4D CT Cookbook - A Guide to 4D Lung CT Imaging for Radiotherapy Planning

A Guide to 4D Lung CT Imaging for Radiotherapy Planning

4D CT cookbook 2.1 A guide to 4D CT imaging in RT 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 4D CT cookbook 2.1 · Foreword and Contributors Foreword Because organs move with the respiratory This is because the field of irradiation must motion, CT images of the chest and abdomen be wider than the actual size of the target to may contain artifacts that create problems account for the target's motion. Patients can with reproducibility and image interpretation. benefit from precise margins or "mid-vent" dose planning. The organs in the chest and abdomen move periodically and repetitively according to Addressing the challenge of motion in radiation respiratory motion. Image artifacts and therapy is a key factor in the continuum of treatment risks can be avoided if respiratory cancer care and External Beam Radiation motion can be precisely detected and if Therapy (EBRT). synchronized imaging or irradiation is available. This booklet describes current solutions and Especially when a linear accelerator is used for tips and tricks to implement 4D imaging in tumor treatment, normal tissue around the the clinical routine. We encourage you to offer target may be unnecessarily exposed to radiation feedback that will help us support the fight if the tumor is located in a moving organ. against cancer. Contributors Peter Albeck Qvistgaard Dr. Carsten Grohmann Bess Sutherland Nigel Middlebrook Head of Radiography Collaboration partner Senior Medical Physicist Regional Medical and Pre-treatment, Physicist/ Radiation Icon Group, Australia Physics Lead, Aarhus University Oncologist Icon Group, Australia Hospital Trent Aland Ulf Labsik Director of Medical Physics Senior Product Manager Icon Group, Australia Varian Medical Systems 2 Content · 4D CT cookbook 2.1 Content Breathing recording system Motivation 4 Technologies 4 Patient selection Motivation 5 Patient condition checklist 5 Breathing curve evaluation and examples 5 Acquisition Motivation 6 Scan protocol 6 Tips for initial 4D CT protocol setup 6 Respiratory motion management decision tree 8 Tips for dose conflict management 9 Direct i4D 11 Reconstruction Motivation 13 Gating parameters 13 Reconstruction parameters 14 4D image types, advantages and disadvantages 14 Contouring target and organs-at-risk (OAR) Motivation 15 Automatic preprocessing 15 What 4D images are used? 16 Quality Assurance (QA) for Varian RGSC Motivation 18 Step by step introduction 18 Conclusion 23 References 24 Read more from our series 27 3 4D CT cookbook 2.1 · Breathing recording system Breathing recording system Motivation The image quality of a 4D CT dataset depends largely on accurate scan parameters (see the ”Acquisition” section) and good synchronization between the acquisition and the patient’s breathing curve. To help achieve high image quality, devices are used to track and record the patient’s breathing and provide this information to the user and the CT scanner. Technologies Respiratory There are different breathing recording systems available on the market that use different gating / technologies. Here are some examples1: signal • detection RPM / RGSC (Varian Medical Systems) Infrared tracking camera and a reflective marker block placed on the patient • Anzai (Anzai Medical) Mechanical detection using an elastic belt around the patient with a pressure sensor • Sentinel 4D CT (C-RAD) Laser-based optical detection of thoracic excursions • GateCT (Vision RT) Surface guidance technology with tracking of the patient via single stereo camera unit The most commonly used are optical detection systems, because some patients are uncomfortable wearing a belt around the thorax or abdomen or breathing into a spirometer. Positioning • The marker block’s position should be “flat” (i.e., not tilted) because many lung cancer patients don’t have sufficient thorax motion to produce a safe and robust signal (amplitude of more than 2–3 mm). • The block should be positioned caudally from the sternum (as close as possible) and sufficiently near the target. Try to find the best location for the strongest signal. "Strongest signal" is depending on the patient's way of breathing. This can be below the sternum on the abdomen/belly or on the lower part of sternum. Tips and tricks • Some systems require an accuracy check and – if needed – a calibration prior to the first procedure each day. This procedure must be performed prior to patient setup on the table. • Make sure that the marker block is visible in the tracked area throughout the entire scan. • Make sure to mark the position of the block in a way that it can be placed at the exact same spot for accurate rescan or gated treatment. O SIEMENS ealthineers OMATOM 96 Figure 2: Figure 1: Example of Positioning the patient marker block positioning 1 The information shown herein refers to products of 3rd party manufacturers and thus are in their regulatory responsibility. Please contact the 3rd party manufacturer for further information. 