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      Evaluation of a cone-beam computed tomography system calibrated for accurate radiotherapy dose calculation

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          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Graphical abstract

          Highlights

          • •

            A novel cone-beam computed tomography system was evaluated for dose calculation.

          • •

            Accurate calibration of the cone-beam computed tomography was possible.

          • •

            Dose calculation was within 1% of the prescribed dose for complex treatments.

          • •

            This allows for direct offline and on-line re-planning using cone-beam imaging.

          Abstract

          Background and purpose

          Dose calculation on cone-beam computed tomography (CBCT) images has been less accurate than on computed tomography (CT) images due to lower image quality and discrepancies in CT numbers for CBCT. As increasing interest arises in offline and online re-planning, dose calculation accuracy was evaluated for a novel CBCT imager integrated into a ring gantry treatment machine.

          Materials and methods

          The new CBCT system allowed fast image acquisition (5.9 s) by using new hardware, including a large-size flat panel detector, and incorporated image-processing algorithms with iterative reconstruction techniques, leading to accurate CT numbers allowing dose calculation. In this study, CBCT- and CT-based dose calculations were compared based on three anthropomorphic phantoms, after CBCT-to-mass-density calibration was performed. Six plans were created on the CT scans covering various target locations and complexities, followed by CBCT to CT registrations, copying of contours, and re-calculation of the plans on the CBCT scans. Dose-volume histogram metrics for target volumes and organs-at-risk (OARs) were evaluated, and global gamma analyses were performed.

          Results

          Target coverage differences were consistently below 1.2 %, demonstrating the agreement between CT and re-calculated CBCT dose distributions. Differences in D mean for OARs were below 0.5 Gy for all plans, except for three OARs, which were below 0.8 Gy (<1.1 %). All plans had a 3 %/1mm gamma pass rate > 97 %.

          Conclusions

          This study demonstrated comparable results between dose calculations performed on CBCT and CT acquisitions. The new CBCT system with enhanced image quality and CT number accuracy opens possibilities for off-line and on-line re-planning.

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          Most cited references45

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          Image-guided radiotherapy: from current concept to future perspectives.

          David Jaffray (2012)
          Radiotherapy is a highly effective, targeted therapy for the management of cancer. Technological innovations have enabled the direct integration of imaging technology into the radiation treatment device to increase the precision and accuracy of radiation delivery. As well as addressing a clinical need to better control the placement of the dose within the body, image-guided radiotherapy has enabled innovators in the field to accelerate their exploration of a number of different paradigms of radiation delivery, including toxicity reduction, dose escalation, hypofractionation, voxelization, and adaptation. Although these approaches are already innovative trends in radiation oncology, it is anticipated that they will work synergistically with other innovations in cancer management (including biomarker strategies, novel systemic and local therapies) as part of the broader goal of personalized cancer medicine. This Review discusses the rationale for adopting image-guidance approaches in radiotherapy, and the technology for achieving precision and accuracy in the context of different paradigms within the evolving radiation oncology practice. It also examines exciting advances in radiotherapy technology that suggest a convergence of radiotherapy practice in which patient-specific radiotherapy treatment courses are one of the most personalized forms of intervention in cancer medicine.
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            The calibration of CT Hounsfield units for radiotherapy treatment planning.

            E Pedroni, U Schneider, Michael Lomax (1995)
            Computer tomographic (CT) scans are used to correct for tissue inhomogeneities in radiotherapy treatment planning. In order to guarantee a precise treatment, it is important to obtain the relationship between CT Hounsfield units and electron densities (or proton stopping powers for proton radiotherapy), which is the basic input for radiotherapy planning systems which consider tissue heterogeneities. A method is described to determine improved CT calibrations for biological tissue (a stoichiometric calibration) based on measurements using tissue equivalent materials. The precision of this stoichiometric calibration and the more usual tissue substitute calibration is determined by a comparison of calculated proton radiographic images based on these calibrations and measured radiographs of a biological sample. It has been found that the stoichiometric calibration is more precise than the tissue substitute calibration.
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              Cone-beam computed tomography with a flat-panel imager: magnitude and effects of x-ray scatter.

