Clinical introduction of a linac head-mounted 2D detector array based quality assurance system in head and neck IMRT

Abstract Background and purpose IMRT QA is commonly performed in a phantom geometry but the clinical interpretation of the results in a 2D phantom plane is difficult. The main objective of our work is to move from film measurement based QA to 3D dose reconstruction in a patient CT scan. In principle...

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Bibliographic Details
Published in:Radiotherapy and oncology 2011-09, Vol.100 (3), p.446-452
Main Authors: Korevaar, Erik W, Wauben, David J.L, van der Hulst, Peter C, Langendijk, Johannes A, van’t Veld, Aart A
Format: Article
Language:English
Subjects:
2D ionization chamber array
Calibration
Dose reconstruction
Film Dosimetry
Gamma index analysis
Head and Neck Neoplasms - radiotherapy
Hematology, Oncology and Palliative Medicine
Humans
IMRT QA
Particle Accelerators
Phantoms, Imaging
Quality Assurance, Health Care
Radiometry - methods
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted - methods
Radiotherapy, Intensity-Modulated - standards
Reproducibility of Results
Tomography, X-Ray Computed
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Summary:Abstract Background and purpose IMRT QA is commonly performed in a phantom geometry but the clinical interpretation of the results in a 2D phantom plane is difficult. The main objective of our work is to move from film measurement based QA to 3D dose reconstruction in a patient CT scan. In principle, this could be achieved using a dose reconstruction method from 2D detector array measurements as available in the COMPASS system (IBA Dosimetry). The first step in the clinical introduction of this system instead of the currently used film QA procedures is to test the reliability of the dose reconstruction. In this paper we investigated the validation of the method in a homogeneous phantom with the film QA procedure as a reference. We tested whether COMPASS QA results correctly identified treatment plans that did or did not fulfil QA requirements in head and neck (H&N) IMRT. Materials and methods A total number of 24 treatments were selected from an existing database with more than 100 film based H&N IMRT QA results. The QA results were classified as either good, just acceptable or clinically rejected (mean gamma index 0.5, respectively with 3%/3 mm criteria). Film QA was repeated and compared to COMPASS QA with a MatriXX detector measurement performed on the same day. Results Good agreement was found between COMPASS reconstructed dose and film measured dose in a phantom (mean gamma 0.83 ± 0.09, 1SD with 1%/1 mm criteria, 0.33 ± 0.04 with 3%/3 mm criteria). COMPASS QA results correlated well with film QA, identifying the same patients with less good QA results. Repeated measurements with film and COMPASS showed changes in delivery after a modified MLC calibration, also visible in a standard MLC check in COMPASS. The time required for QA reduced by half by using COMPASS instead of film. Conclusions Agreement of COMPASS QA results with film based QA supports its clinical introduction for a phantom geometry. A standard MLC calibration check is sensitive to
ISSN:0167-8140
1879-0887
DOI:10.1016/j.radonc.2011.09.007