4 Patient selection · 4D CT cookbook 2.1 Patient selection Motivation Even with modern scan and reconstruction techniques, 4D CT scans are prone to artifacts and uncertainties in the observed tumor motion. In the worst case, the scan has to be aborted and then repeated, leading to extra dose for the patient. Patient selection and optional breathing training are important factors in reducing these problems. Breathing curve Patient condition checklist evaluation and examples Patients with the following conditions are less The breathing curve should be monitored on suitable for a 4D CT: the breathing curve recording system or at the Patients who feel uncomfortable lying down scanner console if a compatible device is used • for long periods (Varian or Anzai). If any of the factors below • Patients with pathological respiration patterns: occur, there may be many image artifacts. for example, Biot’s ataxic breathing, Cheyne- • Is the amplitude too low? (3A: ideal breathing Stokes curve, 3B: amplitude too low) • Patients with very long respiration periods • Is there significant irregular breathing (less than six breath cycles per minute) during the 4D recording? (3C) • Patients with frequent severe coughing, or • Does coughing occur during 4D CT recording? who are very fatigued and fall asleep during (3D) the exam • If a quality indicator is available, does it • Patients who breathe too fast (i.e., 30 bpm) show poor periodicity? (3E) → training is needed to breathe reasonably fast 3A 3B 3C 3D 3E Periodicity - Poor Tips and tricks • It’s important that the patient’s breathing pattern is fairly regular, and coaching may make their breathing pattern more regular and lead to good 4D CT images. • If the patient is coached for the 4D CT, coaching should be repeated for the treatment situation. Otherwise, systematic errors can be introduced: for example, the anatomy shown in the 4D CT will not represent the anatomy at treatment. If coaching is not offered, tell the patient to relax and breathe normally. • A trial run before the scan is recommended: for example, how the table moves, how automatic patient instruction is provided. • The optimal setup for the breathing curve recording system should be performed for the best quality indicator and amplitude. Some systems have a feature that coaches the patient: the patient can watch their breathing curve on a screen and try to follow a defined pattern. • Some devices offer visual feedback to patients e.g. via a screen that can be used for training but also during examination. This direct feedback could help the patient to stay relaxed and guides the breathing procedure well (for example, via the Varian VCD (Visual Coaching Device)). 5 4D CT cookbook 2.1 · Acquisition Acquisition Motivation The selection of the right acquisition technique and scan parameters are crucial in order to minimize artifacts and to provide the right type of image needed for subsequent treatment planning. We describe both conventional and adaptive acquisition along with their respective pros and cons. Conventional 4D CT (spiral scan) 4D CT with Direct i4D1, 2, 3 (adaptive sequential scan) Figure 4A: Figure 4B: Example of a 4D spiral scan Example of a scan with Direct i4D Radiation Comparable dose between Direct i4D and 4D spiral scan dose Scanning No adaption Fully adaptive to patients breathing frequency and approach amplitude Recon- No adaptation in reconstruction Adaptive reconstruction based on average amplitude struction and average breathing cycle Result Sensitive to variation in Robust against variation in breathing patterns. breathing patterns [3] Reduces 85% of artifacts caused by the acquisition of an incomplete breathing cycle.[1] Scan protocol When a conventional scan protocol is selected (for example, RT_Resp), the estimated respiration rate (“Est. respiration time”) plays an important role in setting the scan parameters (e.g. pitch and rotation time for spiral scanning). If these parameters are set correctly, every voxel is scanned for at least one breathing cycle. Scanning too fast can result in incomplete breathing cycle information. Tips for initial 4D CT protocol setup Step 1) Adapt CTDIvol When setting up a 4D CT protocol on a new SOMATOM CT scanner, it is important to understand the correct comparison value. When firstly setting up the new CT system, it is recommended to take the CTDIvol from the previous CT system as a baseline for comparison. To adapt the CTDIvol, please change eff. mAs or mAs/rot depending on the SOMATOM CT scanners so that the CTDI displayed on CT scanner console is comparable as starting point as Image quality for the single phase / multiphase reconstruction is defined in eff. mAs or mAs/rot. 1 Direct i4D is the world's first intelligent 4D CT technology that adapts to the patient breathing, exclusively available for selected scanners. 2 Systematic shift of the whole respiratory curve to a higher or lower position over many breathing cycles. 3 Table mounted RGSC is recommended to minimize baseline drift compared to other methods (e.g. wall mounted camera). 