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  • ALGORITHM  (7)
  • 1
    Keywords: RISK ; segmentation ; radiation ; THERAPY ; ALGORITHM ; RADIATION-THERAPY ; therapy planning ; THERAPIES ; radiation therapy
    Type of Publication: Book chapter
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  • 2
    Keywords: IRRADIATION ; radiotherapy ; Germany ; LUNG ; THERAPY ; ALGORITHM ; CT ; imaging ; INFORMATION ; SYSTEM ; SYSTEMS ; EXPOSURE ; TISSUE ; computed tomography ; validation ; NUCLEAR-MEDICINE ; TIME ; PATIENT ; COMPLEX ; MARKER ; SIGNAL ; PERFORMANCE ; MARKERS ; REGION ; REGISTRATION ; LOCALIZATION ; COMPUTED-TOMOGRAPHY ; MOTION ; nuclear medicine ; GATED RADIOTHERAPY ; IMRT ; ORDER ; radiology ; RE ; THERAPIES ; breathing cycle ; methods ; NUCLEAR ; technique ; MUTUAL INFORMATION ; RESPIRATORY MOTION ; phantom ; ENGLAND ; PREDICT ; MAXIMIZATION ; tumor motion ; MEDICINE ; X-RAY ; particle therapy ; LIMITS ; POSITION ; CONE-BEAM CT ; LUNG-TUMORS
    Abstract: Respiratory motion limits the potential of modern high-precision radiotherapy techniques such as IMRT and particle therapy. Due to the uncertainty of tumour localization, the ability of achieving dose conformation often cannot be exploited sufficiently, especially in the case of lung tumours. Various methods have been proposed to track the position of tumours using external signals, e. g. with the help of a respiratory belt or by observing external markers. Retrospectively gated time-resolved x-ray computed tomography (4D CT) studies prior to therapy can be used to register the external signals with the tumour motion. However, during treatment the actual motion of internal structures may be different. Direct control of tissue motion by online imaging during treatment promises more precise information. On the other hand, it is more complex, since a larger amount of data must be processed in order to determine the motion. Three major questions arise from this issue. Firstly, can the motion that has occurred be precisely determined in the images? Secondly, how large must, respectively how small can, the observed region be chosen to get a reliable signal? Finally, is it possible to predict the proximate tumour location within sufficiently short acquisition times to make this information available for gating irradiation? Based on multiple studies on a porcine lung phantom, we have tried to examine these questions carefully. We found a basic characteristic of the breathing cycle in images using the image similarity method normalized mutual information. Moreover, we examined the performance of the calculations and proposed an image-based gating technique. In this paper, we present the results and validation performed with a real patient data set. This allows for the conclusion that it is possible to build up a gating system based on image data, solely, or ( at least in avoidance of an exceeding exposure dose) to verify gates proposed by the various external systems
    Type of Publication: Journal article published
    PubMed ID: 18495978
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  • 3
    Keywords: CANCER ; radiotherapy ; tumor ; COMBINATION ; Germany ; LUNG ; PROSTATE ; ALGORITHM ; CT ; imaging ; INFORMATION ; lung cancer ; LUNG-CANCER ; MASK ; TISSUE ; TIME ; PATIENT ; COMPLEX ; COMPLEXES ; CONTRAST ; treatment ; TARGET ; ACQUISITION ; EXPERIENCE ; VECTOR ; NUMBER ; prostate cancer ; PROSTATE-CANCER ; REGISTRATION ; BEAM ; DELIVERY ; HEAD ; CANCER-PATIENTS ; MULTILEAF COLLIMATOR ; treatment planning ; BODY ; CANCER PATIENTS ; LINEAR-ACCELERATOR ; RECONSTRUCTION ; IMRT ; PATIENT FIXATION ; IMPLEMENTATION ; INCREASE ; chordoma ; LEVEL ; methods ; fractionated stereotactic radiotherapy ; technique ; MUTUAL INFORMATION ; cancer research ; cone beam CT ; LANDMARK ; INCREASES ; CLINICAL IMPLEMENTATION ; ACCELERATOR ; WORKLOAD
    Abstract: ABSTRACT: BACKGROUND: The purpose of the study was the clinical implementation of a kV cone beam CT (CBCT) for setup correction in radiotherapy. PATIENTS AND METHODS: For evaluation of the setup correction workflow, six tumor patients (lung cancer, sacral chordoma, head-and-neck and paraspinal tumor, and two prostate cancer patients) were selected. All patients were treated with fractionated stereotactic radiotherapy, five of them with intensity modulated radiotherapy (IMRT). For patient fixation, a scotch cast body frame or a vacuum pillow, each in combination with a scotch cast head mask, were used. The imaging equipment, consisting of an x-ray tube and a flat panel imager (FPI), was attached to a Siemens linear accelerator according to the in-line approach, i.e. with the imaging beam mounted opposite to the treatment beam sharing the same isocenter. For dose delivery, the treatment beam has to traverse the FPI which is mounted in the accessory tray below the multi-leaf collimator. For each patient, a predefined number of imaging projections over a range of at least 200 degrees were acquired. The fast reconstruction of the 3D-CBCT dataset was done with