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      Influence of the jaw tracking technique on the dose calculation accuracy of small field VMAT plans

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          Abstract

          Purpose

          The aim of this study was to evaluate experimentally the accuracy of the dose calculation algorithm AcurosXB in small field highly modulated Volumetric Modulated Arc Therapy (VMAT).

          Method

          The 1000SRS detector array inserted in the rotational Octavius 4D phantom (PTW) was used for 3D dose verification of VMAT treatments characterized by small to very small targets. Clinical treatment plans ( n = 28) were recalculated on the phantom CT data set in the Eclipse TPS. All measurements were done on a Varian TrueBeamSTx, which can provide the jaw tracking technique (JTT). The effect of disabling the JTT, thereby fixing the jaws at static field size of 3 × 3 cm 2 and applying the MLC to shape the smallest apertures, was investigated for static fields between 0.5 × 0.5−3 × 3 cm 2 and for seven VMAT patients with small brain metastases. The dose calculation accuracy has been evaluated by comparing the measured and calculated dose outputs and dose distributions. The dosimetric agreement has been presented by a local gamma evaluation criterion of 2%/2 mm.

          Results

          Regarding the clinical plans, the mean ± SD of the volumetric gamma evaluation scores considering the dose levels for evaluation of 10%, 50%, 80% and 95% are (96.0 ± 6.9)%, (95.2 ± 6.8)%, (86.7 ± 14.8)% and (56.3 ± 42.3)% respectively. For the smallest field VMAT treatments, discrepancies between calculated and measured doses up to 16% are obtained. The difference between the 1000SRS central chamber measurements compared to the calculated dose outputs for static fields 3 × 3, 2 × 2, 1 × 1 and 0.5 × 0.5 cm 2 collimated with MLC whereby jaws are fixed at 3 × 3 cm 2 and for static fields shaped with the collimator jaws only (MLC retracted), is on average respectively, 0.2%, 0.8%, 6.8%, 5.7% (6 MV) and 0.1%, 1.3%, 11.7%, 21.6% (10 MV). For the seven brain mets patients was found that the smaller the target volumes, the higher the improvement in agreement between measured and calculated doses after disabling the JTT.

          Conclusion

          Fixing the jaws at 3 × 3 cm 2 and using the MLC with high positional accuracy to shape the smallest apertures in contrast to the JTT is currently found to be the most accurate treatment technique.

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          Most cited references25

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          A technique for the quantitative evaluation of dose distributions.

          The commissioning of a three-dimensional treatment planning system requires comparisons of measured and calculated dose distributions. Techniques have been developed to facilitate quantitative comparisons, including superimposed isodoses, dose-difference, and distance-to-agreement (DTA) distributions. The criterion for acceptable calculation performance is generally defined as a tolerance of the dose and DTA in regions of low and high dose gradients, respectively. The dose difference and DTA distributions complement each other in their useful regions. A composite distribution has recently been developed that presents the dose difference in regions that fail both dose-difference and DTA comparison criteria. Although the composite distribution identifies locations where the calculation fails the preselected criteria, no numerical quality measure is provided for display or analysis. A technique is developed to unify dose distribution comparisons using the acceptance criteria. The measure of acceptability is the multidimensional distance between the measurement and calculation points in both the dose and the physical distance, scaled as a fraction of the acceptance criteria. In a space composed of dose and spatial coordinates, the acceptance criteria form an ellipsoid surface, the major axis scales of which are determined by individual acceptance criteria and the center of which is located at the measurement point in question. When the calculated dose distribution surface passes through the ellipsoid, the calculation passes the acceptance test for the measurement point. The minimum radial distance between the measurement point and the calculation points (expressed as a surface in the dose-distance space) is termed the gamma index. Regions where gamma > 1 correspond to locations where the calculation does not meet the acceptance criteria. The determination of gamma throughout the measured dose distribution provides a presentation that quantitatively indicates the calculation accuracy. Examples of a 6 MV beam penumbra are used to illustrate the gamma index.
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            An efficient protocol for radiochromic film dosimetry combining calibration and measurement in a single scan.

