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      Verification of high-dose-rate brachytherapy treatment planning dose distribution using liquid-filled ionization chamber array

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          Abstract

          Purpose

          This study aims to investigate the dosimetric performance of a liquid-filled ionization chamber array in high-dose-rate (HDR) brachytherapy dosimetry. A comparative study was carried out with air-filled ionization chamber array and EBT3 Gafchromic films to demonstrate its suitability in brachytherapy.

          Material and methods

          The PTW OCTAVIUS detector 1000 SRS (IA 2.5-5 mm) is a liquid-filled ionization chamber array of area 11 x 11 cm 2 and chamber spacing of 2.5-5 mm, whereas the PTW OCTAVIUS detector 729 (IA 10 mm) is an air vented ionization chamber array of area 27 x 27 cm 2 and chamber spacing of 10 mm. EBT3 films were exposed to doses up to a maximum of 6 Gy and evaluated using multi-channel analysis. The detectors were evaluated using test plans to mimic a HDR intracavitary gynecological treatment. The plan was calculated and delivered with the applicator plane placed 20 mm from the detector plane. The acquired measurements were compared to the treatment plan. In addition to point dose measurement, profile/isodose, gamma analysis, and uncertainty analysis were performed. Detector sensitivity was evaluated by introducing simulated errors to the test plans.

          Results

          The mean point dose differences between measured and calculated plans were 0.2% ± 1.6%, 1.8% ± 1.0%, and 1.5% ± 0.81% for film, IA 10 mm, and IA 2.5-5 mm, respectively. The average percentage of passed gamma (global/local) values using 3%/3 mm criteria was above 99.8% for all three detectors on the original plan. For IA 2.5-5 mm, local gamma criteria of 2%/1 mm with a passing rate of at least 95% was found to be sensitive when simulated positional errors of 1 mm was introduced.

          Conclusion

          The dosimetric properties of IA 2.5-5 mm showed the applicability of liquid-filled ionization chamber array as a potential QA device for HDR brachytherapy treatment planning systems.

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          Most cited references46

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          American Association of Physicists in Medicine Radiation Therapy Committee Task Group 53: quality assurance for clinical radiotherapy treatment planning.

          B Fraass, K. Doppke, M. Hunt … (1998)
          In recent years, the sophistication and complexity of clinical treatment planning and treatment planning systems has increased significantly, particularly including three-dimensional (3D) treatment planning systems, and the use of conformal treatment planning and delivery techniques. This has led to the need for a comprehensive set of quality assurance (QA) guidelines that can be applied to clinical treatment planning. This document is the report of Task Group 53 of the Radiation Therapy Committee of the American Association of Physicists in Medicine. The purpose of this report is to guide and assist the clinical medical physicist in developing and implementing a comprehensive but viable program of quality assurance for modern radiotherapy treatment planning. The scope of the QA needs for treatment planning is quite broad, encompassing image-based definition of patient anatomy, 3D beam descriptions for complex beams including multileaf collimator apertures, 3D dose calculation algorithms, and complex plan evaluation tools including dose volume histograms. The Task Group recommends an organizational framework for the task of creating a QA program which is individualized to the needs of each institution and addresses the issues of acceptance testing, commissioning the planning system and planning process, routine quality assurance, and ongoing QA of the planning process. This report, while not prescribing specific QA tests, provides the framework and guidance to allow radiation oncology physicists to design comprehensive and practical treatment planning QA programs for their clinics.
          Article 0 comments Cited 185 times – based on 0 reviews     Review now
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            Computed tomography versus magnetic resonance imaging-based contouring in cervical cancer brachytherapy: results of a prospective trial and preliminary guidelines for standardized contours.

            Christian Kirisits, Johannes Carl Athanasios Dimopoulos, Richard Pötter … (2007)
            To compare the contours and dose-volume histograms (DVH) of the tumor and organs at risk (OAR) with computed tomography (CT) vs. magnetic resonance imaging (MRI) in cervical cancer brachytherapy. Ten patients underwent both MRI and CT after applicator insertion. The dose received by at least 90% of the volume (D(90)), the minimal target dose (D(100)), the volume treated to the prescription dose or greater for tumor for the high-risk (HR) and intermediate-risk (IR) clinical target volume (CTV) and the dose to 0.1 cm3, 1 cm3, and 2 cm3 for the OARs were evaluated. A standardized approach to contouring on CT (CT(Std)) was developed, implemented (HR- and IR-CTV(CTStd)), and compared with the MRI contours. Tumor height, thickness, and total volume measurements, as determined by either CT or CT(Std) were not significantly different compared with the MRI volumes. In contrast, the width measurements differed in HR-CTV(CTStd) (p = 0.05) and IR-CTV(CTStd) (p = 0.01). For the HR-CTV(CTStd), this resulted in statistically significant differences in the volume treated to the prescription dose or greater (MRI, 96% vs. CT(Std), 86%, p = 0.01), D(100) (MRI, 5.4 vs. CT(Std), 3.4, p <0.01), and D(90) (MRI, 8.7 vs. CT(Std), 6.7, p <0.01). Correspondingly, the IR-CTV DVH values on MRI vs. CT(Std), differed in the D(100) (MRI, 3.0 vs. CT(Std), 2.2, p = 0.01) and D(90) (MRI, 5.6 vs. CT(Std), 4.6, p = 0.02). The MRI and CT DVH values of the dose to 0.1 cm3, 1 cm3, and 2 cm3 for the OARs were similar. Computed tomography-based or MRI-based scans at brachytherapy are adequate for OAR DVH analysis. However, CT tumor contours can significantly overestimate the tumor width, resulting in significant differences in the D(90), D(100), and volume treated to the prescription dose or greater for the HR-CTV compared with that using MRI. MRI remains the standard for CTV definition.
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              Multichannel film dosimetry with nonuniformity correction.

