AbstractID: 7457 Title: Verification of IMRT Delivery Using a 2-D...

AbstractID: 7457 Title: Verification of IMRT Delivery Using a 2-D Diode Array and Analysis Software
Verification of IMRT delivery requires a balance of efficiency, dosimetric accuracy, and completeness. While film measurements
provide completeness, the processing time and dosimetry methods are not efficient. Ionization micro-chambers provide excellent
absolute dosimetry, but it is impractical to measure enough single points to establish the correctness of a complex IMRT field. In this
work, we examine the efficacy of using a two-dimensional diode array for IMRT delivery verification. The array covers a 22 cm x 22
cm measurement plane using 445 individual diodes. These diodes show an excellent linear response to dose. Operating in integration
mode allows for dosimetric verification of static (compensator-based) modulation and MLC-based (step-and-shoot or dynamic)
modulation. For each IMRT field, we measured absolute planar dose in phantom, and we replicated the delivery with the IMRT
treatment planning system to produce QA absolute dose planes. We built an analysis tool that imports the calibrated diode
measurements, along with the 1 mm-resolution calculated QA dose planes. This tool analyzes each diode position vs. corresponding
calculated values for percent difference and distance-to-agreement criteria. Resulting statistical analyses are performed with userspecified acceptance criteria, and visualization techniques show the dose plane as a grayscale “virtual film” with superimposed colorcoded symbols at any diode positions that fail the acceptance criteria. The time needed to measure, calculate, and analyze delivery for
a five-beam IMRT plan was 15 minutes. The proposed method of IMRT delivery verification proved efficient, accurate, and
Research partially supported by Computerized Medical Systems, Inc. and Sun Nuclear Corporation.
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