2015.
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