Dual Energy CT Cookbook - A Guide to Monoenergetic Plus Imaging in RT

Dual Energy CT cookbook A guide to Monoenergetic Plus imaging in RT siemens-healthineers.com/radiotherapy For SOMATOM CT users The scientific overlay is not that of the individual pictured and is not from a device of Siemens Healthineers. It was modified for better visualization. SIEMENS Healthineers Dual Energy CT cookbook · Foreword and Contributors Foreword Radiation Oncology is experiencing growth in This publication is a attempt to propagate this the use of Dual Energy imaging in treatment information for Siemens SOMATOM Dual Spiral planning. While it can seem daunting to start Dual Energy users. It presents a series of study integrating this technology in Radiation protocols and practical tips and tricks for several Therapy departments, the trend is inevitable body regions so that everyone can benefit from and has been embraced by physicists and Hospital del Mar’s experience. The information physicians alike. provided in this booklet can help support your entire clinical team in optimizing your workflow Hospital del Mar, Barcelona, Spain, together and providing the best imaging possible to with Siemens Healthineers, have investigated cancer patients undergoing radiation therapy. and developed optimal way of using Dual Energy CT for treatment planning. We are pleased to Finally, we look forward to hearing your share the knowledge and insights we gathered. feedback and suggestions, so that we at Siemens Healthineers can continually improve and partner with you in the care of your patients. Contributors Manuel Algara Enric Fernández-Velilla Nuria Rodríguez Ismael Membrive Javier Sanz Head of Radiation Oncology Medical Physicis Hospital Radiation Oncologist Radiation Oncologist Radiation Oncologist Department Hospital del Mar del Mar Hospital del Mar Hospital del Mar Hospital del Mar Universitat Autònoma Universitat Pompeu Fabra Universitat Pompeu Fabra 66 Anna Reig Palmira Foro Rafael Jimenez Carolina Lopez Radiation Oncologist Radiation Oncologist RT Supervisor RT Technologist Hospital del Mar Hospital del Mar Hospital del Mar Hospital del Mar Universitat Pompeu Fabra 2 Content · Dual Energy CT cookbook Content Evaluation methods Qualitative image assessment 4 Quantitative image assessment 5 Three key points to understand Dual Spiral Dual Energy for RT 1. What is Dual Energy? 6 2. What is Monoenergetic Plus? 6 3. What are the potential benefits in Radiation Oncology? 6 Head and neck imaging Motivation 7 Scan protocol 7 Tips and tricks 7 Iodine contrast tips and tricks in RT 9 Key takeaway 9 Brain imaging Motivation 10 Scan protocol 10 Tips and tricks 12 Key takeaway 12 Breast imaging Motivation 13 Scan protocol 13 Tips and tricks 13 Key takeaway 14 Prostate imaging Motivation 15 Scan protocol 15 Tips and tricks 15 Key takeaway 16 Results Optimum series for target delineation 17 Practical implementation of Dual Energy 17 Conclusion 18 Theory 19 References 22 3 Dual Energy CT cookbook · Evaluation methods Evaluation methods The goal of this evaluation was to establish the best keV level for the target delineation at the different clinical area, because Monoenergetic images can be generated with a range of 40–190 keV. Before going to the evaluation, four different keV levels were selected in the pre-study and the following evaluation was performed. Qualitative image assessment The different image series (Monoenergetic Plus 40 keV1, 45 keV1,2, 50 keV1, 55 keV1,2, and mix series (120 kV equivalent)) were assessed in a random order by four radiation oncologists with different levels of expertise (20, 10, 3, and 2 years in experience) in CT imaging for four different body regions: 1) Head and neck (8 cases), 2) Brain (10 cases), 3) Breast (10 cases), and 4) Prostate (7 cases) in order to evaluate qualitative image assessment. The reviewers were blinded to the applied reconstruction technique, but were aware that every case has cancer on the assessed image series. Images were displayed using the standard soft tissue window (window level 150; window width 600) as axial slices. Radiation oncologists were allowed and encouraged to alter the window settings at all available CT series if required in order to improve visualization. Qualitative image assessments were rated using a 5-point Likert scale (1 = not usable for target delineation, 2 = limited, 3 = moderate, 