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Objective. Provide analyses of new organ dose coefficients (hereafter also referred to as normalized doses) for CT that have been developed to update the widely-utilized collection of data published 30 years ago in NRPB-SR250. Approach. In order to reflect changes in technology, and also ICRP recommendations concerning use of the computational phantoms adult male (AM) and adult female (AF), 102 series of new Monte Carlo simulations have been performed covering the range of operating conditions for 12 contemporary models of CT scanner from 4 manufacturers. Normalized doses (relative to free air on axis) have been determined for 39 organs, and for every 8 mm or 4.84 mm slab of AM and AF, respectively. Main results. Analyses of results confirm the significant influence (by up to a few tens of percent), on values of normalized organ (or contributions to effective dose (E 103,phan)), for whole body exposure arising from selection of tube voltage and beam shaping filter. Use of partial (when available) rather than a Full fan beam reduced both organ and effective dose by up to 7%. Normalized doses to AF were larger than corresponding figures for AM by up to 30% for organs and by 10% for E 103,phan. Additional simulations for whole body exposure have also demonstrated that: practical simplifications in the main modelling (point source, single slice thickness, neglect of patient couch and immobility of phantom arms) have sufficiently small (E 103,phan; mis-centring of the phantom away from the axis of rotation by 5 mm (in any direction) leads to changes in normalized organ dose and E 103,phan by up to 20% and 6%, respectively; and angular tube current modulation can result in reductions by up to 35% and E 103,phan, respectively, for 100% cosine variation. Significance. These analyses help advance understanding of the influence of operational scanner settings on organ dose coefficients for contemporary CT, in support of improved patient protection. The results will allow the future development of a new dose estimation tool.

Objective. Development of a method to provide organ and effective dose coefficients to reference adults for any CT scanner based on values of CTDI measured both in air and in standard CT dosimetry phantoms. Approach. Results from previous Monte Carlo simulations for a range of contemporary CT scanners have been analyzed to provide linear models relating values of organ dose (normalized to CTDI free-in-air), for each slab of 3 reference phantoms (ICRP Male/Female, and AH hermaphrodite), to similarly normalized values of CTDI in standard CT dosimetry phantoms. Three methods have been investigated to apply the models to values of CTDI for a ‘new’ scanner not previously simulated: a Generic approach using averaged normalized organ dose profiles for whole body exposure of the phantoms; and two processes for matching the scanner, on the basis of normalized organ doses or effective dose ( n E 103,phan ), to one of the 102 sets of dose coefficients previously calculated for 12 contemporary CT scanner models, from 4 manufacturers, operating under a range of conditions. Main results. The merit of each method has been quantitatively assessed when applied to both the present contemporary scanners with each test data set being excluded in turn during the matching process, and also to 3 previously-simulated older scanners. Whereas all three methods appear viable, with all doses being within 1% and 10% for the contemporary and old scanners respectively, matching to n E 103,phan is overall the approach preferred in practice, yielding an uncertainty of around 6% in estimated values of n E 103,phan . The present methodology also provides superior performance when compared against some other common normalization factors for E 103,phan . Significance. The CT dose model and the data sets will be incorporated into a new CT dosimetry tool that will be made available from UKHSA in support of facilitating improvements in patient protection.

Objective: To present the results following a UK national patient dose audit of paediatric CT examinations, to propose updated UK national diagnostic reference levels (DRLs) and to analyse current practice to see if any recommendations can be made to assist with optimisation. Methods: A UK national dose audit was undertaken in 2019 focussing on paediatric CT examinations of the head, chest, abdomen/pelvis and cervical spine using the methods proposed by the International Commission on Radiological Protection. The audit pro-forma contained mandatory fields, of which the post-examination dosimetry (volume CT dose index and dose–length product) and the patient weight (for body examinations) were the most important. Results: Analysis of the data submitted indicates that it is appropriate to propose national DRLs for CT head examinations in the 0-p). Conclusion: Updated UK national DRLs are proposed for paediatric CT examinations of the head and chest. Advances in knowledge: A national patient dose audit of paediatric CT examinations has led to the proposal of updated national DRLs.