6 Acquisition · 4D CT cookbook 2.1 There are different parameters for tube current displayed as below. a) mAs/rot I ⋅ Trot = b) Effective mAs = I ⋅ Trot ⋅α (I : mA, Trot: rotation time, α: recon angle) Step 2) Change FAST Adjust parameter FAST Adjust is a functionality that assists the user to solve possible X-ray tube conflicts. The following X-ray tube conflicts may occur: a) Image Quality conflict: If the optimal tube current exceeds the maximum tube current that can be delivered by the tube and the generator, the optimal tube current cannot be applied. In this case, image quality may be reduced and hence a Image Quality conflict occurs. b) Tube Load conflict: A tube load conflict occurs if the X-ray tube temperature is expected to exceed the system limits during the planned scan range. By standard setting, the FAST Adjust Lower Limit is defined as 25% of max mAs. In practice it means that, in case of Image Quality or Tube Load conflicts occurs, by activating the FAST Adjust functionality the system will try to solve the conflict by reduicng the mAs of up to 25% in the regions where the conflict occurs. In 4D CT scans the shoulder area is the most common region where a conflict occurs (due to the high-attenuation nature of the shoulders). Nevertheless, since this anatomical region is typically not relevant for a 4D CT study, it is recommended to increase the FAST Adjsut Lower Limit from 25% to 50%. A practical example is provided in the picture below: + Eam Designer Scan Protocols 1. Select Protocols 2 Modify Protocols 3. Confirm Changes Protocol Scan Favorites General Scan Dose Timing Confa Physio Scan Contrast Recon Favorites General Recon Recon&GO Image Impression Recon Box Physio Recon Auto Tasking Infine Options Fix/Replace Scan/Recon Config x Scen/Recon Meno Check&GO Check800 check& GO Check&GO Onentation Scan Start Scan Ref. FAST Agust Lower Metal Detector mage Type L'mit max. mAs [%] RTP Restatduty Vuliun Montagement [lokaty] Tcpogram ON Start Button Respira cly Motion Coverdye MER Coronel Step 3) Change CAREDose modulation strength configuration Another way to influence dose of a 4DCT scan is to change the CAREDose modulation strength, which can be found at CAREDose 4D Configuration. We recommend to use “average”. Only use “weak” if you experience that the Image Quality for large patients is “too good” for the given task. 7 4D CT cookbook 2.1 · Acquisition Respiratory motion management decision tree After registering the patient, it’s important to select the correct estimated respiration when using conventional 4D CT scanning. The decision tree helps to obtain an accurate acquisition from among conventional 4D CT scanning and adaptive 4D CT scanning (Direct i4D). Check the average RPM (Respiration Per Minute) rate displayed at the trigger subtask card for at least 10 breathing cycles Is Direct i4D1 available? No Is the overall curve / estimated respiration rate stable (for example, 11, 10, 10, 10, 11; or less than 1 RPM average deviation)? V Yes Yes No Wait several minutes for breathing to stabilize. If still irregular provide breathing coaching. Is the breathing stable enough now? Yes No If it’s unstable, for example, 11, 10, 9, 7, 9, 10, What is the average respiration rate? 9 … then select >6 (due to the 7 RPM measured) to proceed conventional 4D CT. Otherwise, consider a different method (e.g. breath-hold CT or free- breathing CT). More than 6 Less than 6 Select the estimated respiration rate in the Offer breathing coaching to increase the rate to menu (>6, >9, >12) that includes the lowest more than 6. Or consider a different method recorded respiration rate, or utilize FAST 4D1 (free breathing / deep inspiration) that automatically selects appropriate protocol. Direct i4D2 Conventional 4D CT Breath-hold or free-breathing CT 1 FAST 4D automatically estimates the breathing rate to adapt protocol (e.g. rotation time) 2 Direct i4D is the world's first intelligent 4D CT technology that adapts to the patient breathing, exclusively available for selected scanners. 8 Acquisition · 4D CT cookbook 2.1 Tips and tricks • Some breathing recording systems allow an online display of the breathing curve on the CT system; other systems require the breathing curve to be imported in order to reconstruct the breathing phases. Direct i4D requires a system capable of online display of the breathing curve in order to adapte the scan in real time. • On most SOMATOM CT scanners, it’s sufficient to enter the patient’s respiration rate; the scanner then automatically calculates the optimal pitch /rotation time combination. • Please keep in mind that importing the breathing curve is required with an open interface. • The breathing curve should be given the patient’s ID on the breathing recording system. This allows the file to be easily found and identified in systems where a manual import is required (this isn’t required for the online methods). • If a Varian device is used with an open interface, we recommend recalculating the peaks on the Varian device by checking “Automatic phase recalculation” and then using time-based reconstruction on the Siemens Healthineers CT. • SOMATOM CT systems with FAST 4D automatically detect the respiration rate from selected breathing recording systems and set the optimal scan parameters accordingly requires online mode. Tips for dose conflict management A so called “dose conflict notification” appears when protocol Preconditions Respiratory Parameter Adaption adaptations are required due to e.g. wrong patient positioning, Scan