4 = good, 5 = excellent) for overall image quality, ease of target delineation (ranging from 1 = no delineation possible to 5 = clear border is provided for target delineation). Example Parameter 40 keV 45 keV 50 keV 55 keV 120 kV of the qualitative Overall image quality (1–5) results Target delineation (1–5) Image quality: 1 = not usable for target delineation, 2 = limited, 3 = moderate, 4 = good, 5 = excellent Target delineation: from 1 = no delineation possible to 5 = clear border is provided for target delineation 1 Optional 2 Requires syngo.via and syngo.CT DE Monoenergetic Plus 4 Evaluation methods · Dual Energy CT cookbook Quantitative image assessment Region of interests (ROI; size 12–36 mm2) were placed in a tumor and surrounding tissue (e.g., ipsilateral sternocleidomastoid muscle, brain tissue, iliopsoas muscle) to measure signal attenuation in mean Hounsfield units (HU). In cases where tumor necrosis was present, the ROI was placed in an peripheral vital tumor area. In general, ROIS were placed as large as possible, but with an adequate distance to surrounding anatomical structures and to avoid focal areas of heterogeneity. These measurements were performed three times and resulting values were averaged to ensure data consistency. The formula for calculating the tumor contrast-to-noise ratio (CNR) was as follows: CNR = (ROIT ROIS )/ SDS – (ROIT : average tumor enhancement, ROIS : attenuation of surrounding tissue, SDS : standard deviation of the surrounding tissue) All ROI measurements and calculated CNR were considered as quantitative image assessment parameters. Interobserver variability for target delineation was also evaluated by intersection (overlap of the ROIs) over the union, because union reflects the spread of volumes. The high value of this parameter indicates a variability among observers. Example Parameter 40 keV 45 keV 50 keV 55 keV 120 kV of the quantitative Interobserver variability results (intersection / union; %) Tumor enhancement (HU) Surrounding tissue attenuation (HU) CNR 5 Dual Energy CT cookbook · Three key points Three key points to understand Dual Spiral Dual Energy[1] for RT 1. What is Dual Energy? Unlike a standard 120 kV scan, Dual Energy (DE) CT requires two spiral scans acquired at 80 kV and 140 kV (Dual Spiral DE). The two scans at two different energies provide images with different HU values, varying by the tissue type [1]. This information is then used to generate Monoenergetic Plus [2],[3] image by projecting the measured HU values of the low and the high kV scan. Radiation dose in DE scans is equal to single energy acquisition. 2. What is Monoenergetic Plus [3]? Monoenergetic Plus is an application that simulates what the actual image HU would look like if the study was acquired with a monochromatic X-ray beam 40 keV at that energy in a range of 40–190 keV. The following steps are automatically performed in order to create the result: soft . . ......... 1) fully automated Dual Energy acquisition, 2) non-rigid registration is I tissue performed to ensure the exact matching of both kV images, 3) the results are fat automatically reconstructed based on user’s preference. keV 3. What are the potential benefits in Radiation Oncology? • Fewer beam-hardening artifacts due to virtual monochromatic spectrum ............ • Monoenergetic Plus lets users easily compare and quantify lesions and tissues. This means: Target delineation improvement[4] - Target margin reduction [4] - Potentially less target delineation variability - 6 Head and neck imaging · Dual Energy CT cookbook Head and neck imaging Motivation One challenge of CT head and neck imaging compared with MRI is the lower soft tissue contrast, which makes it difficult to differentiate lymph nodes, tumor, and blood vessels for target delineation. CT Dual Energy Monoenergetic Plus has the potential to improve target delineation and higher CNR. In order to validate this hypothesis, qualitative and quantitative assessments were performed. Scan protocol Scan protocol Scan parameters Reconstruction Important remarks parameters Topogram • Craniocaudal position Neck RT 120 kV Slice thickness: • Optimized kV CTDI: 18.17 mGy 1.5 / 1.2 mm with DirectDensity™,1 Reconstruction kernel: if available B30 / Br38 • Used for dose calculation Contrast Delay 100 s • Total amount: 110 ml (300 mgI iodine) • Injection rate: 2-2.5 ml / second (variable amount based on body weight may be considered) Dual Energy 1) 80 kV Slice thickness: • Iterative reconstruction Head and neck Pitch: 0.6 1.5 / 1.2 mm such as SAFIRE2 may CTDI: 8.57 mGy Reconstruction kernel: be used 2) 140 kV D30 / Qr36 • Body part: Head & Neck Pitch: 0.8–1.2 (it may vary by scanner type) Auto post processing: • iMAR2 should be applied CTDI: 9.88 mGy DE_Mono_40 keV when metal artifacts are observed (e.g., dental implant) Tips and tricks • Standard Dual Energy protocol3 is used in order to create RT Head and neck protocol. Adjustments of CTDI, slice thickness, and reconstruction kernel as well as auto postprocessing results are required before saving as RT protocol. • To ensure the exact matching of both kV images, non-rigid registration is performed automatically prior to generating Monoenergetic Plus images. • Delay time should be at least 75 seconds, because contrast is plateauing during Dual Energy acquisition. 1 Optional; DirectDensity™ reconstruction is designed for use in Radiation Therapy Planning (RTP) only. DirectDensity™ reconstruction is not intended to be used for diagnostic imaging. 2 Optional 3 Protocol: DE_Abdomen_LiverVNC_late 7 Dual Energy CT cookbook · Head and neck imaging Qualitative Parameter 40 keV 45 keV 50 keV 55 keV 120 kV image assessment Overall image quality (1–5) 4.1 3.7 4.0 3.3 3.0 Target delineation (1–5) 4.0 3.7 3.6 3.6 3.0 Quantitative Parameter 40 keV 45 keV 50 keV 55 keV 120 kV image assessment Interobserver variability (%) 36.9 30.8 27.9 31.6 31.6 Tumor enhancement (HU) 230.7 193.4 163.1 139.8 92.8 Noise (HU) 16.0 13.9 12.0 10.6 8.7 Soft tissue attenuation (HU) 99.0 89.7 82.5 77.0 66.4 CNR 8.9 8.0 7.2 6.3 3.2 1 Figure 1: left: 120 kV right: Monoenergetic Plus 40 keV Overall image quality is rated highest at 40 keV. 2 Figure 2: left: 120 kV right: Monoenergetic Plus 40 keV Interobserver variability is rated the best at 40 keV, improved from 3.16 (120 kV) to 2.71 (40 keV); this means less variability. 3 Figure 3: left: 120 kV right: Monoenergetic Plus 40 keV Overall, tumor visualization is considerably improved at 40 keV. 8 Head and neck imaging · Dual Energy CT cookbook Iodine contrast tips and tricks in RT One of the inherent issues of computed tomography (CT) versus magnetic resonance imaging (MRI) is the soft tissue contrast. Use of iodine contrast allows enhanced visualization of target volumes and adjacent organs at risk; making delineation of radiotherapy target volumes and organs at risk potentially easier, particularly for head and neck imaging. Here is the summary of how the iodine contrast is used when applying Dual Spiral Dual Energy for RT. (The theory is applicable for all clinical areas.) Density (HU) Arterial phase Venous phase Delayed phase tissue density curve vein density curve artery density curve Time after the injection -> (75–180 s) Dual Spiral Dual Energy With 80 kV/ 140 kV • When using Dual Spiral Dual Energy with iodine contrast, keep in mind that delay time is set to at least 75 seconds (delayed phase) where the time density curve is close to flat, so that two consecutive scans at 80 kV and 140 kV have almost the same amount of iodine contrast information. • Intravenous cannula is required prior to imaging Key takeaway • Based on the assessment, 40 keV was found to be the optimum keV level for target delineation, because it showed significant improvement for 1) overall image quality, 2) target delineation, 3) CNR, and 4) interobserver variability. • Two acquisitions are needed for head and neck imaging: 1) 120 kV acquisition without iodine contrast for dose calculation and 2) Dual Energy acquisition with the iodine contrast used for target delineation. Therefore, non-contrast image is matched with Monoenergetic Plus 40 keV in the TPS. 9 Dual Energy CT cookbook · Brain imaging Brain imaging Motivation The current utilization of CT in brain tumor typically involves alignment with MRI scans. MRI provide the soft tissue contrast necessary for tumor identification and improved structure delineation, while CT images support convenient generation of the electron density maps necessary for dose calculation. However, due to the fact that 1) MRI is not always applicable due to its availability and 2) patients may have a contraindication for MRI, CT still plays a very important role to address the target delineation. Scan protocol Scan protocol