We sought to compare objectively computed tomography (CT) scanner performance for three clinically relevant protocols using a task-based image quality assessment method in order to assess the potential for radiation dose reduction. Four CT scanners released between 2003 and 2007 by different manufacturers were compared with four CT scanners released between 2012 and 2014 by the same manufacturers using ideal linear model observers (MO): prewhitening (PW) MO and channelized Hotelling (CHO) MO with Laguerre-Gauss channels for high-contrast spatial resolution and low-contrast detectability (LCD) performance, respectively. High-contrast spatial resolution was assessed using a custom-made phantom that enabled the computation of the target transfer function (TTF) and noise power spectrum (NPS). Low-contrast detectability was assessed using a commercially available anthropomorphic abdominal phantom providing equivalent diameters of 24, 29.6, and 34.6 cm. Three protocols were reviewed: a head (trauma) and an abdominal (urinary stones) protocol were applied to assess high-contrast spatial resolution performance; and another abdominal (focal liver lesions) protocol was applied for LCD. The liver protocol was tested using fixed and modulated tube currents. The PW MO was proposed for assessing high-contrast detectability performance of the various CT scanners. Compared with older generation CT scanners, three newer systems displayed significant improvements in high-contrast detectability over that of their predecessors. A fourth, newer system had lower performance. The CHO MO was appropriate for assessing LCD performance and revealed that an excellent level of image quality could be obtained with newer scanners at significantly lower dose levels. This study shows that MO can objectively benchmark CT scanners using a task-based image quality method, thus helping to estimate the potential for further dose reductions offered by the latest systems. Such an approach may be useful for adequately and quantitatively comparing clinically relevant image quality among various scanners.

The aim of this study was to conduct a nationwide survey of computed tomography (CT) doses for a wide range of PET-CT and single photon emission computed tomography-computed tomography (SPECT-CT) imaging procedures, with the aim of generating proposed UK national diagnostic reference levels (NDRLs).CT protocol and dosimetry data for three PET-CT and seven SPECT-CT examinations were gathered from centres across the UK. Data were divided according to CT purpose (attenuation correction, localization or diagnostic) and third quartile values of scanner average dose metrics were used to generate suggested NDRLs for a range of examination and CT purpose combinations. Achievable doses were also established from the median of the dose distributions.Data were obtained from 47 centres, allowing suggested NDRLs to be produced for fluorine-18-fluorodeoxyglucose half-body PET-CT, and parathyroid, post-thyroid ablation, meta-iodobenzylguanidine/octreotide, cardiac and bone SPECT-CT examinations.Variations in dose of up to a factor of 35 were observed for a given examination/CT purpose combination. For fluorine-18-fluorodeoxyglucose half-body PET-CT examination dose levels for the three CT purposes overlapped, which highlights the variability in the way in which CT purposes are interpreted across the UK. This lack of standardization is believed to be the largest contributor to the dose variations that were observed. The survey highlighted the need for targeted optimization work in many centres.Suggested UK NDRLs and achievable doses for six common PET-CT and SPECT-CT examinations have been established as a result of this study.

This paper proposes a more inclusive statistical model for predicting image noise in Computed Tomography (CT), associated with scanning factors, considering the effect of beam hardening and image processing filters. It is based on power functions where the levels of the parameters will determine the rate of noise variation with respect to a given scanning factor. It includes the influence of tube potential, tube current, slice thickness, Field of View (FOV), reconstruction methods and post-processing filters. To validate the model, tomographic measurements were made by using a PMMA phantom that simulates paediatric head and adult abdomen, a PET bottle was used to simulate the head of the new-born. The influence of ROI (Region Of Interest) size over nonlinear model parameters was analysed, and high variations of powers of attenuation and FOV were found depending on ROI size. A nonlinear robust regression method was used. The validation was performed graphically by weighted residual analysis. A nonlinear noise model was obtained with an adjusted coefficient of determination for ROI sizes between 10% and 70% of the phantom diameter or FOV. The model confirms the significance of the tube current, slice thickness and beam hardening effect on image. The process of estimation of the parameters of the model by Nonlinear Robust Regression turned out to be optimal.

Some of the particular radiation safety challenges associated with PET/CT are described for those more familiar with working in conventional nuclear medicine departments. Facility design and shielding calculations are described and examples given. Challenges in keeping doses to the staff and public down are described with some of the approaches to keeping doses as low as reasonably achievable. Computed tomography (CT) technology and dose metrics are described in some detail, and some guidance on quality control checks and patient dose in CT and PET/CT is given with references to sources of information on these topics in this rapidly changing field.

