CT Quality Assurance Research Articles

Current status and guidelines for the assessment of tumour vascular support with dynamic contrast-enhanced computed tomography

Dynamic contrast-enhanced computed tomography (DCE-CT) assesses the vascular support of tumours through analysis of temporal changes in attenuation in blood vessels and tissues during a rapid series of images acquired with intravenous administration of iodinated contrast material. Commercial software for DCE-CT analysis allows pixel-by-pixel calculation of a range of validated physiological parameters and depiction as parametric maps. Clinical studies support the use of DCE-CT parameters as surrogates for physiological and molecular processes underlying tumour angiogenesis. DCE-CT has been used to provide biomarkers of drug action in early phase trials for the treatment of a range of cancers. DCE-CT can be appended to current imaging assessments of tumour response with the benefits of wide availability and low cost. This paper sets out guidelines for the use of DCE-CT in assessing tumour vascular support that were developed using a Delphi process. Recommendations encompass CT system requirements and quality assurance, radiation dosimetry, patient preparation, administration of contrast material, CT acquisition parameters, terminology and units, data processing and reporting. DCE-CT has reached technical maturity for use in therapeutic trials in oncology. The development of these consensus guidelines may promote broader application of DCE-CT for the evaluation of tumour vascularity. Key Points • DCE-CT can robustly assess tumour vascular support • DCE-CT has reached technical maturity for use in therapeutic trials in oncology • This paper presents consensus guidelines for using DCE-CT in assessing tumour vascularity.

SU-GG-I-73: CT Image Quality and Radiation Dose Survey in Taiwan

Introduction: The Standards for Medical Exposure Quality Assurance, derived from Ionizing Radiation Protection Act, was enforced in Taiwan since July 1, 2005. The first diagnostic facility, mammography, was included in the regulation since July 1, 2008. The Atomic Energy Council plans to include computed tomography(CT) in the next stage. Before that, the national survey for realizing the current level of CTquality assurance is necessary. The purpose of this study is to survey the image quality and patient doses for CT in Taiwan. Methods and Materials: Trained investigators conducted on‐site measurements, started from March 2009. An ACR CT accreditation phantom (Model 464, Gammex) was used to evaluate CTimage quality, including slice thickness accuracy, CT number accuracy, image uniformity, artifact, spatial resolution, and low contrast detectability. Computed tomography dose indexs(CTDI) in head and body phantoms were measured by a pencil‐type ionization chamber (10X6‐3CT, Radcal). Radiation beam width was assessed by chromic films (XR‐CT Dosimetry film, Gafchromic). Representative patient doses for adult head, adult abdomen, and 5‐years pediatric abdomen examinations were evaluated, including volume CTDI(CTDIvol). Results: There are 425 CT scanners, including CT, PET/CT, SPECT/CT, and CT simulator, in 241 hospitals in Taiwan. The preliminary results, obtained from March to December 2009, included 222 units in 142 hospitals. The fail rates of image quality items are low. The CTDIvol for adult head, adult abdomen, and 5‐years pediatric abdomen examinations are 58, 18, and 26 mGy. The rates of CTDIvol for adult head, adult abdomen, and 5‐years pediatric abdomen examinations over the ACR limits are 10%, 25%, and 32%. Conclusion: The preliminary results give us a view of current level in miniature of CTimage quality and patient doses in Taiwan. Once the survey is complete, final results will be useful and helpful references for the Atomic Energy Council.

CT quality assurance in the lung screening study component of the National Lung Screening Trial: implications for multicenter imaging trials.

The purpose of this study was to describe the effect of implementing an imaging quality assurance program on CT image quality in the Lung Screening Study component of the National Lung Screening Trial. The National Lung Screening Trial is a multicenter study in which 53,457 subjects at increased risk of lung cancer were randomized to undergo three annual chest CT or radiographic screenings for lung cancer to determine the relative effect of use of the two screening tests on lung cancer mortality. Of the 26,724 subjects randomized to the CT screening arm of the National Lung Screening Trial, the Lung Screening Study randomized 17,309 through 10 screening centers. The others were randomized through the American College of Radiology Imaging Network. Quality assurance procedures were implemented that included centralized review of a random sample of 1,504 Lung Screening Study CT examinations. Quality defect rates were tabulated. Quality defect rates ranged from 0% (section reconstruction interval) to 7.1% (reconstructed field of view), and most errors were sporadic. However, a recurrently high effective tube current-time product setting at one center, excessive streak artifact at one center, and excessive section thickness at one center were detected and corrected through the quality assurance process. Field-of-view and scan length errors were less frequent over the second half of the screening period (p < 0.01 for both parameters, two-tailed, paired Student's t test). Error rates varied among the screening centers and reviewers for most parameters evaluated. Our experience suggested that centralized monitoring of image quality is helpful for reducing quality defects in multicenter trials.