Scan parameters Reconstruction Important remarks parameters Topogram • Craniocaudal position Brain RT 120 kV Slice thickness: • Optimized kV 1.5 / 1.2 mm with DirectDensity™,1 Reconstruction kernel: if available B30 / Br38 • Used for dose calculation Contrast Delay 180 s • Total amount: 80 ml • Injection rate: 3 ml / s Dual Energy Brain 1) 80 kV Slice thickness: • Iterative reconstruction Pitch: 0.6 1.5 / 1.2 mm such as SAFIRE2 may CTDI: 8.57 mGy Reconstruction kernel: be used 2) 140 kV D30 / Qr36 • Body part: Head Pitch: 0.8–1.2 (it may vary by scanner type) Auto post processing: • iMAR2 should be CTDI: 9.88 mGy DE_Mono_40 keV applied when metal artifacts are observed (e.g., dental implant) 1 Optional; DirectDensity™ reconstruction is designed for use in Radiation Therapy Planning (RTP) only. DirectDensity™ reconstruction is not intended to be used for diagnostic imaging. 2 Optional 10 Brain imaging · Dual Energy CT cookbook Qualitative Parameter 40 keV 45 keV 50 keV 55 keV 120 kV image Overall image quality (1–5) assessment 4.0 3.7 3.5 3.5 3.5 Target delineation (1–5) 3.6 3.7 3.6 3.6 3.4 Quantitative Parameter 40 keV 45 keV 50 keV 55 keV 120 kV image Interobserver variability (%) 38.5 28.6 34.5 37.0 34.5 assessment Tumor enhancement (HU) 115.6 98.3 83.5 74.1 53.6 Noise (HU) 21.0 17.5 12.6 11.1 12.0 Soft tissue attenuation (HU) 86.1 78.6 72.1 68.5 59.8 CNR 2.3 2.2 2.2 1.9 1.6 4 Figure 4: left: 120 kV right: Monoenergetic Plus 40 keV A lot of guesswork needed at 120 kV, while the border of the tumor is clearly shown at 40 keV. 5 V. Figure 5: left: 120 kV right: Monoenergetic Plus 40 keV Clear soft tissue contrast is demonstrated for brain metastasis at 40 keV. 6 Figure 6: left: 120 kV right: Monoenergetic Plus 40 keV Overall, tumor visualization is markedly improved at 40 keV. 11 Dual Energy CT cookbook · Brain imaging Tips and tricks • Standard Dual Energy protocol1 should be used in order to create RT Head protocol. Adjustments of CTDI, slice thickness, body part (to Head), and reconstruction kernel as well as auto postprocessing results are required in order to optimize the RT Brain protocol. • Two acquisitions are needed for brain imaging: 1) 120 kV acquisition without iodine contrast for dose calculation and 2) Dual Energy acquisition with the iodine contrast used for target delineation. Therefore, non-contrast image is matched with Monoenergetic Plus 40 keV in the TPS. • When using iodine contrast with Dual Spiral Dual Energy, delay time should be set to at least 75 seconds (delayed phase) where the time density curve is close to flat, so that two consecutive scans at 80 kV and 140 kV have almost the same amount of iodine contrast information. Key takeaway • Based on the analysis, 40 keV was found to be the optimum keV level for target delineation in terms of overall image quality, interobserver variability, soft tissue attenuation, and CNR. However, there was no remarkable difference between 40–55 keV, probably because of its higher noise level and intermediate CNR improvement, although 120 kV was found to be the most difficult for target delineation. • Interobserver variability seemed to be improved slightly with lower keV levels. (More samples are needed to be statistically significant.) • In cases with patients who have not undergone surgery, Dual Energy shows the best results due to higher contrast of the tumor. • Postoperative cases provide visualizations that allow discrimination of parenchyma from surgical cavity with Dual Energy Monoenergetic Plus 40 keV. 1 Protocol: DE_Head_BrainHem_post_intervention 12 Breast imaging · Dual Energy CT cookbook Breast imaging Motivation Elective radiation therapy of early-stage breast cancer has proved to be very effective in lowering the risk of recurrences and improving overall survival, and it is therefore offered to many patients in the postoperative setting. However, there is also treatment-related morbidity in breast, heart disease, and secondary cancer development[5]. The risk of local recurrence has progressively decreased over the last decades [6], while overall survival of breast cancer patients improved considerably [7]. It is therefore increasingly important to provide optimal target delineation for the patients to obtain a maximal effect at the lowest risk of late morbidity [8]. Within this study, Dual Energy acquisition was performed for postoperative patients, and