Contrast agents, Abdomen, CT, Contrast agent-intravenous, Cancer /ecr2015/C-1760

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1 Can Weight-Adapted IV Contrast Media Protocols Reduce Iodine Dose and Still Produce a Diagnostic Contrast Enhancement Level in Abdomino-Pelvic CT Scans? Poster No.: C-1760 Congress: ECR 2015 Type: Authors: Keywords: DOI: Scientific Exhibit E. Mott; London/UK Contrast agents, Abdomen, CT, Contrast agent-intravenous, Cancer /ecr2015/C-1760 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 10

2 Aims and objectives Computed Tomography (CT) is fundamental in the diagnosis and management of oncology patients. 1 With the use of CT increasing dramatically over the past decade, 2 it is imperative that CT scans are performed efficiently. The majority of CT abdomino-pelvic scans require intravenous contrast media containing iodine; this causes an increase in CT attenuation and enhances the visualisation of organs and vessels. 3 Currently, it is common practice to administer contrast media according to a fixed weight scale; 100ml (Omnipaque 350mgI/ml) is administered to patients weighing below 96kg; for patients weighing 96kg or above the dose is increased to 150ml. Administration utilising only two increments on the weight scale fails to consider patient habitus; which is reported as the most important patient factor affecting vascular and parenchymal contrast enhancement, due to the inverse relationship between contrast enhancement and patient habitus. 3 Consequently, an insufficient volume of contrast media may impact on the diagnostic information obtained from the CT image, while an excessive dose of iodine can lead to adverse effects such as contrast induced nephropathy (CIN). Whilst research has been undertaken, 4 there is no consensus on the most accurate method of adapting contrast media dose. Some researchers recommend adapting contrast dose based on total body weight (TBW). 5 Whereas, others state that lean body weight (LBW) is a more accurate measurement as it accounts for adipose tissue, which has small vascular and interstitial spaces and limits the dispersal of contrast in the blood. 6 Further research is needed to investigate weight-adapted contrast media doses and their validity in clinical practice. Therefore, the aim of this study was to trial a weight-adapted contrast media protocol for abdomino-pelvic CT imaging. This was achieved by: Reviewing published protocols on adaptive contrast media dose calculations Assessing contrast enhancement of the liver, portal vein, aorta and spleen using a weight-adapted contrast media protocol Exploring and discussing the practical and financial implications of a change in practice Methods and materials A quantitative non-inferiority study design was used to investigate if weight-adapted contrast media administration could yield similar diagnostic results compared to a fixed dose method of contrast media administration. Page 2 of 10

3 Thirty-nine oncology patients attending the CT department, for their routine follow-up CT scan, were selected using a convenience sampling method. To provide a paired historical control (control period), all patients had previously undergone CT abdomino-pelvic imaging at the institution using a fixed contrast media dose.during the interventional period, the same patients were prospectively imaged using a weight-adapted dose of 1.4ml/kg. A look-up table was developed for ease of use (Table 1). Departmental procedures were followed for all imaging acquisitions. There was no increase in ionising radiation as all scans were undertaken as part of routine follow-up requirements. Objective Assessment: To measure contrast enhancement levels (HU) in the liver, portal vein, aorta and spleen; regions of interest (ROI) were recorded from all CT images (figure 1). Subjective Assessment: Two Radiologists (one consultant, one experienced registrar) subjectively analysed overall contrast enhancement of all images using a 4-point scale. Statistical Analysis: Pearson's correlation coefficient (r) was used to analyse the relationship between HU and total body weight. The one sample, one-tailed t-test was used to compare the measured difference in contrast enhancement between protocols using a non-inferior margin of 10HU. Therefore, the adaptive protocol can be no worse than this specified margin to be judged as clinically acceptable. The Wilcoxon signed-rank was used to compare the subjective assessment ratings between protocols. Images for this section: Page 3 of 10