Parameter Check large patients and/or a fast breathing of the patient. DOP Scanning not possible Invalid parameters. Change parameters! Protocol management of 4DCT can be challenging and for the reduction of potential dose conflicts certain the following FAST Adjust Configured Applied measures can be considered. Max. MAS 25% 61 Exam Time 60 $ 177.08 Topogram too short Dose Modulation requires Topogram data Perform new Topogram, adapt the scan range, or press GOI Respiratory Motion CTDIvol (32 cm) 81.13 mGy DLP 5.254.7 mGy cm Elf MAS 61 KV 120 Exposure Time 176.84 Scanning not possible 9 4D CT cookbook 2.1 · Acquisition Step 1) Patient positioning before scan To ensure the optimized dose for every patient, a dose modulation based on the topogram scan (CAREDose 4D) is applied during the 4DCT scan acquisition. Therefore, if the patient is not positioned correctly, a dose conflict can be introduced or the patient might be over-irradiated. To avoid this problem, it is imperative to position the patient in the center of the gantry. X-ray tube X-ray tube Patient centered Patient too high Patient Patient Detector Detector Patient is positioned in the center, Patient positioning is too high. During the CAREDose4D provides optimized dose topogram scan, the system assumes a larger according to the Quality reference mAs. patient size due to the increased distance between the patient and the detector. CARE Dose4D then selects a higher dose compared to a patient positioned in the center. Step 2) Parameter configuration after topogram scan A dose conflict might also be triggered after the topogram scan due to a larger patient size or an increased breathing rate. To maintainimage quality in both scenarios, the tube capacity might be too high to perform the scan. In these two cases, the following solutions could help you solve the dose conflict: 1. When the dose conflict arises, check whether the shoulders are included in the scan range. If possible, try to avoid including the shoulder area since, due to the high-attenuation, this area typically requires a high dose in order to achieve the desired image quality. In general, try to use a smaller scan range centered around the region of the tumor, especially for large patients. 2. If it is not desired to exclude the shoulder area or it is still not possible to solve the x-ray tube conflict, try to Est. Respiratory Rate subsequently select lower breath rates until the scan can be performed / the dose conflict is solved. Auto Auto > 6 rpm This solution allows for a longer scan range but > 9 rpm compromises on temporal resolution. > 12 rpm > 15 rpm > 18 rpm 10 Acquisition · 4D CT cookbook 2.1 Direct i4D1 Werner et al[1] describe a novel 4D CT acquisition called Direct i4D. This intelligent 4D CT sequential acquisition adapts to the patient's breathing pattern in real time. This helps to address the following challenges: 1) Irregular Breathing Frequency When the breathing frequency is too irregular, there can be artifacts related to the acquisition of an incomplete breathing cycle. This happens when there was an incomplete breathing cycle acquired for every position of the patient. 8 17 12 8 8 17 12 8 Figure 5: Figure 6: Interpolation artifacts with conventional 4D CT spiral Scan with Direct i4D (simulated) Conventional 4D CT Direct i4D With the conventional 4D CT, the respiratory Direct i4D monitors and analyzes the curve is just recorded in parallel to acquisition. respiratory curve of the patient online. Scan duration at every position is fixed. (e.g. Direct i4D adapts the scan duration (x-ray 5s ≙ 12 bpm) When the breath rate drops to on time) to the current patient breathing e.g. 8 bpm (≙ 7.5 s cycle length) artifacts frequency in real time to assure that which origin from incomplete breathing cycles a complete breathing cycle is acquired (e.g. interpolation artifacts) cannot be avoided. at every position. 1 Direct i4D is the world's first intelligent 4D CT technology that adapts to the patient breathing, exclusively available for selected scanners. 11 4D CT cookbook 2.1 · Acquisition 2) Irregular Amplitude When the breathing amplitude is too irregular, there can be artifacts originating from variation in breathing amplitude (e.g. stack artifacts). This happens when there are, for example, shallow breathing cycles or very deep inspiration cycles in the breathing patterns of the patient. 14 14 14 14 14 14 14 Figure 7: Figure 8: Interpolation artifacts with conventional 4D CT spiral Scan with Direct i4D (simulated) Conventional 4D CT Direct i4D In conventional 4D CT the scan does not react Direct i4D recognizes online the patients average to the patients breathing amplitudes. Moreover breathing amplitude and adapts the acquisition the multiphase reconstruction of conventional to that. Moreover, the intelligent multiphase 4D CT does not account for irregular breathing reconstruction of Direct i4D evaluates how the amplitudes of the patient. Stack artifacts and patient was breathing on average and adapts double structures are the consequence. the reconstruction accordingly. “Direct i4D simplifies the 4D CT workflow and produces excellent results even for patients with irregular breathing patterns. Therefore, it helps to determine the