targets are delineated in order to perform the dose escalation. Scan protocol Scan protocol Scan parameters Reconstruction Important remarks parameters Topogram • Craniocaudal position • Supine position Dual Energy 1) 80 kV Slice thickness: • Iterative reconstruction Breast Pitch: 0.6 1.5 / 1.2 mm such as SAFIRE2 may be CTDI: 8.57 mGy Reconstruction kernel: used 2) 140 kV B30 / Qr36 • Body part: Breast Pitch: 0.8–1.2 (it may vary by scanner type) 1) Dose calculation • iMAR2 should be applied CTDI: 9.88 mGy a) mixed 120 kV when metal artifacts are B30 / Q36 2 mm observed (e.g., pace (for dose calculation) maker) b) DirectDensity™,1 at 140 kV 2) Target delineation Auto post processing: DE_Mono_40 keV (for target delineation) Tips and tricks • Standard Dual Energy protocol3 is used in order to create RT Breast protocol. Adjustments of CTDI, slice thickness, and reconstruction kernel as well as auto postprocessing results are required before saving as RT protocol. • Since breast imaging with Dual Energy offers sufficient soft tissue contrast (tumor and fat), iodine contrast was not used in the examination. 1 Optional; DirectDensity™ reconstruction is designed for use in Radiation Therapy Planning (RTP) only. DirectDensity™ reconstruction is not intended to be used for diagnostic imaging. 2 Optional 3 Protocol: DE_Abdomen_LiverVNC_late 13 Dual Energy CT cookbook · Breast imaging Qualitative Parameter 40 keV 45 keV 50 keV 55 keV 120 kV image Overall image quality (1–5) assessment 3.7 3.7 4.0 4.1 3.9 Target delineation (1–5) 4.0 4.0 4.0 3.9 4.0 Quantitative Parameter 40 keV 45 keV 50 keV 55 keV 120 kV image Tumor enhancement (HU) 24.6 20.9 18.1 16.2 11.3 assessment Fat tissue attenuation (HU) -180.4 -162.2 -148.0 -137.6 -114.1 Noise (HU) 22.8 20.5 18.9 17.4 16.3 CNR 9.0 8.9 8.8 8.8 7.7 7 Shoving wist 5 findings 8 ............. -150 Energy Nevi 300: 110 120 130 140 150 160 170 180 190 Figure 7: Figure 8: Monoenergetic graph shows how the HU value left: 120 kV-equivalent image (y-axis) changes when different keV (x-axis) is right: Monoenergetic Plus 40 keV selected. It shows better soft tissue contrast at lower keV because the HU value of the fat (orange Tumor visualization is improved at 40 keV although line) decreases, whereas HU of tumor (white line) sufficient contrast is available at 120 kV-equivalent image. increases. Key takeaway • All series rated good overall image quality and target delineation (incl. 120 kV). • No remarkable differences are observed among the series. This could probably be caused by sufficient CNR at 120 kV even without using Dual Energy due to sufficient contrast between fat and tumor. • This study focused on patients who received radiation therapy after surgery. Target delineation of the tumor was done for dose escalation purposes. Further investigation is needed to evaluate lymphatic areas (axillary / supraclavicular/ internal mammary chain), because those have less soft tissue contrast. 14 Prostate imaging · Dual Energy CT cookbook Prostate imaging Motivation The current practice in prostate radiotherapy is for the treatment volume to encompass the entire prostate gland and a variable portion of the seminal vesicles. The intended treatment volumes need to be properly defined so that the radiotherapy beams can be accurately focused on the target volume and avoid a geographic miss that would reduce local tumor control. There are limitations to the accuracy of CT-defined radiotherapy volumes, owing to difficulties in the visualization of the soft tissue boundaries between the prostate gland and its surrounding pelvic organs, especially in the determination of the apex of the prostate gland. The use of CT Dual Energy Monoenergetic Plus has potential to improve the target delineation by higher CNR. Within this study, the prostate was delineated as target to evaluate the benefit of Monoenergetic Plus. Scan protocol Scan protocol Scan parameters Reconstruction Important remarks parameters Topogram • Craniocaudal position Dual Energy 1) 80 kV Slice thickness: • Iterative reconstruction Prostate Pitch: 0.6 1.5 / 1.2 mm such as SAFIRE2 may be CTDI: 8.57 mGy Reconstruction kernel: used 2) 140 kV B30 / Qr36 • Body part: Prostate Pitch: 0.8–1.2 (it may vary by scanner type) 1) Dose calculation • iMAR2 should be applied CTDI: 9.88 mGy a) mixed 120 kV when metal artifacts B30 / Q36 2 mm are observed (for dose calculation) (e.g., Hip implant) b) DirectDensity™,1 at 140 kV 2) Target delineation Auto post processing: DE_Mono_40 keV (for target delineation) Tips and tricks • Standard Dual Energy protocol3 is used in order to create RT Prostate protocol. Adjustments of CTDI, slice thickness, and reconstruction kernel as well as auto postprocessing result are required before saving as RT Prostate DE Protocol. • To ensure the exact matching of both kV images, non-rigid registration is automatically performed when Monoenergetic Plus image is generated. 