Assessing the suitability of a two-dimensional array for routine quality assurance checks of flatness and symmetry
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SCIENTIFIC NOTE
Assessing the suitability of a two‑dimensional array for routine quality assurance checks of flatness and symmetry Salma Ibrahim1 · Venkatakrishnan Seshadri1 · Paul Charles2,3 Received: 4 September 2019 / Accepted: 25 September 2020 © Australasian College of Physical Scientists and Engineers in Medicine 2020
Abstract Quality assurance of radiotherapy linear accelerator beams demands the use of equipment with high resolution and reliability of reproducible results over time. This study examines the suitability of a commercially available two-dimensional ionization chamber array—the StarCheck array (PTW, Frieburg, Germany) to measure symmetry and flatness for both photon and electron beams. The study was conducted over a period of 4 years whereby the reliability of the array could be established. The reproducibility, uniformity of chamber response, and comparison of both photon and electron profiles acquired with the StarCheck array to that of the water-tank were examined. The most significant result was that across all profiles acquired using the StarCheck array, a defective chamber was detected, manifested by a ‘dip’ in the cross-plane profile at the same position. Assuming all detectors are functional, StarCheck was shown to be within 1% of the water-tank results for both flatness and symmetry. The detector array exhibited many calibration and detector issues over the period in which it has been used in the department. Furthermore, PTW recommends that recalibration of the array should to be performed every 2 years at either PTW, Freiburg, or at a qualified calibration laboratory. Therefore, the department requires a backup device for the recalibration time, approximately 4 months as worst case. Keywords PTW StarCheck · Routine quality assurance · Symmetry and flatness
Introduction During initial commissioning and annual quality assurance (QA) of a medical linear accelerator (LINAC), beam profiles are usually acquired carefully using a computer-controlled water-tank system. The set-up procedure of the water-tank for the measurements of flatness and symmetry consumes a great amount of machine and personnel time for the required accuracy, and it is unlikely that a busy radiotherapy department will have the resources to set it up on a routine monthly basis. For this reason, many two-dimensional detector arrays have been made commercially available to be used for routine QA measurements. Because complex treatments (such
* Salma Ibrahim [email protected] 1
Princess Alexandra Hospital, Woolloongabba, QLD, Australia
2
Science and Engineering Faculty, Queensland University of Technology, Brisbane, QLD, Australia
3
Herston Biofabrication Institute, Brisbane, QLD, Australia
as intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT)) demand more QA, reducing the overhead for any particular quality control (QC) task is advantageous as it allows for more attention on higher risk aspects of the system [1]. The use of an ion chamber array for assessin
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