Iterative image reconstruction for CBCT using edge‐preserving prior

On-board cone-beam computed tomography (CBCT) is a new imaging technique for radiation therapy guidance, which provides volumetric information of a patient at treatment position. CBCT improves the setup accuracy and may be used for dose reconstruction. However, there is great concern that the repeated use of CBCT during a treatment course delivers too much of an extra dose to the patient. To reduce the CBCT dose, one needs to lower the total mAs of the x-ray tube current, which usually leads to reduced image quality. Our goal of this work is to develop an effective method that enables one to achieve a clinically acceptable CBCT image with as low as possible mAs without compromising quality. An iterative image reconstruction algorithm based on a penalized weighted least-squares (PWLS) principle was developed for this purpose. To preserve edges in the reconstructed images, we designed an anisotropic penalty term of a quadratic form. The algorithm was evaluated with a CT quality assurance phantom and an anthropomorphic head phantom. Compared with conventional isotropic penalty, the PWLS image reconstruction algorithm with anisotropic penalty shows better resolution preservation.

A study on adaptive IMRT treatment planning using kV cone-beam CT

Background and purpose Changes in tumor size during the course of radiotherapy warrant performing adaptive radiotherapy (ART). This work investigates the feasibility and usefulness of acquiring on-board cone-beam CT (CBCT) for ART for patients with bulky head and neck tumors treated with IMRT and for prostate patients with potentially significant target position variations during the treatment course. Materials and methods A phantom designed for CT quality assurance was used to compare the dosimetric and geometric accuracy between conventional CT and CBCT from a linear accelerator’s on-board imager. Patient planning CT and CBCT images were acquired before treatment and at mid-course. The IMRT plans made on the CT were applied to the CBCT and dose–volume histograms were calculated. Results In both phantom and patient studies, the dose–volume histograms (DVHs) based on CBCT images were in excellent agreement with DVHs based on planning CT images. Minimum, maximum and mean doses agreed very well. In a patient study, doses for targets and normal tissues from the same IMRT plans calculated on CBCT images agreed within 1–3% with those calculated on planning CT images. Conclusions CBCT images can be used to accurately predict dosimetric results. It is feasible to use CBCT to determine dosimetric consequences resulting from tumor shrinkage and patient geometry changes. An additional planning CT may be necessary to perform IMRT re-planning at present in order to accurately delineate tumor and organs. The CBCT has potential to become a very useful tool for on-line ART.

SU‐FF‐I‐55: A CT Daily Quality Assurance On‐Couch Procedure and Phantom in Radiation Oncology

Purpose: To design a simple yet comprehensive daily quality assurance (QA) program and phantom for CT Simulators in Radiation Oncology so that positioning laser and imaging QA can be performed on the flat couch using only one tool. This has been done to avoid removing the flat couch to perform CT QA and to simplify the daily QA procedure. Method and Materials: A new daily QA phantom was constructed by attaching to a commercially available CT QA phantom 3 adjustable legs and two metric scales in both vertical and horizontal directions. The two metric scales are used for laser QA, while the phantom body is used for CT imaging QA. Since the couch is scanned with the phantom, its effect on image quality was evaluated. The phantom is positioned on the couch such that couch effects are minimized. Four different GE CT scanners and 3 different Philips scanners were used to evaluate this phantom. Daily testing includes high and low contrast resolution, scale accuracy, CT number accuracy and uniformity. Results: The proposed program has been piloted in our institution. Inclusion of the couch produces different yet reproducible effects on image quality. The effects appear to be couch and scanner specific and are incorporated in the acceptability criteria for each CT scanner. Based on our data thus far, the presence of the couch does not change image resolution visually. It appears, however, that the couch causes changes in the uniformity of water's CT number. The effects are greatest in the section of the phantom closest to the couch. We thus limit our image quality evaluation to the central and 12 O'clock positions of the phantom. Conclusions: The proposed program and phantom has allowed us to implement a more comprehensive QA program while decreasing the level of effort by the simulation therapists.

