Implementation of a comprehensive set of optimised CBCT protocols and validation through imaging quality and dose audit.

OBJECTIVES: Cone-beam computed tomography (CBCT) for radiotherapy treatment verification has increased in frequency; therefore, it is crucial to optimise image quality and radiation dose to patients. The aim of this study was to implement optimised CBCT protocols for the Varian TrueBeams for most tumour sites in adult patients. METHODS: A combination of patient size-specific CBCT protocols from the literature and developed in-house was used. Scans taken before and after optimisation were compared by senior radiographers and physicists to evaluate how changes affected image quality and clinical usability for online image registration. The change in dose for each new CBCT protocol was compared to the Varian default. A clinical audit was performed following implementation to evaluate the changes in imaging dose for all patients receiving a CBCT during that period. RESULTS: Ten CBCT protocols were introduced including head and neck and patient-size-specific thorax and pelvis/abdomen protocols. Scans from 102 patients with images before and after optimisation were assessed, none of the scans showed image quality changes compromising clinical usability and for some image quality was improved. Between November 2020 and June 2021, 1185 patients had CBCTs using the new protocols. The imaging dose was reduced for 52% of patients, remained the same for 37% and increased for 12%. CONCLUSIONS: This study showed that substantial dose reductions and image quality improvements can be achieved with simple changes in the default settings of the Varian TrueBeam CBCT without affecting the radiographers' confidence in online image registration. ADVANCES IN KNOWLEDGE: This study represents a comprehensive assessment and optimisation of CBCT protocols for most sites, validated on a large cohort of patients.

Occupational radiation exposure in doctors: an analysis of exposure rates over 25 years.

OBJECTIVES: Healthcare professionals' occupational exposure to ionising radiation may be increasing due to increasing use of imaging and image-guided intervention. This study aims to assess the occupational exposure of doctors over a 25-year period at an NHS teaching hospital. METHODS: Dosemeter measurements were collected prospectively from 1995 to 2019. Two retrospective analyses were performed over time (first including all measurements, second excluding "zero-dose" measurements), and by speciality. Group comparisons were undertaken using multilevel linear regression; a p-value <0.05 was deemed significant. RESULTS: 8,892 measurements (3,983 body, 1,514 collar, 649 eye, 2,846 hand), of which 3,350 were non-zero measurements (1,541 body, 883 collar, 155 eye, 771 hand), were included. Whole dataset analysis found a significant decrease in exposure for radiologists and cardiologists, as measured by body, hand and collar dosemeters over the last 25 years (p < 0.01 for all). The non-zero readings reflect the whole cohort analysis except in the case of eye dosemeters, which showed a significant decrease in exposure for cardiologists (p < 0.01), but a significant increase for radiologists and surgeons/anaesthetists (p < 0.01 for both). CONCLUSIONS: Whilst ionising radiation remains an occupational risk for doctors, the overall decreasing trend in occupational exposure is reassuring. However, a significant rise in eye dose for radiologists, surgeons and anaesthetists is concerning, and close monitoring is required to prevent future issues. ADVANCES IN KNOWLEDGE: This paper is one of few evaluating the occupational radiation exposure to doctors over a 25-year period, showing that although most dosemeter measurements reflect decreasing exposure, the increase in eye exposure warrants caution.

IPEM Topical Report: An evidence and risk assessment based analysis of the efficacy of quality assurance tests on fluoroscopy units-part II; image quality.

