Evaluation of a new VMAT QA device, or the “X” and “O” array geometries

Abstract

We introduce a logical process of three distinct phases to begin the evaluation of a new 3D dosimetry array. The array under investigation is a hollow cylinder phantom with diode detectors fixed in a helical shell forming an “O” axial detector cross section (ArcCHECK), with comparisons drawn to a previously studied 3D array with diodes fixed in two crossing planes forming an “X” axial cross section (Delta 4 ). Phase I testing of the ArcCHECK establishes: robust relative calibration (response equalization) of the individual detectors, minor field size dependency of response not present in a 2D predecessor, and uncorrected angular response dependence in the axial plane. Phase II testing reveals vast differences between the two devices when studying fixed‐width full circle arcs. These differences are primarily due to arc discretization by the TPS that produces low passing rates for the peripheral detectors of the ArcCHECK, but high passing rates for the Delta 4 . Similar, although less pronounced, effects are seen for the test VMAT plans modeled after the AAPM TG119 report. The very different 3D detector locations of the two devices, along with the knock‐on effect of different percent normalization strategies, prove that the analysis results from the devices are distinct and noninterchangeable; they are truly measuring different things. The value of what each device measures, namely their correlation with – or ability to predict – clinically relevant errors in calculation and/or delivery of dose is the subject of future Phase III work.PACS number: 87.55Qr

A retrospective analysis for patient-specific quality assurance of volumetric-modulated arc therapy plans

“…8 Many types of dosimeters have been used for patientspecific quality assurance (QA), such as ion chamber, film, 9,10 2-dimensional (2D) diode or ion chamber matrix detectors, [10][11][12][13][14] electronic portal imaging devices, 15 gel dosimetry, 16 and 3D diode arrays. 17,18 3D diode arrays are easy to use and provide 3D dose distributions and QA results, while measurements are being performed. Published studies provide evidence that 3D diode journal homepage: www.meddos.org arrays are accurate and reliable tools for dose verification of VMAT treatment.…”

Evaluation of cylindrical diode array performance for VMAT (Volumetric Arc Therapy) verification

“…[26] ArcCHECK ile alan boyutu, yön ve açısal bağımlılıklar üzerine ve sabit ark dozimetrisindeki sınırlamalar yapılan diğer çalışmalarda da gösteril-miştir. [24][25][26][27]28] Hesaplanan ve ölçülen doz karşılaştırılmasında tedavi planlamasında kullanılan doz hesaplama algoritmasının sonuçları etkileyebileceği bilinmektedir. Petoukhova ve ark.…”

Pre-treatment radiotherapy dose verification using Monte Carlo doselet modulation in a spherical phantom

“…Common approaches to perform pre-treatment dose verification include the use of ionization chamber arrays (van Esch et al 2007, Saminathan et al 2010, Godart et al 2011 and diode arrays (Feygelman et al 2011).…”