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Title: Source position verification and dosimetry in HDR brachytherapy using an EPID

Purpose: Accurate treatment delivery in high dose rate (HDR) brachytherapy requires correct source dwell positions and dwell times to be administered relative to each other and to the surrounding anatomy. Treatment delivery inaccuracies predominantly occur for two reasons: (i) anatomical movement or (ii) as a result of human errors that are usually related to incorrect implementation of the planned treatment. Electronic portal imaging devices (EPIDs) were originally developed for patient position verification in external beam radiotherapy and their application has been extended to provide dosimetric information. The authors have characterized the response of an EPID for use with an {sup 192}Ir brachytherapy source to demonstrate its use as a verification device, providing both source position and dosimetric information.Methods: Characterization of the EPID response using an {sup 192}Ir brachytherapy source included investigations of reproducibility, linearity with dose rate, photon energy dependence, and charge build-up effects associated with exposure time and image acquisition time. Source position resolution in three dimensions was determined. To illustrate treatment verification, a simple treatment plan was delivered to a phantom and the measured EPID dose distribution compared with the planned dose.Results: The mean absolute source position error in the plane parallel to the EPID, for dwells measuredmore » at 50, 100, and 150 mm source to detector distances (SDD), was determined to be 0.26 mm. The resolution of the z coordinate (perpendicular distance from detector plane) is SDD dependent with 95% confidence intervals of ±0.1, ±0.5, and ±2.0 mm at SDDs of 50, 100, and 150 mm, respectively. The response of the EPID is highly linear to dose rate. The EPID exhibits an over-response to low energy incident photons and this nonlinearity is incorporated into the dose calibration procedure. A distance (spectral) dependent dose rate calibration procedure has been developed. The difference between measured and planned dose is less than 2% for 98.0% of pixels in a two-dimensional plane at an SDD of 100 mm.Conclusions: Our application of EPID dosimetry to HDR brachytherapy provides a quality assurance measure of the geometrical distribution of the delivered dose as well as the source positions, which is not possible with any current HDR brachytherapy verification system.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ; ;  [4] ;  [5] ;  [2]
  1. William Buckland Radiation Oncology, Alfred Health, Melbourne 3004, Australia and School of Applied Sciences and Health Innovations Research Institute, RMIT University, Melbourne 3001 (Australia)
  2. William Buckland Radiation Oncology, Alfred Health, Melbourne 3004 (Australia)
  3. (Australia)
  4. School of Applied Sciences and Health Innovations Research Institute, RMIT University, Melbourne 3001 (Australia)
  5. School of Applied Sciences and Health Innovations Research Institute, RMIT University, Melbourne 3001, Australia and Physical Sciences, Peter MacCallum Cancer Centre, East Melbourne 3002 (Australia)
Publication Date:
OSTI Identifier:
22220248
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 40; Journal Issue: 11; Other Information: (c) 2013 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
61 RADIATION PROTECTION AND DOSIMETRY; 62 RADIOLOGY AND NUCLEAR MEDICINE; ANATOMY; BRACHYTHERAPY; CALIBRATION; DOSE RATES; DOSIMETRY; ERRORS; IMAGE PROCESSING; IRIDIUM 192; PHANTOMS; QUALITY ASSURANCE; RADIATION DOSE DISTRIBUTIONS; VERIFICATION