1 Optional; DirectDensity™ reconstruction is designed for use in Radiation Therapy Planning (RTP) only. DirectDensity™ reconstruction is not intended to be used for diagnostic imaging. 2 Optional 3 Protocol: DE_Abdomen_LiverVNC_late 15 Dual Energy CT cookbook · Prostate imaging Qualitative Parameter 40 keV 45 keV 50 keV 55 keV 120 kV image Overall image quality (1–5) assessment 4.1 3.7 4.0 3.3 3.0 Target delineation (1–5) 4.0 3.7 3.6 3.6 3.6 Quantitative Parameter 40 keV 45 keV 50 keV 55 keV 120 kV image Interobserver variability (%) 47.6 47.6 50.0 assessment 41.7 43.5 Prostate attenuation (HU) 52.2 49.1 47.3 45.2 41.4 Fat tissue attenuation (HU) -152.6 -133.2 -119.4 -107.5 -81.1 Noise (HU) 22.1 20.3 18.0 16.4 13.6 CNR 9.2 9.0 9.2 9.2 9.0 9 Figure 9: left: 120 kV-equivalent image right: Monoenergetic Plus 40 keV Monoenergetic Plus slightly increases the HU value on the prostate. Key takeaway • Based on the analysis, 40 keV was found to be the optimum keV level for prostate imaging for target delineation because it showed 1) good overall image quality, and 2) best score for target delineation. • There was almost no CNR change between different series; however, CNR depends on which organs are considered as comparison (with this study, fat was used), because prostate has many surrounding organs (e.g., fat, seminal vesicles, rectum, bladder, etc.). Therefore, further investigation might be needed in order to identify the optimum series. • Further investigation is needed to differentiate bladder and prostate by using iodine contrast. Dual Energy may potentially benefit by enhancing the iodine for target delineation. 16 Results · Dual Energy CT cookbook Results Optimum series for target delineation Target delineation Best series for Comments target delineation Head and neck 40 keV 40 keV shows the best result for all criteria. (with contrast medium) Brain 40 keV 40 keV shows the best result for non-operative (with contrast medium) patients, while postoperative cases show intermediate improvement for outline of the cavity. Breast 40 keV or 120 kV When target delineation is performed for (single energy) boosting purpose, 120 kV might be sufficient because adequate contrast between tumor and surrounding tissue (fat) is available even with 120 kV. In cases with delineating lymphatic areas with iodine contrast, 40 keV is probably beneficial. (Further investigation is needed.) Prostate 40 keV Study shows intermediate improvement at 40 keV compared with 120 kV. Using iodine contrast to differentiate prostate and bladder is potentially improved further by using Dual Energy. Moving organs such as liver, kidney, and pancreas were not considered due to the limitation of two consecutive acquisitions (temporal coherence).To address these organs, TwinBeam Dual Energy1 is recommended by enabling simultaneous acquisition for moving organs. Practical implementation of Dual Energy Perspective Consideration Therapist Acquisition and postprocessing is as easy as when you’re doing a single energy scan. Physicist No changes in the workflow. Dosimetrist No changes in the workflow because only Monoenergetic Plus images are sent directly to the TPS, thanks to auto-transfer. Radiation oncologist Monoenergetic Plus data handling is as easy as standard 120 kV images but benefits from better tumor contrast. Patient Acquisition is as simple as standard 120 kV acquisition, although acquisition time takes longer (10–15 seconds) than single energy acquisition. 1 Available on SOMATOM Definition Edge and SOMATOM Definition Edge Plus 17 Dual Energy CT cookbook · Conclusion Conclusion From the initial planning to treatment adaptation, target delineation is one of the most decisive parts of the RT workflow, and it is well documented that it can be subject to large interobserver variations. With Dual Energy CT, we now have the opportunity, during this crucial task, to make target delineation clearer and more reproducible, potentially by improved CNR and object demarcation without having an impact on radiation therapy workflow. 