              D. Jaffray, J Siewerdsen (2001)
              A system for cone-beam computed tomography (CBCT) based on a flat-panel imager (FPI) is used to examine the magnitude and effects of x-ray scatter in FPI-CBCT volume reconstructions. The system is being developed for application in image-guided therapies and has previously demonstrated spatial resolution and soft-tissue visibility comparable or superior to a conventional CT scanner under conditions of low x-ray scatter. For larger objects consistent with imaging of human anatomy (e.g., the pelvis) and for increased cone angle (i.e., larger volumetric reconstructions), however, the effects of x-ray scatter become significant. The magnitude of x-ray scatter with which the FPI-CBCT system must contend is quantified in terms of the scatter-to-primary energy fluence ratio (SPR) and scatter intensity profiles in the detector plane, each measured as a function of object size and cone angle. For large objects and cone angles (e.g., a pelvis imaged with a cone angle of 6 degrees), SPR in excess of 100% is observed. Associated with such levels of x-ray scatter are cup and streak artifacts as well as reduced accuracy in reconstruction values, quantified herein across a range of SPR consistent with the clinical setting. The effect of x-ray scatter on the contrast, noise, and contrast-to-noise ratio (CNR) in FPI-CBCT reconstructions was measured as a function of SPR and compared to predictions of a simple analytical model. The results quantify the degree to which elevated SPR degrades the CNR. For example, FPI-CBCT images of a breast-equivalent insert in water were degraded in CNR by nearly a factor of 2 for SPR ranging from approximately 2% to 120%. The analytical model for CNR provides a quantitative understanding of the relationship between CNR, dose, and spatial resolution and allows knowledgeable selection of the acquisition and reconstruction parameters that, for a given SPR, are required to restore the CNR to values achieved under conditions of low x-ray scatter. For example, for SPR = 100%, the CNR in FPI-CBCT images can be fully restored by: (1) increasing the dose by a factor of 4 (at full spatial resolution); (2) increasing dose and slice thickness by a factor of 2; or (3) increasing slice thickness by a factor of 4 (with no increase in dose). Other reconstruction parameters, such as transaxial resolution length and reconstruction filter, can be similarly adjusted to achieve CNR equal to that obtained in the scatter-free case.
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                Author and article information

                Contributors
                Didier Lustermans
                Journal
                Journal ID (nlm-ta): Phys Imaging Radiat Oncol
                Journal ID (iso-abbrev): Phys Imaging Radiat Oncol
                Title: Physics and Imaging in Radiation Oncology
                Publisher: Elsevier
                ISSN (Electronic): 2405-6316
                Publication date PMC-release: 29 February 2024
                Publication date Collection: January 2024
                Publication date (Electronic): 29 February 2024
                Volume: 29
                Electronic Location Identifier: 100566
                Affiliations
                Department of Radiation Oncology (Maastro), GROW School for Oncology and Reproduction, Maastricht University Medical Centre+, Maastricht, The Netherlands
                Author notes
                [* ]Corresponding author at: Postbox 3035, 6202 NA Maastricht, The Netherlands. didier.lustermans@ 123456maastrichtuniversity.nl
                [1]

                Both authors have contributed equally.

                Article
                Publisher Item ID: S2405-6316(24)00036-8 Publisher ID: 100566
                DOI: 10.1016/j.phro.2024.100566
                PMC ID: 10937948
                PubMed ID: 38487622
                SO-VID: f5a91fa7-1f77-4e42-a2fa-4770a910a88c
                Copyright © © 2024 The Authors
                License:

                This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

                History
                Date received : 3 November 2023
                Date revision received : 26 February 2024
                Date accepted : 27 February 2024
                Categories
                Subject: Original Research Article

                Keywords: radiotherapy,image quality,cone-beam computed tomography,dose calculation,ct number accuracy,metal artifact reduction
                Data availability:
                Keywords: radiotherapy, image quality, cone-beam computed tomography, dose calculation, ct number accuracy, metal artifact reduction

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