best possible individual dose plan for RT.” Peter Albeck Qvistgaard Head of Radiography and Pre-treatment, Aarhus University Hospital 12 Reconstruction · 4D CT cookbook 2.1 Reconstruction Motivation Reconstruction can be challenging due to patient's different respiration patterns. Inappropriate reconstruction parameters could cause changes in tumor location between the reconstructed phases due to image artifacts. With Direct i4D,the intelligent multiphase reconstruction evaluates how the patient was breathing on average and adapts the reconstruction accordingly to address patient's different respiratory patterns. Gating parameters CT scanners from Siemens Healthineers offer two approaches for sorting images. Below we list their pros and cons. For example, time-based reconstruction has been applied to stereotactic body radiation therapy (SBRT) planned on the mid-ventilation phase. Sync Possible Technique, Adjust devices pros and cons % (Time based Reconstruction) Anzai The breathing cycle is divided Varian into equal time points. RPM / RGSC Closely depicts the actual movement over time. Allows calculation of midventilation phase. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Prone to breathing irregularities or inconsistent breathing patterns that leads to 4D CT artifacts. % In, % Ex (Amplitude based Reconstruction) V Anzai The breathing cycle is divided into Varian equal sections according to the RPM / signal amplitude. Ex → In → RGSC Ex 100% In 100% Overall artifacts are fewer when Ex 80% In 80% Ex 60% In 60% the patient has irregular breathing Ex 40% In 40% Ex 20% In 20% pattern. Ex 0% Maximum exhalation phase can be directly reconstructed. Not possible to read the actual movement of the tumor over time. Not suitable for midventilation phase. 13 4D CT cookbook 2.1 · Reconstruction Reconstruction parameters Two different reconstruction tasks are typically used in the 4D CT daily routine. The first is the Average CT. The Average CT is calculated based on the whole 4D CT (raw) dataset and represents the blurred motion image over the respiratory cycle. The second commonly performed task is to reconstruct the individual phases of the 4D CT dataset. We recommend 10 phases to be reconstructed in order to cover the entire respiration cycle. Kernel B30 / Qr40 Window Mediastinum FOV 500 mm / 600 mm (if needed) Slice thickness 1.5 mm Increment 1.5 mm iMAR Depends on the implants • Pacemaker • Spine implants • Thoracic coils • Shoulder implants 4D image types, advantages and disadvantages[2] 13A 13B 13C 13D 4D Average CT; calculated T-MaxIP; calculated as the T-MinIP; calculated as Gated phase as the average HU value over highest HU value over the the minimum HU value over (e.g., 10 phases the different 4D phases. different 4D phases. the different 4D phases. from 0 – 100%) Pros: HU stable, commonly Fastest form of Indicates position of Excellent view of tumor used for dose delineation, highlights tumor at all times. motion, sharp image for calculation. tumors that are hyperdense target delineation. ITV for compared to the more accurate contouring surrounding tissue. results than T-MaxIP. Cons: • Motion blurring Less accurate than Not for dose calculation. Not as smooth as Average • Not appropriate for the 10-phase overlap CT because noise level is target delineation. approach (ITV). higher unless higher Dose calculation is exposure is applied. • Using only Average less accurate than CT for contouring could Average CT. underestimate the tumor motion excursion. 14 Contouring target and organs-at-risk · 4D CT cookbook 2.1 Contouring target and organs-at-risk (OAR) Motivation After the reconstruction of the 4D CT dataset, the next step will be to contour the target volume and any relevant organs-at-risk. Traditional tools often require the user to contour slice-by-slice and phase-by-phase. This time-consuming process can be speeded up with state-of-the-art tools that use pre-processing for OAR contouring and propagation of contours across phases for fast target delineation. Modern tools can also offer insights into tumor movement patterns and help identify the midventilation phase. The workflow described here is based on use of syngo.via RT Image Suite. Automatic preprocessing With syngo.via RT Image Suite, the following steps are already completed by pre-processing before the case is even opened. For more details, please refer to the syngo.via or scanner user manual regarding setup of automatic preprocessing. Structure Templates Liver Current Lung Left Lung Right CTRT, 1/13/2014 Spinal Cord Planning CTRTIS Prior 01 MRRAS 2014 Au Tunking Auta Taodoray Tilages Prior 02 Ade Diagn Descris ptous Exatired body Part CT PET, 1/9/2014 PETCTRTIS Prior 03 Close , CTRT, 1/2/2014 Structure SETRTIS Figure 14A: Figure14B: Figure 14C: The correct structure Once the scan is finished, auto-contouring is triggered and Has a previous study template is auto- contours are ready when the study is opened in syngo.via. already been performed? matically selected If so, the previous dataset at the scanner. is automatically loaded in the series navigator (remote prefetching). 