4 Table 1: Look-up table of contrast media dose required according to patient weight Page 4 of 10

5 Fig. 1: CT Image Demonstrating Region of Interest (ROI) Measurements Page 5 of 10

6 Results There were no substantial changes in patient weight between the control and intervention (mean weight 73.94kg and 73.42kg respectively); this indicated that the paired analysis has strength in comparing like with like. Figure 2 illustrates a negative correlation (r=-0.57, p=0.001) during the control period; this corresponds to an inverse correlation between contrast enhancement and patient weight and further supports previous research that a fixed contrast dose is not efficient in practice. 4 Figure 3 illustrates a decreased contrast enhancement variability between patients during the interventional period. However, the slight positive correlation (r=0.53, p=<0.001) may support previous research findings that adjusting contrast dose to TBW alone may overestimate the amount of contrast needed. 6 When contrast dose was adapted to patient weight, contrast enhancement levels were shown to be non-inferior to the current dose method (liver p<0.001; portal vein p= 0.003; aorta p=0.001; spleen p=0.001). These results allow the null hypothesis to be rejected and thus, support the research hypothesis that; by using a weight-adapted contrast administration protocol, contrast enhancement in abdomino-pelvic CT images is not inferior to contrast enhancement using the previous fixed dose method of contrast administration. As a group, patients received less contrast dose (overall reduction of ml) using the weight-adapted method. In addition, when using the weight-adapted protocol the mean cost per patient was reduced by 0.38; although a small amount, if applied to all patients attending the CT department this could reduce costs substantially. Furthermore, the subjective assessment showed no significant difference (p=0.068) between both protocols. All images acquired during the interventional period were rated as either good or excellent (table 2); similar results were shown for the control period, with the exception of one scan being graded adequate. Therefore, there may be scope to only use weight-based contrast when it reduces contrast dose to the patient. Images for this section: Page 6 of 10

7 Fig. 2: Scatterplot of weight against aortic HU during the control period Page 7 of 10

8 Fig. 3: Scatterplot of weight against aortic HU during the interventional period Table 2: Table illustrating the conbined results from the subjective assessment Page 8 of 10

9 Conclusion Improvements in clinical practice have been demonstrated in two ways: A contrast dose reduction for 64% of patients undergoing CT abdomino-pelvic imaging. A potential reduction in contrast media costs for the CT department. Therefore, if less contrast dose can be administered whilst still obtaining a similar diagnostic result, then a weight-adapted contrast media protocol should be implemented in clinical practice. However, for patients that would receive a higher dose than 100ml, further research is needed to evaluate the risks versus benefits of this increase in contrast media. Limitations A historical control was used; missing data and reliance on previous protocols being followed might have affected the results. To minimise these limitations in future, a monitored control period is recommended prior to any interventional period. The sample size for this study was smaller than some previous studies, 8 however, a sample size indicating 80% power was achieved. Personal information Emma Mott, BSc, MResCP. Senior Diagnostic Radiographer at Guy's and St Thomas' NHS Foundation Trust. emott@hotmail.co.uk This Study was completed as part of an MResCP Degree at St George's, University of London. References Page 9 of 10

10 (1) Great Britain. Department of Health. Managing high value capital equipment in the NHS in England. National audit office reported by the controller and audit general; 2011:3-5. (2) NHS England. NHS imaging and radiodiagnostic activity in England. Leeds: National Statistics; 2013 (3) Bae KT. Intravenous contrast medium administration and scan timing at CT: considerations and approaches. Radiology 2010;256(1):32. (4) Kondo H, Kanematsu M, Goshima S, Tomita Y, Miyoshi T, Hatcho A, et al. Abdominal multidetector CT in patients with varying body fat percentages: estimation of optimal contrast material dose. Radiology ;249(3): (5) Benbow M, Bull RK. Simple weight-based contrast dosing for standardization of portal phase CT liver enhancement. Clin Radiol ;66(10): (6) Ho LM, Nelson RC, Delong DM. Determining contrast medium dose and rate on basis of lean body weight: does this strategy improve patient-to-patient uniformity of hepatic enhancement during multi-detector row CT? Radiology 2007;243(2):431. (7) Nakaura T, Awai K, Maruyama N, Takata N, Yoshinaka I, Harada K, et al. Abdominal Dynamic CT in Patients with Renal Dysfunction: Contrast Agent Dose Reduction with Low Tube Voltage and High Tube Current-Time Product Settings at 256-Detector Row CT. Radiology ;261(2): (8)Yamashita Y, Komohara Y, Takahashi M, Uchida M,Hayabuchi N, Shimizu T, et al. Abdominal helical CT: evaluation of optimal doses of intravenous contrast material--a prospective randomized study. Radiology 2000;216(3):718. Page 10 of 10