an implementation of the Feldkamp-David-Kress (FDK) algorithm. For the registration of the treatment planning CT with the acquired CBCT, an automatic mutual information matcher and manual matching was used. RESULTS AND DISCUSSION: Bony landmarks were easily detected and the table shifts for correction of setup deviations could be automatically calculated in all cases. The image quality was sufficient for a visual comparison of the desired target point with the isocenter visible on the CBCT. Soft tissue contrast was problematic for the prostate of an obese patient, but good in the lung tumor case. The detected maximum setup deviation was 3 mm for patients fixated with the body frame, and 6 mm for patients positioned in the vacuum pillow. Using an action level of 2 mm translational error, a target point correction was carried out in 4 cases. The additional workload of the described workflow compared to a normal treatment fraction led to an extra time of about 10-12 minutes, which can be further reduced by streamlining the different steps. CONCLUSION: The cone beam CT attached to a LINAC allows the acquisition of a CT scan of the patient in treatment position directly before treatment. Its image quality is sufficient for determining target point correction vectors. With the presented workflow, a target point correction within a clinically reasonable time frame is possible. This increases the treatment precision, and potentially the complex patient fixation techniques will become dispensable
    Type of Publication: Journal article published
    PubMed ID: 16723023
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  • 4
    Keywords: radiotherapy ; Germany ; THERAPY ; ALGORITHM ; CT ; IMAGES ; imaging ; SYSTEM ; SYSTEMS ; ACCURACY ; SIMULATION ; MRI ; MAGNETIC-RESONANCE ; magnetic resonance imaging ; REGION ; Jun ; HEAD ; COMPUTED-TOMOGRAPHY ; SPATIAL DISTORTION ; DEVICES ; 2D ; RE ; SIZE ; MR-IMAGES
    Abstract: For the application of magnetic resonance imaging (MRI) in precision radiotherapy, image distortions must be reduced to a minimum to maintain geometrical accuracy. Recently, two-dimensional (2D) and three-dimensional (3D) algorithms for MRI-device-specific distortion corrections were developed by the manufacturers of MRI devices. A previously developed phantom (Karger C P et al 2003 Phys. Med. Biol. 48 211 - 21) was used to quantify and assess the size of geometrical image distortions before and after application of the 2D and 3D correction algorithm in the head region. Four different types of MRI devices with different gradient systems were measured. For comparison, measurements were also performed with two computed tomography (CT) devices. Mean distortions of up to 4.6 +/- 1.4 mm (maximum: 5.8 mm) were found prior to the correction. After the correction, the mean distortions were well below 2.0 mm in most cases. Distortions in the CT images were below or equal to 1.0 mm on average. Generally, the 3D algorithm produced comparable or better results than the 2D algorithm. The remaining distortions after the correction appear to be acceptable for fractionated radiotherapy
    Type of Publication: Journal article published
    PubMed ID: 16757858
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  • 5
    Keywords: radiotherapy ; Germany ; THERAPY ; ALGORITHM ; CT ; DIAGNOSIS ; IMAGES ; TOOL ; RISK ; RESOLUTION ; validation ; radiation ; TIME ; PATIENT ; IMPACT ; DOMAIN ; treatment ; FREQUENCY ; FREQUENCIES ; RADIATION-THERAPY ; REGISTRATION ; treatment planning ; THIN-PLATE SPLINES ; rectum ; DEFORMATIONS ; elastic registration ; correlation ; MUTUAL INFORMATION ; NONRIGID REGISTRATION ; SET ; COEFFICIENTS ; LANDMARK ; elastic image registration ; adaptive radiotherapy ; BRAIN SHIFT ; CORRELATION-COEFFICIENT ; DEFORMABLE IMAGE REGISTRATION ; MAXIMIZATION
    Abstract: Image registration has many medical applications in diagnosis, therapy planning and therapy. Especially for time-adaptive radiotherapy, an efficient and accurate elastic registration of images acquired for treatment planning, and at the time of the actual treatment, is highly desirable. Therefore, we developed a fully automatic and fast block matching algorithm which identifies a set of anatomical landmarks in a 3D CT dataset and relocates them in another CT dataset by maximization of local correlation coefficients in the frequency domain. To transform the complete dataset, a smooth interpolation between the landmarks is calculated by modified thin-plate splines with local impact. The concept of the algorithm allows separate processing of image discontinuities like temporally changing air cavities in the intestinal track or rectum. The result is a fully transformed 3D planning dataset (planning CT as well as delineations of tumour and organs at risk) to a verification CT, allowing evaluation and, if necessary, changes of the treatment plan based on the current patient anatomy without time-consuming manual re-contouring. Typically the total calculation time is less than 5min, which allows the use of the registration tool between acquiring the verification images and delivering the dose fraction for online corrections. We present verifications of the algorithm for five different patient datasets with different tumour locations ( prostate, paraspinal and head-and-neck) by comparing the results with manually selected landmarks, visual assessment and consistency testing. It turns out that the mean error of the registration is better than the voxel resolution (2 x 2 x 3 mm(3)). In conclusion, we present an algorithm for fully automatic elastic image registration that is precise and fast enough for online corrections in an adaptive fractionated radiation treatment course