15 4D CT cookbook 2.1 · Contouring target and organs-at-risk What 4D images are used? [2] The selection of the dataset for contouring largely depends on the motion mitigation technique that will be used in the treatment, (free-breathing, gated, breath-hold). Below is an overview of the different datasets and their pros and cons. Pros Cons T-MaxIP • No specific software required • No tumor motion assessment • Faster than ITV • Not accurate at soft tissue boundaries • Larger PTV (tumor motion included in whole) ITV • Small tumors and large motion • Dedicated software needed (Internal Target or hysteresis in for fast workflow Volume) motion • Larger PTV (tumor motion included Retrospective in whole) Midventilation [3] • Smaller GTV & PTV (tumor • Dedicated software needed motion included for fast workflow probabilistically in margins) • Not suitable with large hysteresis DIBH • Spare the dose to heart, • Patient compliance ~75% (deep inspiration coronary arteries, and lung due breath-hold) to increased distance between target and heart and to reduced lung density [4] Prospective • No specific software required Mid- • This represents the tumor in its timeaveraged position over the Tumor Curve 2 x venti- respiratory cycle. The midventilation approach can help reduce StrutturePOI NowStrutture! lation the PTV, leading to potentially decreased toxicity [3]. Studies [5] Head-Feet Amplitude Leh Rght Anpalude Anterior Pesteder Aopitude 0 phase indicate that, by applying smaller target volume margins, this Phase Closest to Midpassion 60 In Tumor Trajectory Delance do Midposition method can potentially increase the number of patients eligible for SBRT. Figure 15: Tumor trajectory curve shows the closest position for Midventilation. 16 Contouring target and organs-at-risk · 4D CT cookbook 2.1 Mid- • syngo.via RT Image Suite visualizes the quantitative 3D tumor trajectory and identifies the venti- phase lying closest to the mid-position, making it an ideal solution for introducing this lation method into the clinical routine. phase • Contouring on the mid-ventilation phase and applying appropriate margins for the individual patient’s tumor motion can also help with locally advanced cancer patient cases, because the tumors and, thus, the irradiated volumes are large, increasing the risk of toxicity. The margin expansion can then be tailored to what is required for the specific patient, based on the tumor motion. T-MaxIP • T-MaxIP is a projection of the highest HU value over the respiratory phases onto a 3D image at each voxel position. Deep • DIBH is a technique for scanning immediately after the inspiration plateau is reached. Inspiration Where spiral scans are used, the entire lung can be acquired during a single breath-hold. Breath- • The respiratory gating device is only used for monitoring the respiratory curve. Hold (DIBH) ITV • ITV is a “sum” of the GTV from all the phases. Tumor motion is covered with complete accuracy, and further consideration of the treatment strategy may be required for motion mitigation (for example, compression after large motion is indicated in the tumor trajectory). Propagate to All Tumor Curve 2 x Show Movement P181 long pall 3.0 130f 3 50% Ex Structure/POI : NewStructure1 Create ITV P1B1 long pall 3.0 8301 25% Ex Head-Fout Amplitude 0.7 cm Leht-Right Amplitude Erase Contours P1B1 long pall 3.0 B301 0% In Anterior-Posterior Amplitude 02 cm Duplicate P181 long pall 3.0 B30f 25% In Phase Closest to Midposition 60 In Turner Trajectory Distance to Midposition Delete v. P181 long pall 3.0 B30f 50% In Lock P1B1 long pall 3.0 B30f 75% In Figure 16A: After the semi-automated target delineation, contours are propagated to the other phases. 160 Ex 00 Cx 60 Ex 40 Ex 20 Ex DEx 0in 20 In 40 In 50 In 80 In 100 In Only use AD data That is binned equidistant in time to dieily midventilation phasel : OK Figure 16B: Figure 16C: After approximately 15 seconds, Tumor trajectory for further image contours have been propagated assessment (e.g., decision support for and displayed (red dots) along treatment with a suitable motion mitigation with ITV (blue). technique, e.g., abdominal compression). 17 4D CT cookbook 2.1 · Quality Assurance Quality Assurance (QA) for Varian RGSC Motivation Quality assurance (QA) tests must be performed to ensure consistent and accurate performance of the Varian RGSC system. Shi et al[6] provide recommendations on daily, monthly, and annual QA of a couch mounted RGSC system based on the author’s experience, but also urges clinical physicists to establish their own clinical QA standards which are “optimised for the needs of their clinic and available tools”[1]. With this section, recommendation of QA for RGSC system in conjunction with the SOMATOM Confidence for 4DCT and DIBH treatments are introduced. Step 1: Calibration (Verification) The purpose of the calibration is to make sure that the Varian RGSC system receives the correct positioning signal. In this section, the steps of calibration procedure are described for wall / ceiling mounted camera as well as table mounted camera. Wall / ceiling mounted camera Table mounted camera (9 points calibration) (1 point calibration) 1) To take the couch plane into consideration 1) Make sure that the calibration board is for calibration procedure, a 9 step calibration aligned to the CT isocenter at point 1. is needed. 