Cone beam CT based dose calculation in the thorax region

Kaplan, L.P.; Elstrøm, U.V.; Møller, D.S.; Hoffmann, Lone

doi:10.1016/j.phro.2018.09.001

Cited by 15 publications

(8 citation statements)

References 23 publications

(69 reference statements)

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“…The image quality of CT may have an impact on the calculated image. Although a recent study indicated that cone beam computed tomography (CBCT) images can be used for reference image calculation ( 18 , 28 , 29 ), the Monte Carlo method still requires high-precision image quality. Meanwhile, the CT dose and scan time should be considered in the QA protocol design.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of Daily CT for EPID-Based Transit In Vivo Dosimetry

Feng

et al. 2021

Front. Oncol.

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PurposeThe difference in anatomical structure and positioning between planning and treatment may lead to bias in electronic portal image device (EPID)-based in vivo dosimetry calculations. The purpose of this study was to use daily CT instead of planning CT as a reference for EPID-based in vivo dosimetry calculations and to analyze the necessity of using daily CT for EPID-based in vivo dosimetry calculations in terms of patient quality assurance.Materials and MethodsTwenty patients were enrolled in this study. The study design included eight different sites (the cervical, nasopharyngeal, and oral cavities, rectum, prostate, bladder, lung, and esophagus). All treatments were delivered with a CT-linac 506c (UIH, Shanghai) using 6 MV photon beams. This machine is equipped with diagnosis-level fan-beam CT and an amorphous silicon EPID XRD1642 (Varex Imaging Corporation, UT, USA). A Monte Carlo algorithm was developed to calculate the transmit EPID image. A pretreatment measurement was performed to assess system accuracy by delivering based on a homogeneous phantom (RW3 slab, PTW, Freiburg). During treatment, each patient underwent CT scanning before delivery either once or twice for a total of 268 fractions obtained daily CT images. Patients may have had a position correction that followed our image-guided radiation therapy (IGRT) procedure. Meanwhile, transmit EPID images were acquired for each field during delivery. After treatment, all patient CTs were reviewed to ensure that there was no large anatomical change between planning and treatment. The reference of transmit EPID images was calculated based on both planning and daily CTs, and the IGRT correction was corrected for the EPID calculation. The gamma passing rate (3 mm 3%, 2 mm 3%, and 2 mm 2%) was calculated and compared between the planning CT and daily CT. Mechanical errors [ ± 1 mm, ± 2 mm, ± 5 mm multileaf collimator (MLC) systematic shift and 3%, 5% monitor unit (MU) scaling] were also introduced in this study for comparing detectability between both types of CT.ResultThe average (standard deviation) gamma passing rate (3 mm 3%, 2 mm 3%, and 2 mm 2%) in the RW3 slab phantom was 99.6% ± 1.0%, 98.9% ± 2.1%, and 97.2% ± 3.9%. For patient measurement, the average (standard deviation) gamma passing rates were 87.8% ± 14.0%, 82.2% ± 16.9%, and 74.2% ± 18.9% for using planning CTs as reference and 93.6% ± 8.2%, 89.7% ± 11.0%, and 82.8% ± 14.7% for using daily CTs as reference. There were significant differences between the planning CT and daily CT results. All p-values (Mann–Whitney test) were less than 0.001. In terms of error simulation, nonparametric test shows that there were significant differences between practical daily results and error simulation results (p < 0.001). The receiver operating characteristic (ROC) analysis indicated that the detectability of mechanical delivery error using daily CT was better than that of planning CT. AUCDaily CT = 0.63–0.96 and AUCPlanning CT = 0.49–0.93 in MLC systematic shift and AUCDaily CT = 0.56–0.82 and AUCPlanning CT = 0.45–0.73 in MU scaling.ConclusionThis study shows the feasibility and effectiveness of using two-dimensional (2D) EPID portal image and daily CT-based in vivo dosimetry for intensity-modulated radiation therapy (IMRT) verification during treatment. The daily CT-based in vivo dosimetry has better sensitivity and specificity to identify the variation of IMRT in MLC-related and dose-related errors than planning CT-based.

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Section: Discussionmentioning

confidence: 99%

Evaluation of Daily CT for EPID-Based Transit In Vivo Dosimetry

Feng

et al. 2021

Front. Oncol.

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“…Several phantoms, briefly described in the supplementary material (Table S3), have been used to generate CBCT calibration curves. Errors up to 20.0% were calculated when using diagnostic CT scanners quality assurance phantoms [33,35,[49][50][51][52][53]. This can be attribute to the size of these phantoms (about 15 cm in diameter), which, due to the collimation used in standard CT scans, are of limited depth.…”

Section: Cbct Calibrationmentioning

confidence: 99%

A review of dose calculation approaches with cone beam CT in photon and proton therapy

2020

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Background and purpose: The use of cone beam computed tomography (CBCT) for performing dose calculations in radiation therapy has been widely investigated as it could provide a quantitative analysis of the dosimetric impact of changes in patients during the treatment. The aim of this review was to classify different techniques adopted to perform CBCT dose calculation and to report their dosimetric accuracy with respect to the metrics used. Methods and materials: A literature search was carried out in PubMed and ScienceDirect databases, based upon the following keywords: "cone beam computed tomography", "CBCT", "cone beam CT", "dose calculation", "accuracy". Sixty-nine peer-reviewed relevant articles were included in this review: thirty-one patient studies, fifteen phantom studies and twenty-three patient & phantom studies. Most studies were found to have focused on head and neck, lung and prostate cancers. Results: The techniques adopted to perform CBCT dose calculation have been grouped in six categories labelled as (1) pCT calibration, (2) CBCT calibration, (3) HU override, (4) Deformable image registration, (5) Dose deformation, and (6) Combined techniques. Differences between CBCT dose and reference dose were reported both for target volumes and OARs. Conclusions: A comparison among the available techniques for CBCT dose calculations is challenging as many variables are involved. Therefore, a set of reporting standards is recommended to enable meaningful comparisons among different studies. The accuracy of the results was strongly dependent on the image quality, regardless of the methods used, highlighting the need for dose validation and quality assurance standards. the results are highly variable due to different devices, protocols, datasets, metrics of comparison, treatment sites and treatment planning systems (TPS) being reported in the different studies. This wide variety in the dose reconstruction methodologies and reporting methods used in this expanding field has identified a need to review the current status of the field. This work considers the current

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“…In recent research projects, new methods were investigated to improve 4D-CBCT functionality in order to assess intra-fraction motion of moving targets and to suggest strategies for treatment adaptation [39] , [40] , [41] . Furthermore, accurate simulation of radiation dose contributions resulting from repeated CBCT examinations have been investigated in detail by several groups [42] , [43] , [44] , [45] .…”

Section: Cbct For Rt Position Verification and Adaptationmentioning

confidence: 99%