A Bruschi1, M Esposito2, S Pini2, A Ghirelli2, G Zatelli2, S Russo3. 1. University of Florence, Italy. 2. Medical Physics Unit, Azienda USL Toscana Centro, Florence, Italy. 3. Medical Physics Unit, Azienda USL Toscana Centro, Florence, Italy. Electronic address: serenella.russo@uslcentro.toscana.it.
Abstract
PURPOSE: Aim of this work was to study how the detector resolution can affect the clinical significance of SBRT pre-treatment volumetric modulated arc therapy (VMAT) verification results. METHODS: Three detectors (PTW OCTAVIUS 4D 729, 1500 and 100 SRS) used in five configurations with different resolution were compared: 729, 729 merged, 1500, 1500 merged and 1000 SRS. Absolute local gamma passing rates of 3D pre-treatment quality assurance (QA) were evaluated for 150 dose distributions in 30 plans. Five different kinds of error were introduced in order to establish the detection sensitivity of the three devices. Percentage dosimetric differences were evaluated between planned dosevolume histogram (DVH) and patients' predicted DVH calculated by PTW DVH 4D® software. RESULTS: The mean gamma passing rates and the standard deviations were 92.4% ± 3.7%, 94.6% ± 1.8%, 95.3% ± 4.2%, 97.4% ± 2.5% and 97.6% ± 1.4 respectively for 729, 729 merged, 1500, 1500 merged and 1000 SRS with 2% local dose/2mm criterion. The same trend was found on the sensitivity analysis: using a tight gamma analysis criterion (2%L/1mm) only the 1000 SRS detected every kind of error, while 729 and 1500 merged detected three and four kinds of error respectively. Regarding dose metrics extracted from DVH curves, D50% was within the tolerance level in more than 90% of cases only for the 1000 SRS. CONCLUSIONS: The detector resolution can significantly affect the clinical significance of SBRT pre-treatment verification results. The choice of a detector with resolution suitable to the investigated field size is of main importance to avoid getting false positive.
PURPOSE: Aim of this work was to study how the detector resolution can affect the clinical significance of SBRT pre-treatment volumetric modulated arc therapy (VMAT) verification results. METHODS: Three detectors (PTW OCTAVIUS 4D 729, 1500 and 100 SRS) used in five configurations with different resolution were compared: 729, 729 merged, 1500, 1500 merged and 1000 SRS. Absolute local gamma passing rates of 3D pre-treatment quality assurance (QA) were evaluated for 150 dose distributions in 30 plans. Five different kinds of error were introduced in order to establish the detection sensitivity of the three devices. Percentage dosimetric differences were evaluated between planned dosevolume histogram (DVH) and patients' predicted DVH calculated by PTW DVH 4D® software. RESULTS: The mean gamma passing rates and the standard deviations were 92.4% ± 3.7%, 94.6% ± 1.8%, 95.3% ± 4.2%, 97.4% ± 2.5% and 97.6% ± 1.4 respectively for 729, 729 merged, 1500, 1500 merged and 1000 SRS with 2% local dose/2mm criterion. The same trend was found on the sensitivity analysis: using a tight gamma analysis criterion (2%L/1mm) only the 1000 SRS detected every kind of error, while 729 and 1500 merged detected three and four kinds of error respectively. Regarding dose metrics extracted from DVH curves, D50% was within the tolerance level in more than 90% of cases only for the 1000 SRS. CONCLUSIONS: The detector resolution can significantly affect the clinical significance of SBRT pre-treatment verification results. The choice of a detector with resolution suitable to the investigated field size is of main importance to avoid getting false positive.
Authors: Esther Decabooter; Ans Cc Swinnen; Michel C Öllers; Fabian Göpfert; Frank Verhaegen Journal: Br J Radiol Date: 2021-06-11 Impact factor: 3.629
Authors: James McCulloch; Jamie Pawlowski; Neil Kirby; Karl Rasmussen; Zheng Shi; Pamela Myers; Sotirios Stathakis; Niko Papanikolaou; Daniel L Saenz Journal: J Appl Clin Med Phys Date: 2020-07-18 Impact factor: 2.102