Single-Pass CT Chest/Abdomen/Pelvis for Oncology Patients: Effect on Radiation Dose and Image Quality Poster No.: C-1895 Congress: ECR 2015 Type: Scientific Exhibit Authors: 1 2 2 2 E. Lekgabe , N. Tran , W. Cheung , B. McDonald , H. 2 2 2 1 Kavnoudias , L. Hudson , X. Chen ; Melbourne, Victoria/AU, 2 Melbourne/AU Keywords: Dosimetric comparison, Diagnostic procedure, CT, Radioprotection / Radiation dose, Oncology DOI: 10.1594/ecr2015/C-1895 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 third- party 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. www.myESR.org Page 1 of 12 Aims and objectives CT plays a very important role in the imaging of oncology patients. However, the increasing use of CT in the last few decades has raised concerns regarding the risk of cancer from CT imaging. CT radiation dose is particularly important in oncology patients as they often require serial surveillance scans to monitor for the effectiveness of treatment, disease progression or recurrence. The aim of this study was to evaluate if patient CT radiation dose can be reduced without compromising image quality by using a single pass CT chest/abdomen/pelvis (CAP) imaging protocol when compared to the conventional imaging protocol, in oncology patients (1-4). Methods and materials Seventy oncology patients with previous conventional contrast enhanced (CE) CT CAP referred for restaging or surveillance CE CT CAP were imaged using the proposed protocol of two contrast injections and single-pass acquisition. The patients were all adult outpatients referred for restaging or surveillance scans. The conventional protocol at our institution is acquired in two segments (figure 1): • Chest: from above the lung apices to below the diaphragm. • Abdomen/pelvis: from above the diaphragm to ischial tuberosities. A single bolus of 80 ml of iodinated contrast (350ml/g) is used and administered at rate of 3ml/sec (figure 2). On the other hand, the research protocol was performed by dividing the volume of contrast into two boluses of 65 ml and 15 ml and administered separately. The 65 ml bolus was administered from 0 seconds (at a rate of 2.5 ml /sec) and the 15 ml bolus administered from 39 sec (rate: 2.5 ml/sec) (figure 2). Page 2 of 12 The CT CAP scan was then acquired in a single-pass acquisition at around 50 to 70 seconds. A sample of the images obtained from a research protocol scan is shown in figure 3. Auto bolus tracking software and automatic exposure control (AEC) were used in both scan protocols. All the scans, including the conventional protocol scans, were performed with the same scanner, GE LightSpeed VCT 64 slice (GE Healthcare, Milwaukee, WI, USA). The parameters measured include: 1. The dose-length-product (DLP) for the research and conventional protocol scans of each patient was recorded. 2. The image quality was retrospectively and individually evaluated by two experienced radiologists. The radiologists received a randomised list of the 140 scans, meaning each patient's two scans were not directly compared side by side. Each scan was given an image quality score using a 4-point scale, 1 represeting poor, 2 - moderate, 3 - good and 4 - excellent image quality. Inter- observer agreement (kappa) was calculated. The image quality scores for the two different scans were compared. 3. Radiographers performing the research protocol scans graded the ease of performing the scans, when compared to the conventional protocol, on a 5- point scale, 1 representing much easier, 3 not different and 5 much more difficult than the conventional protocol scan. 4. Attenuation values (Hounsfield units) of the aortic arch, pulmonary trunk, liver and spleen. The study was approved by the human research and ethics committee at our institution. Images for this section: Page 3 of 12 Page 4 of 12 Fig. 1: A scout view demonstrating the scan length for the conventional protocol scan. Overlap in the lower chest and upper abdomen accounts for the extra radiation reduced by a single-pass acquisition protocol. Fig. 2: Demonstration of contrast administration in the conventional CT CAP protocol and the research protocol. Page 5 of 12 Fig. 3: Selected images obtained from a scan performed using a single-pass acquisition CT CAP protocol. Note the dense contrast opacification of the abdominal aorta and its major branches, which is not normally seen with the conventional protocol. Page 6 of 12 Results 1. The average DLP for the research protocol was 669.70 mGy#cm and 923.01 mGy#cm for the conventional protocol, equating to average effective doses of 12.46 mSv and 17.17 mSv respectively, when using E/DLP conversion factor of 18.6 µSv/mGy cm(5) (Table 1). This corresponds to a radiation dose reduction of 27.44%. 2. The image quality scores are provided in table 2. There was poor Interobserver agreement between the two radiologists in regards to the individual scores, with low kappa values. However, when looking at the combined mean score for the two scans (abdomen and mediastinum) there was no significant difference, especially when considering that a score of 3 and above was regarded as good image quality. 3. In regards to the ease of the performing the research protocol scans by the radiographer, no research protocol scan was graded as a 4 or 5, meaning that they were not more difficult to perform than the conventional protocol scans. The majority were graded as scores of 1 or 2, and the remainder given scores of 3. 4. The mean attenuation values are shown in table 3. The values are significantly different in the mediastinum; however this did not seem to impact on the image quality grades assigned by the radiologists. The abdominal scores are not significantly different. However, whether the differences are statistically significant will depend on whether diagnostic accuracy is impacted. Diagnostic accuracy was not investigated in this study. None of the scans of the research protocol was required to be repeated due to poor image quality. There were no adverse events suffered by the patients undergoing research protocol scans during the study period. Images for this section: Page 7 of 12 Table 1: A table showing the average dose-length-product and effective dose results for the two scan protocols. Page 8 of 12 Table 2: Image quality assessment scores in the mediastinum and abdomen for the two scan protocols. Table 3: A table showing the results of the average attenuation values in the mediastinum and abdominal viscera (liver and spleen) for the two scan protocols. Page 9 of 12 Conclusion There was a significant (27%) patient radiation dose reduction for CT CAP in oncology patients by using a single-pass CT CAP protocol. The image quality of the single-pass protocol appears to be comparable to the conventional protocol. The single-pass protocol scans were also not more difficult to perform by radiographers than the conventional protocol scans. However, as stated below there were significant limitations encountered and more research in this area is required for validation of the results. Limitations: 1. Although the radiologists were not informed what protocol each scan was when grading the imaging quality, there is admittedly a slight visual difference between two scans. This is because in the research protocol scan, the aorta and its branches are opacified with denser contrast media (arterial phase contrast from the second bolus of contrast media). Therefore complete blinding was not achievable. 2. As stated above complete diagnostic accuracy was not assessed in this study. 3. Assessment of image quality is subjective, as was demonstrated by low kappa values. Personal information Ernest Lekgabe, MBBS Department of Radiology, The Alfred, Melbourne, Australia. Ngon Tran Head CT radiographer, Department of Radiology, The Alfred, Melbourne, Australia. Wa Cheung, MBBS, RANZCR Head of Body Imaging, Department of Radiology, The Alfred, Melbourne, Australia. Page 10 of 12