18 Theory · Dual Energy CT cookbook Theory Dual Energy Monoenergetic formula Monoenergetic formula is described for your further reference or research. μx (E) = xp • ƒp(E) + xc • ƒc (E) μx (E): Attenuation coefficient of a material x, at a certain energy E. xp, xc : Constants, depending only on material properties (like atomic number and density), which scale the Photoelectric effect and the Compton effect, respectively. ƒp(E), ƒc (E): Functions which represent Photoelectric effect (i.e., absorption of X-rays) and Compton effect (scattering), respectively. These two functions don’t depend on the materials, but only on the energies. ƒp(E), ƒc (E): Are known from fitting experimental data. Only unknowns are : xp, xc That’s why, in principle, two different measurements at two different energies are sufficient to calculate these xp and xc constants. Since ƒp(E), ƒc (E) don’t depend on the material but only on the energy, we can write different equations for different materials (x, y, z). What changes will be only the unknown constants, not the Photoelectric and Compton functions themselves. μx (E) = xp • ƒp(E) + xc • ƒc (E) μy (E) = yp • ƒp(E) + yc • ƒc (E) μz (E) = zp • ƒp(E) + zc • ƒc (E) Thus, Photoelectric and Compton functions are explicit and are written in terms of μy (E) and μz (E). – μy (E) = yp • ƒp(E) + yc • ƒc (E) → ƒp(E) = μy (E) • zc μz (E) • yc yp • zc yc • zp – (E) = zp • ƒp(E) + zc • ƒc (E) → ƒc (E) = μz (E) • yp – μy (E) • zp μz yp •zc yc • zp – If substituted, the new, rewritten forms of ƒp (E) and ƒc (E) in our first equation (for the material x) are: μx (E) = xp • ƒp(E) + xc • ƒc (E) → μx (E) = ay • μy (E) + az • μz (E) What we have just performed is a change of variables. We progressed from expressing μx (E) in terms of its Photoelectric and Compton contributors to expressing μx (E) in terms of μy (E) and μz (E) that is to say, in terms of the attenuation coefficient of two other materials. This is called – two-basis material decomposition. 19 Dual Energy CT cookbook · Theory Graphically, this can be understood as a change of coordinate system: ƒc (E) μx (E) = xp • ƒp(E) + xc • ƒc (E) μx (E) xc xp ƒp(E) ƒc (E) Another material (y) will be displayed as μx (E) another vector with different compositions: μy (E) = yp • ƒp(E) + yc • ƒc (E) yc μy (E) yp ƒp(E) Another material (z) will be displayed as another vector with different compositions: ƒc (E) μz (E) μz (E) = zp • ƒp(E) + zc • ƒc (E) μx (E) zc μy (E) zp ƒp(E) < We can express any vector in terms of two other vectors: μz (E) μx (E) = ay • μy (E) + az • μz (E) μx (E) az μy (E) ay 20 Theory · Dual Energy CT cookbook With this equation: μx (E) = ay • μy (E) + az • μz (E) the only unknowns are now ay and az , which are respectively the contributors of basis material y and basis material z. Doing two scans at two different energies, we have: Elow = ay • μy (Low) + az • μz (Low) Ehigh = ay • μy (High) + az • μz (High) We are free to choose any couple of (known) basis material that we wish. In our approach we choose for the sake of simplicity: y: water, z: iodine. We know the attenuation coefficients of these materials at different energies. Solving the system and substituting the HU to the attenuation coefficient, remembering that ( HUx (E) = μx (E) – μwater(E) 1000 ) • μwater(E) we obtain: HUx (E) = wx,low(E) • HUx (Low) + wx,high(E) • HUx (High) Where wx,low(keV) + wx,high(keV) = 1 and the weight are just a combination of ay and az that we calculated before. So basically, moving the monoenergetic slider will perform a mixed series but with a wider range. Dual Energy Monoenergetic Plus [3] Besides the established technique of Monoenergetic imaging, Siemens Healthineers has developed Monoenergetic Plus to avoid noise increase at lower calculated energies, which is a known drawback of virtual monoenergetic images. At low keV a regional spatial frequency-based recombination of the high signal at lower energies and the superior noise properties at medium energies is performed to optimize CNR in cases with Monoenergetic Plus images. The CNR and low-contrast detectability were evaluated. 