This work aims to assess the efficacy of x-ray quality assurance tests undertaken on fluoroscopy units in the UK. Information was gathered on the results of image quality tests recommended by the reports of the Institute of Physics and Engineering in Medicine, and those additionally undertaken by medical physics departments. The assessment of efficacy considers the frequency with which a test result breaches the remedial level or other relevant threshold where applicable. The third quartile of those results exceeding the remedial level or threshold is used to estimate the severity of such a breach in terms of potential impact on patient dose and image quality. A risk assessment approach is then used to recommend to what degree, if any, the test should be included in an on-going test regimen. Data was analysed from 469 testing sessions to 337 unique fluoroscopy units throughout the UK. Across all tests, the rate with which the remedial level was exceeded varied from 0-10.6%, with severity ranging from little or none to major degradation to image quality or significant increase on population dose. Where possible, the data has also been used to produce representative ranges for the results of image quality tests. These could be useful as an up to date comparator for those sites considering the purchase of or commissioning new equipment. Overall the results indicate a wide range for the efficacy of those tests undertaken at present; this can be used to review local test protocols and to inform future changes to national guidance in the UK. The results also highlight some tests where measurement technique varies significantly throughout the UK, making any valid comparison difficult. This may indicate a need for further guidance on how best to undertake these tests.

IPEM Topical Report: an evidence and risk assessment based analysis of the efficacy of quality assurance tests on fluoroscopy units-part I; dosimetry and safety.

This work aims to assess the efficacy of x-ray quality assurance tests undertaken on fluoroscopy units in the UK. Information was gathered on the results of dosimetry and safety tests recommended by the reports of the Institute of Physics and Engineering in Medicine, and those additionally undertaken by medical physics departments. The assessment of efficacy considers the frequency with which a test result breaches the remedial level or other relevant threshold where applicable. The third quartile of those results exceeding the remedial level or threshold is used to estimate the severity of such a breach in terms of potential impact on patient dose and image quality. A risk assessment approach is then used to recommend to what degree, if any, the test should be included in an on-going test regimen. Data was analysed from 468 testing sessions to 336 unique fluoroscopy units throughout the UK. Across all tests, the rate with which the remedial level was exceeded varied from 0%-29.5%, with severity ranging from little or none to major degradation to image quality or significant increase on population dose. Where possible, the data has also been used to produce representative ranges for the results of dosimetric tests. These could be useful as an up to date comparator for those sites considering the purchase of or commissioning new equipment. Overall the results indicate a wide range for the efficacy of those tests undertaken at present; this can be used to review local test protocols and to inform future changes to national guidance in the UK. The results also highlight some tests where measurement technique varies significantly throughout the UK, making any valid comparison difficult. This may indicate a need for further guidance on how best to undertake these tests.

IPEM Topical Report: an evidence and risk assessment based analysis of the efficacy of tube and generator quality assurance tests on general x-ray units.

This work aims to assess the efficacy of current x-ray quality assurance (QA) testing regimes on tube and generator systems for general radiographic usage in the UK. 1393 sets of QA results data from nine UK medical physics departments were collected and analysed. Test failure rates ranged from 0% to 39% and were used to assess the likelihood of the test finding a fault. The magnitude of the recorded faults were used to assess the severity of the failure with due consideration to its impact on image quality and patient dose. The severity and likelihood of the faults were used along with a risk matrix to assess the efficacy of each test. Eleven tests were graded 'orange' (indicating an effective test that should be continued), four tests were graded 'yellow' (indicating a less effective test that may be continued with a lower frequency considered) and four tests were graded green (indicating a low efficacy test that could be removed from test regimes).

Is IORT ready for roll-out?

Two large randomised controlled trials of intraoperative radiotherapy (IORT) in breast-conserving surgery (TARGIT-A and ELIOT) have been published 14 years after their launch. Neither the TARGIT-A trial nor the ELIOT trial results have changed the current clinical practice for the use of IORT. The in-breast local recurrence rate (LRR) after IORT met the pre-specified non-inferiority margins in both trials and was 3.3% in TARGIT-A and 4.4% in the ELIOT trial. In both trials, the pre-specified estimates for local recurrence (LR) with external beam radiation therapy (EBRT) significantly overestimated actual LRR. In the TARGIT-A trial, LR with EBRT was estimated at the outset to be 6%, and in the ELIOT trial, it was estimated to be 3%. Surprisingly, LRR in the EBRT groups has been found to be significantly lower, 1.3% in the EBRT arm of the TARGIT-A and 0.4% in the EBRT arm of the ELIOT trial, respectively. Median follow-up was 2.4 years for the TARGIT-A trial and 5.8 years for the ELIOT trial. However, the initial cohort of patients in the TARGIT-A trial (reported in 2010) now have a median follow-up of 3.8 years and data on LR were available at 5 years follow-up on 35% of patients (18% who received IORT). Although further follow-up will increase confidence with the data, it will also further delay clinical implementation. By carefully weighing the risks and benefits of a single-fraction radiation treatment with patients, IORT should be offered within agreed and strict protocols. Patients deemed at low risk of LR or those deemed suitable for partial breast irradiation, according to the GEC-ESTRO and ASTRO recommendations, could be considered as candidates for IORT. These guidelines apply to all partial breast irradiation techniques, and more specific guidelines for IORT would assist clinicians.