2) Start calibration program for point 1. 2) Make sure that the calibration board is 3) The system automatically indicates that aligned to the CT isocenter at point 1. calibration is passed or failed. In case 3) Start calibration program from point 1 of failure, please try again. to point 9. 4) The system automatically indicates that the calibration has passed or failed. In case of failure, please try again. 1 5 3 O 5 7 VARÍAN 78 9 1 Feet IZ Figure 17 A, B: Figure 17 C: Example positions of marker block during calibration 1 point calibration in case of table mounted camera. in case of 9 points calibration. Reflector block is positioned at point 1 on calibration board. 18 Quality Assurance · 4D CT cookbook 2.1 Tips and tricks • The reflector block is required to be at isocenter height during calibration. • It is recommended that the calibration always be performed on a surface that is flat and level with the couch top, such as a flat wooden board. • A cardboard box or a foam block can induce an angle on the calibration board. This may introduce calibration errors. • Check expected positions during calibration. A range of movement (≥3 mm)in vertical position may indicate an expected baseline drift. X Flat board to achieve height Calibration board placed on un-even foam block Step 2: Motion learning, period and amplitude It is intended to check that the RGSC can learn the motion, and the period and amplitude match baselines. 1) Place the marker block on Varian motion phantom at the isocenter. 2) Care must be taken with the positioning of the marker block due to the angulation of the motion platform in the Varian motion phantom. 3) Learn the breathing patterns of the Varian phantom on the RGSC. 4) Guidelines are ~1.6 (± 0.2) cm amplitude and 5.8 (± 0.2) sec period (The period may slower with the low battery level). 5) If the time of the measurement is getting slower than the above, please consider to exchange the new battery. Learning Breathing Pattern Reflector block on Varian motion phantom Figure 18: Learning breathing pattern 19 4D CT cookbook 2.1 · Quality Assurance Step 3: Baseline drift evaluation Baseline drift is an effect that the longitudinal position is changed over the table movement. If there is a large (e.g. more than 6 mm) baseline drift, position of the treatment couch shall be adjusted to compensate for the drift so that the changes in the couch position can correspond to the baseline drift in the tumor motion (target margin). As the baseline drift can be smaller if the direction of table motion coincides precisely with the level of calibration, how to evaluate the baseline drift is described. 1) Use weighted bed if possible in order to reproduce the practical setup. 2) Place reflector block at the isocenter of the external lasers 3) Learn the breathing patterns of the Varian motion phantom on the Varian RGSC. 4) Move the couch into the bore (~600 mm longitudinal move) and wait for 2–3 breathing phases. Do not relearn the breathing pattern. 5) Check the baseline drift described on Varian RGSC user interface and check if the value is less than 2 mm. If the value is higher than that, please reconsider to re-calibrate (step 1). ---- Baseline MMM Peroduay Baseline Drift [cm] 0.3 Figure 19: Measurement of the period and amplitude; orange line shows there is a small baseline drift (left). Check baseline drift with Varian motion phantom: Hint • Baseline drift is often unavoidable due to the inherent sag of the CT couch, particularly with patient weight added. • The user may choose to weight the couch during the calibration to counteract the effect of the patient weight. In this case, the baseline drift would be greater without weight during movement. • It is important to remember that the Varian RGSC is a surrogate for patient breathing and any baseline drift caused by the CT couch movement will not be seen on the treatment linac. 20 Quality Assurance · 4D CT cookbook 2.1 Step 4: Image reconstruction and Phase binning The purpose of this step is to make sure that the tracked amplitude displayed on Varian RGSC Marker Marker is corresponding to the amplitude on image reconstruction. K 1) Use reflector block on Varian motion phantom. A small marker is placed on the center of the top cross of the reflector block so this position could be seen for The difference between these measurements. measurements is the amplitude 2) 4D CT Scan for the phantom. 3) Reconstructed with 100% Ex and 0% Ex sagital or coronal (to measure the amplitude) with thin slice (e.g. 2 mm) so that the marker can be visible with less partial volume effect. 4) Open the 100% Ex and 0% Ex series with the 100 Ex 0 Ex Dicom viewer. 