              Andre Micke, David F Lewis, Xiang Yu (2011)
              A new method to evaluate radiochromic film dosimetry data scanned in multiple color channels is presented. This work was undertaken to demonstrate that the multichannel method is fundamentally superior to the traditional single channel method. The multichannel method allows for the separation and removal of the nondose-dependent portions of a film image leaving a residual image that is dependent only on absorbed dose. Radiochromic films were exposed to 10 x 10 cm radiation fields (Co-60 and 6 MV) at doses up to about 300 cGy. The films were scanned in red-blue-green (RGB) format on a flatbed color scanner and measured to build calibration tables relating the absorbed dose to the response of the film in each of the color channels. Film images were converted to dose maps using two methods. The first method used the response from a single color channel and the second method used the response from all three color channels. The multichannel method allows for the separation of the scanned signal into one part that is dose-dependent and another part that is dose-independent and enables the correction of a variety of disturbances in the digitized image including nonuniformities in the active coating on the radiochromic film as well as scanner related artifacts. The fundamental mathematics of the two methods is described and the dose maps calculated from film images using the two methods are compared and analyzed. The multichannel dosimetry method was shown to be an effective way to separate out non-dose-dependent abnormalities from radiochromic dosimetry film images. The process was shown to remove disturbances in the scanned images caused by nonhomogeneity of the radiochromic film and artifacts caused by the scanner and to improve the integrity of the dose information. Multichannel dosimetry also reduces random noise in the dose images and mitigates scanner-related artifacts such as lateral position dependence. In providing an ability to calculate dose maps from data in all the color channels the multichannel method provides the ability to examine the agreement between the color channels. Furthermore, when using calibration data to convert RGB film images to dose using the new method, poor correspondence between the dose calculations for the three color channels provides an important indication that the this new technique enables easy indication in case the dose and calibration films are curve mismatched. The method permit compensation for thickness nonuniformities in the film, increases the signal to noise level, mitigates the lateral dose-dependency of flatbed scanners effect of the calculated dose map and extends the evaluable dose range to 10 cGy-100 Gy. Multichannel dosimetry with radiochromic film like Gafchromic EBT2 is shown to have significant advantages over single channel dosimetry. It is recommended that the dosimetry protocols described be implemented when using this radiochromic film to ensure the best data integrity and dosimetric accuracy.
              Article 0 comments Cited 98 times – based on 0 reviews     Review now
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                Author and article information

                Journal
                Journal ID (nlm-ta): J Contemp Brachytherapy
                Journal ID (iso-abbrev): J Contemp Brachytherapy
                Journal ID (publisher-id): JCB
                Title: Journal of Contemporary Brachytherapy
                Publisher: Termedia Publishing House
                ISSN (Print): 1689-832X
                ISSN (Electronic): 2081-2841
                Publication date (Electronic): 30 April 2018
                Publication date (Print): April 2018
                Volume: 10
                Issue: 2
                Pages: 142-154
                Affiliations
                [1 ]Department of Radiotherapy Medical Physics, Northern Ireland Cancer Centre, Belfast City Hospital
                [2 ]Centre for Cancer Research and Cell Biology, Queen’s University, Belfast, Northern Ireland, United Kingdom
                Author notes
                Address for correspondence: Ahamed Badusha Mohamed Yoosuf, MSc, MIPEM, Department of Radiotherapy Medical Physics, Northern Ireland Cancer Centre, Belfast City Hospital, 51 Lisburn Road, Belfast BT9 7AB, United Kingdom. e-mail: ahamed.badusha@ 123456belfasttrust.hscni.net
                Article
                Publisher ID: 32737
                DOI: 10.5114/jcb.2018.75599
                PMC ID: 5961529
                SO-VID: 58f1fcd6-42be-4486-89e3-428783b7f1bd
                Copyright © Copyright: © 2018 Termedia Sp. z o. o.
                License:

                This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) License, allowing third parties to copy and redistribute the material in any medium or format and to remix, transform, and build upon the material, provided the original work is properly cited and states its license.

                History
                Date received : 14 November 2017
                Date accepted : 23 March 2018
                Categories
                Subject: Original Paper

                ScienceOpen disciplines: Oncology & Radiotherapy
                Keywords: liquid-filled ionization chamber,air vented ionization-chamber array,ebt3 film,multichannel dosimetry,local/global gamma analysis
                Data availability:
                ScienceOpen disciplines: Oncology & Radiotherapy
                Keywords: liquid-filled ionization chamber, air vented ionization-chamber array, ebt3 film, multichannel dosimetry, local/global gamma analysis

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