Quality control within the multicentre perfusion CT study of primary colorectal cancer (PROSPeCT): results of an iodine density phantom study.

OBJECTIVES: To assess the cross-centre consistency of iodine enhancement, contrast-to-noise ratio and radiation dose in a multicentre perfusion CT trial of colorectal cancer. MATERIALS AND METHODS: A cylindrical water phantom containing different iodine inserts was examined on seven CT models in 13 hospitals. The relationship between CT number (Hounsfield units, HU) and iodine concentration (milligrams per millilitre) was established and contrast-to-noise ratios (CNRs) calculated. Radiation doses (CTDIvol, DLP) were compared across all sites. RESULTS: There was a linear relationship between CT number and iodine density. Iodine enhancement varied by a factor of at most 1.10, and image noise by at most 1.5 across the study sites. At an iodine concentration of 1 mg ml(-1) and 100 kV, CNRs ranged from 3.6 to 4.8 in the 220-mm phantom and from 1.4 to 1.9 in the 300-mm phantom. Doses varied by a factor of at most 2.4, but remained within study dose constraints. Iterative reconstruction algorithms did not alter iodine enhancement but resulted in reduced image noise by a factor of at most 2.2, allowing a potential dose decrease of at most 80% compared to filtered back projection (FBP). CONCLUSIONS: Quality control of CT performance across centres indicates that CNR values remain relatively consistent across all sites, giving acceptable image quality within the agreed dose constraints. KEY POINTS: Quality control is essential in a multicentre setting to enable CT quantification. CNRs in a body-sized phantom had the recommended value of at least 1.5. CTDIs and DLPs varied by factors of 1.8 and 2.4 respectively.

Effective DQE (eDQE) and speed of digital radiographic systems: an experimental methodology.

Prior studies on performance evaluation of digital radiographic systems have primarily focused on the assessment of the detector performance alone. However, the clinical performance of such systems is also substantially impacted by magnification, focal spot blur, the presence of scattered radiation, and the presence of an antiscatter grid. The purpose of this study is to evaluate an experimental methodology to assess the performance of a digital radiographic system, including those attributes, and to propose a new metric, effective detective quantum efficiency (eDQE), a candidate for defining the efficiency or speed of digital radiographic imaging systems. The study employed a geometric phantom simulating the attenuation and scatter properties of the adult human thorax and a representative indirect flat-panel-based clinical digital radiographic imaging system. The noise power spectrum (NPS) was derived from images of the phantom acquired at three exposure levels spanning the operating range of the clinical system. The modulation transfer function (MTF) was measured using an edge device positioned at the surface of the phantom, facing the x-ray source. Scatter measurements were made using a beam stop technique. The eDQE was then computed from these measurements, along with measures of phantom attenuation and x-ray flux. The MTF results showed notable impact from the focal spot blur, while the NPS depicted a large component of structured noise resulting from use of an antiscatter grid. The eDQE was found to be an order of magnitude lower than the conventional DQE. At 120 kVp, eDQE(0) was in the 8%-9% range, fivefold lower than DQE(0) at the same technique. The eDQE method yielded reproducible estimates of the system performance in a clinically relevant context by quantifying the inherent speed of the system, that is, the actual signal to noise ratio that would be measured under clinical operating conditions.

