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TH‐D‐224C‐03: Integral Test Phantom For Dosimetric and Geometric Assurance of IG‐IMRT
Author(s) -
Letourneau D,
Moseley D,
Sharpe M,
Jaffray D
Publication year - 2006
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 - 10.1118/1.2241916
Subject(s) - imaging phantom , isocenter , quality assurance , ionization chamber , image quality , nuclear medicine , dosimetry , medical imaging , diode , cone beam computed tomography , radiation treatment planning , optics , radiation therapy , materials science , physics , medicine , computed tomography , radiology , computer science , image (mathematics) , optoelectronics , external quality assessment , pathology , ion , quantum mechanics , artificial intelligence , ionization
Purpose: To develop a combined imaging and dosimetric phantom for the quality assurance (QA) of linear accelerators capable of cone‐beam CT image‐guided and intensity modulated radiotherapy (IG‐IMRT). This integrated approach verifies image quality, registration, and delivery performance. Method and Materials: The prototype consisted of a cylindrical imaging phantom (CatPhan) combined with an array of 11 radiation diodes arranged in a plane, oriented perpendicular to the phantom axis. Single diode performance was assessed at 6 and 18 MV (profiles, depth‐dose curves and angular dependence) with comparison to ion chamber. The detection of geometric and dosimetric errors in delivery was assessed using an IG‐IMRT treatment (6 MV, 7 beams, 180 cGy, CBCT‐guided) in which known displacements relative to isocenter were applied. The minimum detectable shift was determined by comparing the discrepancy between planned and measured doses to the dose measurement uncertainty under non‐shifted conditions. Results: Diode profiles and depth dose curves agreed generally within ±1% with the chamber results. Angular dependence for the diode was low for axial beams (±1%) but increased to a maximum of 11% for out‐of‐plane irradiation. The normalized dose measurements obtained with the multi‐diode phantom agreed well with the planning results. Displacements as small as 1 mm resulted in detectable deviation dose (8.2 cGy SD, n=11) relative to the uncertainty in dose measurements for non‐shifted conditions (1.6 cGy SD, n=11). Conclusion: A phantom prototype was designed and constructed for comprehensive QA of image‐guided radiotherapy in terms of image quality and dose delivery. The results allow us to set specifications for further development. We anticipate the system will permit the localization/detection of sub‐millimeters errors in dose gradient placement. Future phantom designs will facilitate absolute dosimetry and investigate the use of additional diodes in different patterns. Conflict of Interest: Supported in part by Sun Nuclear Corporation and Elekta Inc.