    Type of Publication: Journal article published
    PubMed ID: 16985271
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  • 6
    Keywords: CANCER ; IRRADIATION ; radiotherapy ; COMBINATION ; Germany ; THERAPY ; ALGORITHM ; CT ; QUANTIFICATION ; VOLUME ; ACCURACY ; radiation ; PATIENT ; COMPLEX ; COMPLEXES ; treatment ; RADIATION-THERAPY ; PROSTATE-CANCER ; MODULATION ; DELIVERY ; HEAD ; NECK ; COMPUTED-TOMOGRAPHY ; treatment planning ; LINEAR-ACCELERATOR ; DEVICES ; PATIENT FIXATION ; technique ; UNIT ; cancer research ; EXTENT ; adaptation ; SCANS ; MOVEMENTS ; ACCELERATOR
    Abstract: Modern radiotherapy techniques such as intensity modulation are capable of generating complex dose distributions whose high dose areas tightly conform to the tumour target volume, sparing critical organs even when they are located in close proximity. This potential can only be exploited to its full extent when the accumulated dose actually delivered over the complete treatment course is sufficiently close to the dose computed on the initial CT scan used for treatment planning. Exact patient repositioning is mandatory, but also other sources of error, e.g. changes of the patient's anatomy under therapy, should be taken into account. At the German Cancer Research Center, we use a combination of a linear accelerator and a CT scanner installed in one room and sharing the same couch. it allows the quantification and correction of interfractional variations between planning and treatment delivery. in this paper, we describe treatments of prostate, paraspinal and head and neck tumours. All patients were immobilized by customized fixation devices and treated in a stereotactic setup For each patient, frequent CT scans were taken during the treatment course. Each scan was compared with the original planning CT using manual checks and automatic rigid matching algorithms. Depending on the individual case, the adaptation to variations was carried out offline after several fractions or in real-time between the CT scan and linac irradiation. We discuss the techniques for detecting and correcting interfractional errors and outline the procedural steps of a linac-CT scanner-supported radiation treatment course. (C) 2006 The British Institute of Radiology
    Type of Publication: Journal article published
    PubMed ID: 16980687
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  • 7
    Keywords: CANCER ; ALGORITHM ; RADIATION-THERAPY ; UNCERTAINTIES ; adaptive radiotherapy ; DEFORMABLE IMAGE REGISTRATION ; SETUP ERRORS
    Abstract: BACKGROUND: To analyse the frequency of re-planning and its variability dependent on the IGRT correction strategy and on the modification of the dosimetric criteria for re-planning for the spinal cord in head and neck IG-IMRT. METHODS: Daily kV-control-CTs of six head and neck patients (=175 CTs) were analysed. All volumes of interest were re-contoured using deformable image registration. Three IGRT correction strategies were simulated and the resulting dose distributions were computed for all fractions. Different sets of criteria with varying dose thresholds for re-planning were investigated. All sets of criteria ensure equivalent target coverage of both CTVs, but vary in the tolerance threshold of the spinal cord. RESULTS: The variations of the D95 and D2 in respect to the planned values ranged from -7% to +3% for both CTVs, and -2% to +6% for the spinal cord. Despite different correction vectors of the three IGRT strategies, the dosimetric differences were small. The number of fractions not requiring re-planning varied between 0% and 11% dependent on the applied IGRT correction strategy. In contrast, this number ranged between 32% and 70% dependent on the dosimetric thresholds, even though these thresholds were only gently modified. CONCLUSIONS: The more precise the planned dose needs to be maintained over the treatment course, the more frequently re-planning is required. The influence of different IGRT correction strategies, even though geometrically notable, was found to be of only limited relevance for the re-planning frequency. In contrast, the definition and modification of thresholds for re-planning have a major impact on the re-planning frequency.
    Type of Publication: Journal article published
    PubMed ID: 25112458
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