21 Dual Energy CT cookbook · References References The creation of this cookbook was supported by the Siemens Healthineers key experts: Yohei Watanabe Fernando Barral Christian Hofmann Global Marketing Southern Europe Senior Scientist Manager for Business Manager Predevelopment CT Radiation Oncology for Radiation Oncology for Radiation Oncology Siemens Heathcare GmbH Siemens Healthcare GmbH Siemens Healthcare GmbH [1] McCollough CH, Leng S, Yu L, Fletcher JG. [5] Sushma Agrawal et al.: Late effects of cancer Dual- and multi-energy CT: Principles, technical treatment in breast cancer survivors, South approaches, and clinical applications. Radiology, Asian Journal of Cancer, vol 3, p 112–115, 2014. 276 (3): 637-53. 2015. https://www.ncbi.nlm. nih.gov/pubmed/26302388 [6] Poortmans P, Aznar M, Bartelink H. Quality indicators for breast cancer: revisiting historical [2] Lifeng Yu et al, Dual-Energy CT–Based evidence in the context of technology changes. Monochromatic Imaging, American Journal of Semin Radiat Oncol ;22:29–39 (2012) Roentgenology, vol 199, no. 5, p 9–15, 2012. https://www.ncbi.nlm.nih.gov/pmc/articles/ [7] Janssen-Heijnen ML, van Steenbergen LN, PMC3230639/ Voogd AC, Tjan-Heijnen VC, Nijhuis PH, Poortmans PM, et al. Small but significant excess [3] Grant KL, Flohr TG, Krauss B, Sedlmair M, mortality compared with the general population Thomas C, Schmidt B. Assessment of an for long-term survivors of breast cancer in the advanced image-based technique to calculate Netherlands. Ann Oncol ;25:64–8 (2014) virtual monoenergetic computed tomographic images from a dual-energy examination to [8] Birgitte V et al, ESTRO consensus guideline improve contrast-to-noise ratio in examinations on target volume delineation for elective using iodinated contrast media. Invest Radiol, radiation therapy of early stage breast cancer. 49:586–92.2014 Journal of Radiotherapy and Oncology 114: 3–10 (2015) [4] Michael T, Christian C et al.: Can dual-energy CT improve the assessment of tumor margins in oral cancer? Journal of Oral Oncology, Volume 50, Issue 3, p 221–227, 2014. https://www.ncbi.nlm.nih.gov/pubmed/24373911 22 Read more · Dual Energy CT cookbook Read more from our series Don´t miss out on other guides for Imaging in RT with practical tips & tricks for the implementation and use of our solutions – intended for experts and novice users alike. CT Imaging for RT planning 4D CT cookbook 2.0 A guide to 4D CT imaging 4D CT cookbook 2.0 A guide to 40 CT imaging in RT in RT siemens-healthineers.com/ radiotherapy/ct-for-rt .... MR Imaging for RT planning MR-integrated Workflows in Radiation Therapy for MAGNETOM systems siemens-healthineers.com/ radiotherapy/mri-for-rt/ mri-training 23 On account of certain regional limitations of sales rights Note: Any technical data contained in this document may and service availability, we cannot guarantee that all vary within defined tolerances. Original images always products included in this brochure are available through lose a certain amount of detail when reproduced. the Siemens Healthineers sales organization worldwide. Availability and packaging may vary by country and are The information presented in this cookbook is for subject to change without prior notice. Some / all of illustration only and is not intended to be relied upon the features and products described herein may not be by the reader for instruction as to the practice of available in the United States. medicine. Any healthcare practitioner reading this information is reminded that they must use their own The information in this document contains general learning, training and expertise in dealing with their technical descriptions of specifications and options as individual patients. well as standard and optional features which do not always have to be present in individual cases, and which This material does not substitute for that duty and is may not be commercially available in all countries. not intended by Siemens Healthineers to be used for any purpose in that regard. The Operating Instructions must Due to regulatory reasons their future availability always be strictly followed when operating the CT system. cannot be guaranteed. Please contact your local Siemens Healthineers organization for further details. Siemens Healthineers reserves the right to modify the design, packaging, specifications, and options described herein without prior notice. 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