            Radiochromic film provides dose measurement at high spatial resolution, but often is not preferred for routine evaluation of patient-specific intensity modulated radiation therapy (IMRT) plans owing to ease-of-use factors. The authors have established an efficient protocol that combines calibration and measurement in a single scan and enables measurement results to be obtained in less than 30 min. This avoids complications due to postexposure changes in radiochromic film that delay the completion of a measurement, often for up to 24 h, in commonly used methods. In addition, the protocol addresses the accuracy and integrity of the measurement by eliminating environmental and interscan variability issues.
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              • Abstract: found
              • Article: not found

              A quantitative evaluation of IMRT dose distributions: refinement and clinical assessment of the gamma evaluation.

              Although intensity modulated radiotherapy (IMRT) is a step forward in comparison to conventional, static beam delivery, quality assurance is more complex and labour intensive, demanding detailed two-dimensional dosimetric verification. Regardless of the technique used for measuring the dose distribution, what is essential to the implementation of routine verification of IMRT fields is the efficient and accurate comparison of the measured versus desired dose distribution. In order to achieve a fast, yet accurate quantitative measure of the correspondence between measured and calculated dose, the theoretical concept of the gamma evaluation method presented by Low et al. (Med. Phys., 25 (1998) 656) was converted into a calculation algorithm, taking into account practical considerations related to the discrete nature of the data. A filter cascade of multiple levels was designed to obtain fast and accurate comparison of the two dose distributions under evaluation. The actual comparison consists of classification into accepted or rejected datapoints with respect to user-defined acceptance criteria (dose difference and distance to agreement). The presented algorithm was tested on dosimetric images calculated and/or acquired by means of a liquid filled portal imaging device during the course of intensity modulated treatments of prostate cancer, including pre-treatment verification as well as verification during treatment. To assess its ability to intercept possible errors in dose delivery, clinically relevant errors were deliberately introduced into the dose distributions. The developed gamma filter method proves successful in the efficient comparison of calculated versus measured IMRT dose distribution. Secondly, intercomparison of dosimetric images acquired during different treatment sessions illustrate its potential to highlight variations in the dosimetric images. The simulated errors were unmistakably intercepted. The readily obtained gamma evaluation images are an easy tool for quality control of IMRT fields. To reduce the artefacts related to the discrete nature and limited resolution of the data, a fast and accurate filter cascade was developed, offering the possibility to use the gamma method for day to day evaluation of patient dosimetric portal images with or without comparison to a predicted portal dose distribution.
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                Author and article information

                Contributors
                ans.swinnen@maastro.nl
                Journal
                J Appl Clin Med Phys
                J Appl Clin Med Phys
                10.1002/(ISSN)1526-9914
                ACM2
                Journal of Applied Clinical Medical Physics
                John Wiley and Sons Inc. (Hoboken )
                1526-9914
                03 January 2017
                January 2017
                : 18
                : 1 ( doiID: 10.1002/acm2.2017.18.issue-1 )
                : 186-195
                Affiliations
                [ 1 ] Radiotherapy Department Maastro Clinic 6229 ET Maastricht The Netherlands
                Author notes
                [*] [* ] Author to whom correspondence should be addressed. Ans C.C. Swinnen

                E‐mail: ans.swinnen@ 123456maastro.nl ;

                Telephone: 0031 88 4455571.

                Article
                ACM212029
                10.1002/acm2.12029
                5689875
                28291941
                57ba1938-e91d-4c49-a820-11295903adf5
                © 2017 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 07 November 2016
                : 07 November 2016
                : 21 November 2016
                Page count
                Figures: 3, Tables: 3, Pages: 10, Words: 8943
                Categories
                87.53.Bn
                Radiation Oncology Physics
                Radiation Oncology Physics
                Custom metadata
                2.0
                acm212029
                January 2017
                Converter:WILEY_ML3GV2_TO_NLMPMC version:5.2.5 mode:remove_FC converted:16.11.2017

                calculation algorithm,dosimetry,jaw tracking technique,small fields

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