Purpose The protocol for quality control of CBCT devices was produced as consensus among active MPEs of EFOMP, ESTRO and IAEA. It is available on-line since September 2017. In the beginning of 2018 we published an update including an appendix on patient dosimetry by EURADOS, comments by the German institute of standards (DIN) and remarks by users from countries that were not involved in the first edition, such as Austria, Costa Rica and Australia. This contribution gives a general overview of the guideline including insights about this recent update. Methods The guideline focuses on the measurement of objective image quality parameters and radiation output from any kind of CBCT device, including applications in dental radiology, C-arms and guidance systems in radiotherapy. Indications to use commercial or non-commercial phantoms and software are given, as well as to use ionization chambers or solid state dosemeters. The new EURADOS appendix includes an extensive review of patient dose data from recent research papers, organized by application and dose indicators: CTDI, DAP, effective dose, entrance surface dose, CTDIw, absorbed dose, D1-D2 and air kerma. The DIN has reviewed the details of the standards 6868–161 and 6868–15 for acceptance and constancy tests in dental CBCT. Individual comments have helped to clarify the measurements of radiation output and the methods to measure the modulation transfer function. Some colleagues have stressed the informative value of the appendices. Results The comments received were reviewed by the authors of the corresponding sections and discussed by the group in virtual meetings before being published as an update. The mentioned additions are meant to keep the document alive. They respond to questions raised by physicists that are starting to use the protocol inside and outside Europe. Conclusions The first presentation in the ECMP in Athens was followed by international presentations at ESTRO, ECR, IOMP and IRPA and national presentations in Italy, Spain, UK, Germany and other countries. Thanks to these voluntary efforts, physicists around the world are using and improving the document together. We also welcome your participation in this session and your feedback.

Evaluation of image quality (IQ) in Computed Tomography (CT) is important to ensure that diagnostic questions are correctly answered, whilst keeping radiation dose to the patient as low as is reasonably possible. The assessment of individual aspects of IQ is already a key component of routine quality control of medical x-ray devices. These values together with standard dose indicators can be used to give rise to 'figures of merit' (FOM) to characterise the dose efficiency of the CT scanners operating in certain modes. The demand for clinically relevant IQ characterisation has naturally increased with the development of CT technology (detectors efficiency, image reconstruction and processing), resulting in the adaptation and evolution of assessment methods. The purpose of this review is to present the spectrum of various methods that have been used to characterise image quality in CT: from objective measurements of physical parameters to clinically task-based approaches (i.e. model observer (MO) approach) including pure human observer approach. When combined together with a dose indicator, a generalised dose efficiency index can be explored in a framework of system and patient dose optimisation. We will focus on the IQ methodologies that are required for dealing with standard reconstruction, but also for iterative reconstruction algorithms. With this concept the previously used FOM will be presented with a proposal to update them in order to make them relevant and up to date with technological progress. The MO that objectively assesses IQ for clinically relevant tasks represents the most promising method in terms of radiologist sensitivity performance and therefore of most relevance in the clinical environment. publisher: Elsevier articletitle: Image quality in CT: From physical measurements to model observers journaltitle: Physica Medica articlelink: http://dx.doi.org/10.1016/j.ejmp.2015.08.007 content_type: article copyright: Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Associazione Italiana di Fisica in Medicina ispartof: Physica Medica vol:31 issue:8 pages:823-843 ispartof: location:Italy status: published

CT scans are an integral component of modern radiotherapy treatments, enabling the accurate localisation of the treatment target and organs-at-risk, and providing the tissue density information required for dose calculations in the treatment planning system. For these reasons, it is important to ensure exposures are optimised to give the required clinical image quality with doses that are as low as reasonably achievable. However, there is little guidance on dose levels in radiotherapy CT imaging either within the UK or internationally. This IPEM topical report presents the results of the first UK wide survey of dose indices in radiotherapy CT planning scans. Patient dose indices were collected for prostate, gynaecological, breast, 3D-lung, 4D-lung, brain and head/neck scans. Median values per scanner and examination type were calculated and national dose reference levels and 'achievable levels' of CT dose index (CTDIvol), dose-length-product (DLP) and scan length are proposed based on the third quartile and median values of these distributions, respectively. A total of 68 radiotherapy CT scanners were included in this audit. The proposed dose reference levels for CTDIvol and DLP are; prostate 16 mGy and 570 mGy.cm, gynaecological 16 mGy and 610 mGy.cm, breast 10 mGy and 390 mGy.cm, 3D-lung 14 mGy and 550 mGy.cm, 4D-lung 63 mGy and 1750 mGy.cm, brain 50 mGy and 1500 mGy.cm and head/neck 49 mGy and 2150 mGy.cm. Significant variations in dose indices were noted, with head/neck and 4D-lung yielding a factor of eighteen difference between the lowest and highest dose scanners. There was also evidence of some clustering in the data by scanner manufacturer, which may be indicative of a lack of local optimisation of individual systems to the clinical task. It is anticipated that providing this data to the UK and wider radiotherapy community will aid the optimisation of treatment planning CT scan protocols.