Artifacts found during quality assurance testing of computed radiography and digital radiography detectors.

A series of artifact images, obtained over 5 years of performance testing, of both computed radiography (CR) and integrated digital radiographic X-ray imaging detectors are presented. The images presented are all either flat field or test object images and show artifacts previously either undescribed in the existing literature or meriting further comment. The artifacts described are caused by incorrect flat field corrections, a failing amplifier, damaged detector lines affecting their neighbors, lost information between neighboring detector tiles, image retention, delamination of a detector, poor setup of mechanical movements in CR, suckers damaging a CR plate, inappropriate use of grid suppression software, inappropriate use of a low pass spatial frequency filter, and unsharp masking filters. The causes and significance of the artifacts are explained and categorized as software or hardware related. Actions taken to correct the artifacts are described and explained. This work will help physicists, radiographers, and radiologists identify various image quality problems and shows that quality assurance is useful in identifying artifacts.

Detector or system? Extending the concept of detective quantum efficiency to characterize the performance of digital radiographic imaging systems.

PURPOSE: To develop an experimental method for measuring the effective detective quantum efficiency (eDQE) of digital radiographic imaging systems and evaluate its use in select imaging systems. MATERIALS AND METHODS: A geometric phantom emulating the attenuation and scatter properties of the adult human thorax was employed to assess eight imaging systems in a total of nine configurations. The noise power spectrum (NPS) was derived from images of the phantom acquired at three exposure levels spanning the operating range of the system. The modulation transfer function (MTF) was measured by using an edge device positioned at the anterior surface of the phantom. Scatter measurements were made by using a beam-stop technique. All measurements, including those of phantom attenuation and estimates of x-ray flux, were used to compute the eDQE. RESULTS: The MTF results showed notable degradation owing to focal spot blur. Scatter fractions ranged between 11% and 56%, depending on the system. The eDQE(0) results ranged from 1%-17%, indicating a reduction of up to one order of magnitude and different rank ordering and performance among systems, compared with that implied in reported conventional detective quantum efficiency results from the same systems. CONCLUSION: The eDQE method was easy to implement, yielded reproducible results, and provided a meaningful reflection of system performance by quantifying image quality in a clinically relevant context. The difference in the magnitude of the measured eDQE and the ideal eDQE of 100% provides a great opportunity for improving the image quality of radiographic and mammographic systems while reducing patient dose.

Characterization of noise sources for two generations of computed radiography systems using powder and crystalline photostimulable phosphors.

The performances of two generations of computed radiography (CR) were tested and compared in terms of resolution and noise characteristics. The main aim was to characterize and quantify the noise sources in the images. The systems tested were (1) Agfa CR 25.0, a flying spot reader with powder phosphor image plates (MD 40.0); and (2) the Agfa DX-S, a line-scanning CR reader with needle crystal phosphor image plates (HD 5.0). For both systems, the standard metrics of presampled modulation transfer function (MTF), normalized noise power spectra (NNPS) and detective quantum efficiency (DQE) were measured using standard radiation quality RQA5 as defined by the International Electrotechnical Commission. The various noise sources contributing to the NNPS were separated by using knowledge of their relationship with air kerma, MTF, absorption efficiency and antialiasing filters. The DX-S MTF was superior compared with the CR 25.0. The maximum difference in MTF between the DX-S scan and CR 25.0 subscan directions was 0.13 at 1.3 mm(-1). For a nominal detector air kerma of 4 microGy, the peak DQE of the DX-S was 43 (+/-3)%, which was over double that of the CR 25.0 of 18 (+/-2)%. The additive electronic noise was negligible on the CR 25.0 but calculated to be constant 3.4 x 10(-7) (+/-0.4 x 10(-7)) mm2 at 3.9 microGy on the DX-S. The DX-S has improved image quality compared with a traditional flying spot reader. The separation of the noise sources indicates that the improvements in DQE of the DX-S are due not only to the higher quantum, efficiency and MTF, but also the lower structure, secondary quantum, and excess noise.