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Pretreatment Patient Clinical Objective IMRT Quality Assurance Using a 3D Diode Array

L Ren

L Ren*, Y Zhang, Y Yang, J Adamson, F Yin, Duke University Medical Center, Durham, NC

SU-E-T-196 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate the accuracy and sensitivity of a patient clinical objective IMRT QA tool using a 3D diode array.

Methods: A 3D QA device (Delta4, Scandidos Inc.) with 2 orthogonal diode array planes was used for IMRT QA. The diode spacing is 5mm in central 6cmx6cm region and 1cm in the peripheral 20cmx20cm region. 3D volumetric dose is interpolated from the measured planar dose. The Delta4 Anatomy software (Anatomy) calculates the entrance energy fluence for each beam, which is then applied to the patient anatomy to calculate dose to the patient using a pencil-beam dose calculation algorithm. The accuracy of Anatomy was evaluated in both solid water phantom using open fields and in patient anatomy using a prostate IMRT plan. The dose calculated by Eclipse was used as the gold standard. The sensitivity of the Anatomy was also evaluated by introducing leaf positioning errors in the delivery of a spine SBRT plan.

Results: Excellent agreement between Anatomy and Eclipse was achieved for the solid water phantom with open fields. Discrepancy was observed for the PTV DVH calculated in patient anatomy using the prostate IMRT plan. This is mainly due to sharp dose fall-off outside PTV and phantom setup errors during QA. Good agreement between Anatomy and Eclipse was achieved for bladder and rectum DVH. For spine case with introduced 1cm single leaf positioning error, the traditional gamma analysis using Delta4 still showed 95% pass rate using 3%, 3mm criteria. However, Anatomy showed 40% increase of cord max dose due to this error, which was consistent with Eclipse.

Conclusion: Patient clinical objective QA using Delta4 Anatomy can potentially provide valuable information about the clinical significance of the QA results. It can potentially catch clinically significant delivery errors that would otherwise be missed in the traditional QA process using gamma analysis.

Funding Support, Disclosures, and Conflict of Interest: Funding from Scandidos Inc.

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