TU‐E‐330D‐03: Evaluation of An OSL Dosimetry System for CT Quality Assurance and Dose Optimization

Purpose: Recent development of wide‐beam multidetector CT and conebeam CT demands alternative methodology to CTDI. In this study, the Optically Stimulated Luminescence (OSL) technique was evaluated for CT quality assurance and dose optimization. Method and Materials: CT scans were performed on 38‐mm2 thin Luxel™ dosimeters oriented in axial plane of a GE LightSpeed Ultra and at the center of a CT body dosimetry phantom. A 5‐mm beam collimation was selected to determine the energy response of the OSL detector at 80, 120, and 140 kVp stations. mA response of the OSL detector was evaluated from 60 to 350 mA. Helical scans of varying length coverage were also performed with the detector placed at the isocenter. The exposed OSL discs were measured using a Riso TL/OSL‐DA‐15 reader. Each OSL measurement was followed by a standard beta source irradiation and subsequent OSL measurement to normalize for the differing mass of the disks. The normalized OSL signal reading was used in the data analysis. Results: Good mA linearity was observed at all 3 kVp stations. There are discontinuities seen at ∼ 250 mA and it is known to be caused by tube focal spot change. The 120 and 140 kVp data show good correlation with ionization chamber reading. For 80 kVp, OSL signals to ion chamber readings are all higher, particularly at low mA range, indicating higher sensitivity of the OSL detector over the ion chamber. The helical scans show an increased OSL signal with scan length and a leveling of the signal at large scan coverage. Conclusion: The OSL detectors are of small size and responded well to CT exposure. It provides a practical technique for quantifying the dose at any location of a phantom for quality assurance and hence exhibits a potential for estimating patient organ dose.

It is time to retire the computed tomography dose index (CTDI) for CT quality assurance and dose optimization

It is time to retire the computed tomography dose index (CTDI) for CT quality assurance and dose optimization

It is time to retire the computed tomography dose index (CTDI) for CT quality assurance and dose optimization

Suggestions for topics suitable for these Point/Counterpoint debates should be addressed to Colin G. Orton, Professor Emeritus, Wayne State University, Detroit: ortonc@comcast.net. Persons participating in Point/Counterpoint discussions are selected for their knowledge and communicative skill. Their positions for or against a proposition may or may not reflect their personal opinions or the positions of their employers.

Is it time to retire the CTDI for CT quality assurance and dose optimization?

Is it time to retire the CTDI for CT quality assurance and dose optimization?

Grundlagen der Spiral-CT:: III. Qualitätssicherung

Since its introduction in 1989 spiral CT has gained wide clinical acceptance and meanwhile it covers a large range of CT applications. This new technology, however, has not yet been recognized and acknowledged in the national or international regulations on scanner quality assurance (QA) programs. The conventional QA procedures should be extended to check the distribution of resolution and noise within the image plane. Imaging performance in the axial direction constitutes one of the major advantages of spiral scanning. Therefore the slice sensitivity profiles and the spatial and low-contrast resolution along the z-axis have to be assessed. The high demands on table feed accuracy require additional tests.We suggest phantoms and procedures to check and quantify these parameters. Thereby we hope to support the ongoing discussion about spiral CT quality assurance.

Quality assurance in outpatient CT

Quality assurance in outpatient CT

Quality assurance in outpatient CT

Quality assurance in outpatient CT

CT quality assurance: Computer assisted slice thickness determination

The precise slice geometry of a CT scanner is an important, albeit tedious to determine, characteristic. A series of computer programs have been developed to analyze the slice thickness insert of the AAPM phantom. Without operator assistance they generate the beam profiles and slice thicknesses at three points in the scan field. A representative analysis is done on an AS&E scanner with slice thickness settings of 2 to 10 mm. The resulting discrepent measured thicknesses, ranging from 3 to 8 mm, indicate the need to perform such slice thickness measurements as part of a regular quality assurance program.