This is the second paper arising from a project concerning the application of Monte Carlo simulations to provide scanner-specific organ dose coefficients for modern CT scanners. The present focus is centred on the bone dosimetry models that have been developed. Simulations have been performed in photon only transport mode, with the assumption of electron equilibrium. This approximation breaks down for doses to active marrow and endosteum since the target cells are localised within tens of micrometre from bone tissue and dose enhancement functions are necessary to correct for the additional dose from photoelectric electrons created in adjacent material. The dose enhancement models used previously in publications NRPB-SR250 (Jones and Shrimpton 1993 Software Report NRPB-SR250, National Radiological Protection Board, Chilton, UK) and ORNL-TM8381 (Cristy and Eckerman 1987 Technical Report Oak Ridge National Laboratory, Oak Ridge, TN) have been implemented and compared with the contemporary approaches of Johnson et al (2011 Phys. Med. Biol. 56 2347-65) and ICRP Publication 116 (ICRP 2010 Ann. ICRP 40 1-257) that are being adopted in the present project. In addition, the calculation of dose to endosteum in the medullary cavity is reviewed and updated using electron mode simulations. For the purposes of quality assurance and comparison, the various dose enhancement functions have been applied in relation to the NRPB18+DJ and HPA18+ stylised hermaphrodite phantoms and also the adult male and female voxel phantoms recommended in ICRP Publication 110 (ICRP 2009 Ann. ICRP 39 1-165), for exposure from three CT scanners modelled previously. Contemporary results for standard examinations on the head and trunk calculated for these latter phantoms demonstrate moderate increases (modal value +18%) in active marrow dose coefficients relative to values derived from data published in NRPB-SR250. A similar analysis in relation to endosteum dose coefficients shows larger reductions (modal value -46%), owing at least in part to changes in assumed location of the target cells. Even larger changes are apparent for both of these dose coefficients in relation to examination of the upper legs (-39% and -94%, respectively). However, resultant changes in any values of effective dose will be less owing to the low weighting factors applied for these tissues.

Objective: To review doses to patients undergoing cervical spine CT examinations in the UK. Methods: A data collection form was developed and distributed to medical physicists and radiographers via e-mail distribution lists. The form requested details of CT scanners, exposure protocols and patient dose index information. Results: Data were received for 73 scanners. It was seen that 97% of scanners used automatic exposure control, and 60% of scanners used an iterative reconstruction technique for cervical spine examinations. The majority of scans were taken at 120 kV. The average patient dose indicators in terms of CT dose index (CTDIvol) ranged from 3.5 to 39.7 mGy (mean value 16.7 mGy), and for the DLP, ranged from 87 to 1030 mGy cm (mean value 379 mGy cm) as quoted for the standard 32 cm phantom. Conclusion: The rounded third quartile value of the mean dose distributions from this study were a CT dose index (CTDIvol) of 20 mGy and a dose–length product of 440 mGy cm as quoted for a 32 cm body phantom. These are significantly higher than those in the 2011 Public Health England CT dose survey when adjusted for phantom size. It is suggested that the existing national diagnostic reference levels for cervical spine CT should be amended, both with the new values and also to quote according to the 32 cm phantom. Advances in knowledge: Proposed new national diagnostic reference levels are presented for cervical spine CT examinations.

The CT scanner consists of many hardware and software features that affect patient dose. Many of these are controlled by the user, or are implicit within organ specific scan protocols. To understand many of these features and their implications on radiation dose to the patient, it is valuable to understand the CT dose indices that are commonly used and their limitations. This chapter begins by reviewing currently used, and accepted, dose descriptors for CT scanners, and outlines some of the limitations of these parameters whilst still advocating their valid use in the description of dose characteristics of CT scanners, and specifically in the comparison of CT scan protocols. The second part of the chapter discusses the effect of the scanner and scan protocol parameters on the dose to the patient. Specifically these are separated into some key hardware features, and then parameters which are usually selectable by the user within a scan protocol. A brief description and overview of these features are given, as well as aspects of their implications on image quality.