5) Use distance tool to measure the distance between surface of the table to the small Figure 20: Phase binning amplitude measurement maker on 100% Ex and 0% Ex 6) Compare the value between motion range displayed on Varian RGSC and measurement Motion Range on Varian RGSC – (100% Ex – 0% Ex) <2 mm If there are more than 2 mm, please consider re-calibration (step 1) 40 $3 98 Set 1 [1] Inspiration [s] 2.5 13.01 cm 11.65 cm Expiration [s] 2.4 Motion Range [cm] 1.38 Example shows the motion range difference between image evaluation and detection from Varian RGSC. In this case, difference in the image reconstruction 13.01 – 11.65 = 1.36 cm Varian RGSC motion range = 1.38 cm Therefore, the Step 4 is passed in this case. 21 4D CT cookbook 2.1 · Quality Assurance Hint: Alternative Camera calibration method for wall-mounted or ceiling-mounted cameras On some scanners the couch doesn’t move exactly parallel to the couch top surface, especially when there is weight on the couch. In this case you might observe a baseline drift that increases the further you move the couch inside the scanner bore. In the following steps we suggest an alternative way of calibrating the wall or ceiling-mounted RGSC camera. Instead of using the calibration board and placing the reflector block on different points on the couch top, the couch is used to reach different longitudinal positions: Step 1: Place a reference weight onto the couch top, e.g. 70 kg. Step 2: Start the calibration process in the Varian RGSC application. Step 3: Place the reflector block into a reference position for the verification, e.g. scanner isocenter or room laser isocenter. > Acquire position 1. Step 4: Place the reflector block approximately 10 – 20 cm left and right of the reference position > Acquire positions 2 and 3. Step 5: Move the couch at least 20 cm into the scanner bore. Step 6: Place the reflector block into three positions with a relative distance of approximately 10 – 20 cm (left, center, right). > Acquire positions 4, 5 and 6. Step 7: Move the couch at least 20 cm into the scanner bore. Step 8: Place the reflector block into three positions with a relative distance of approximately 10–20 cm (left, center, right). > Acquire positions 7, 8 and 9. Step 9: Confirm the calibration. 22 Conclusion · 4D CT cookbook 2.1 Conclusion This booklet attempts to provide guidance for Siemens Healthineers SOMATOM CT users. The information provided is intended to support your entire clinical team in optimizing your workflow and growing your practice, while improving the prognosis for cancer patients throughout the world. Finally, we look forward to hearing your feedback and suggestions so that we at Siemens Healthineers can continuously support you in delivering excellent care to your patients. The creation of this cookbook was supported by the Siemens Healthineers key experts: Dr. Christian Hofmann Yohei Watanabe Annie Bruder Senior Scientist Global Lead Marketing Global Marketing Predevelopment CT Manager for Manager for for Radiation Oncology Radiation Oncology Radiation Oncology Siemens Healthcare GmbH Siemens Heathcare GmbH Siemens Heathcare GmbH 23 4D CT cookbook 2.1 · References References [1] Werner R et al. Intelligent 4D CT sequence [4] Bruzzaniti V et al. Dosimetric and clinical scanning (i4DCT): Concept and performance advantages of deep inspiration breath-hold evaluation. Med Phys. Aug;46(8):p 3462–3474 (DIBH) during radiotherapy of breast cancer. (2019) Journal of Experimental & Clinical Cancer Research, vol. 32, p. 1–7, (2013). [2] Hutchinson A et al. 4DCT radiotherapy for NSCLC; a review of planning methods. Journal [5] Peulen H et al. Midventilation-based PTV of Radiotherapy in Practice, vol. 14, issue 1, margins in Stereotactic Body Radiotherapy p. 70–79, (2015). (SBRT): A clinical evaluation. Radiotherapy and Oncology 110, (2014) 511–516, (2014) [3] Wolthaus JW et al. Midventilation CT scan construction from four-dimensional respiration- [6] Shi C, Tang X, Chan M. Evaluation of the correlated CT scans for radiotherapy planning of new respiratory gating system. Precis Radiat lung cancer patients. Int. J. Radiation Oncology Oncol. ;1(4):127–133, (2017). Biol. Phys., vol. 65, no. 5, pp. 1,560–1,571, (2006). 24 Notes · 4D CT cookbook 2.1 Notes 25 25 4D CT cookbook 2.1 · Notes Notes 26 Read more · 4D CT cookbook 2.1 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 Dual Energy CT cookbook DirectDensity cookbook A guide to Monoenergetic Dual Energy CT cookbook DirectDensity cookbook Plus imaging in RT guide to Monoenergetic Plus imaging in RT A guide to personalized CT imaging in RT A guide to personalized CT imaging In RT radiotherapy/ct-for-rt radiotherapy/ct-for-rt ..... 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Page 14 MRI in Radiosurgery for Trigeminal Neuralgia Krzysztof Ślosarek, et al. radiotherapy/mri-for-rt/ hot-topics/mri-in-radiation- Page 18 Clinical Implementation and Evaluation of MR-only RT Planning for Brain Tumors T1w MPRAGE David Roberge and Jean-Charles Côté mri-training therapy Page 24 Clinical Implementation of MR-guided RT for Prostate Cancer in the Halcyon-System Mandy Zimmermann, et al. Page 33 A Fully Automated, End-to-End Prostate MRI Workflow Solution Incorporating Dot, Ultrashort Biparametric Imaging and Deep-Learning-based Detection, T2w CISS Classification, and Reporting David J. Winkel, et al. Not for distribution in the US ealthineers 27 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. Please contact your local Siemens Healthineers sales representative for the most current information. Siemens Healthineers Headquarters Siemens Healthcare GmbH Henkestr. 127 91052 Erlangen, Germany Phone: +49 9131 84-0 Published by Siemens Healthcare GmbH · Printed in Germany · 9431 0920 · ©Siemens Healthcare GmbH, 2020