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  • 1
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    Keywords: measurement ; radiotherapy ; Germany ; CT ; IMAGES ; ACCURACY ; RESOLUTION ; validation ; MRI ; SEQUENCE ; treatment ; MAGNETIC-RESONANCE ; TARGET ; stereotactic radiotherapy ; REQUIRES ; REGISTRATION ; LOCALIZATION ; positron emission tomography ; HEAD ; NECK ; SPECT ; treatment planning ; PET ; head and neck ; BRAIN IMAGES ; SPATIAL DISTORTION
    Abstract: CT, MRI, PET and SPECT provide complementary information for treatment planning in stereotactic radiotherapy. Stereotactic correlation of these images requires commissioning tests to confirm the localization accuracy of each modality. A phantom was developed to measure the accuracy of stereotactic localization for CT, MRI, PET and SPECT in the head and neck region. To this end, the stereotactically measured coordinates of structures within the phantom were compared with their mechanically defined coordinates. For MRI, PET and SPECT, measurements were performed using two different devices. For MRI, T1- and T2-weighted imaging sequences were applied. For each measurement, the mean radial deviation in space between the stereotactically measured and mechanically defined position of target points was determined. For CT, the mean radial deviation was 0.4 +/- 0.2 mm. For MRI, the mean deviations ranged between 0.7 +/- 0.2 mm and 1.4 +/- 0.5 rum, depending on the MRI device and the imaging sequence. For PET, mean deviations of 1.1 +/- 0.5 mm and 2.4 +/- 0.3. mm were obtained. The mean deviations for SPECT were 1.6 +/- 0.5 mm and 2.0 +/- 0.6 mm. The phantom is well suited to determine the accuracy of stereotactic localization with CT, MRI, PET and SPECT in the head and neck region. The obtained accuracy is well below the physical resolution for CT, PET and SPECT, and of comparable magnitude for MRI. Since the localization accuracy may be device dependent, results obtained at one device cannot be generalized to others
    Type of Publication: Journal article published
    PubMed ID: 12587905
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  • 3
    Keywords: human ; ALGORITHM ; CT ; SYSTEM ; TISSUE ; ACCURACY ; treatment ; BEAM ; treatment planning ; MONTE-CARLO ; DOSE CALCULATIONS ; MULTIPLE COULOMB SCATTERING
    Abstract: For proton dose calculations in heterogeneous media, it was shown in a previous work that the conventional pencil beam approach based on pathlength scaling does not properly account for scattering effects in nonwater media (Szymanowski and Oelfke 2002 Phys. Med. Biol. 47 3313-30). A two-dimensional scaling method was therefore introduced, which is able to predict with high accuracy the propagation of proton pencil beams both along the depth and the lateral directions in inhomogeneous media. In order to integrate this improved pencil beam algorithm in a CT based treatment planning system, two CT calibration curves are needed. The first one relates the Hounsfield numbers to the relative stopping powers, as for the conventional pencil beam approach. The second curve is to relate the Hounsfield numbers to the material-specific lateral scaling factors. The purpose of this work is to provide the CT calibration curves needed for the integration of the pencil beam algorithm featuring the two-dimensional scaling method. Similarly to as suggested by Schneider et al (1996 Phys. Med. Biol. 41 111-24) for the calibration curve in terms of stopping powers, we follow a stoichiometric procedure to get the calibration curve in terms of material-specific lateral scaling factors. The calibration curves for a CT scanner of the type Siemens Somatom Plus 4 are obtained from the analytical calculation of the CT Hounsfield numbers, relative stopping powers and material-specific lateral scaling factors for human biological tissues
    Type of Publication: Journal article published
    PubMed ID: 12701891
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  • 4
    Keywords: radiotherapy ; Germany ; LUNG ; ALGORITHM ; CT ; IMAGES ; imaging ; SYSTEM ; TIME ; PATIENT ; treatment ; SIGNAL ; NUMBER ; REGION ; Jun ; COMPUTED-TOMOGRAPHY ; MOTION ; RECONSTRUCTION ; FEASIBILITY ; ORGAN MOTION ; RE ; INCREASE ; DIAPHRAGM ; PHASE ; SIZE ; RESPIRATORY MOTION ; cone beam CT ; respiratory gating
    Abstract: A new online imaging approach, linac-integrated cone beam CT (CBCT), has been developed over the past few years. It has the advantage that a patient can be examined in their treatment position directly before or during a radiotherapy treatment. Unfortunately, respiratory organ motion, one of the largest intrafractional organ motions, often leads to artefacts in the reconstructed 3D images. One way to take this into account is to register the breathing phase during image acquisition for a phase-correlated image reconstruction. Therefore, the main focus of this work is to present a system which has the potential to investigate the correlation between internal (movement of the diaphragm) and external (data of a respiratory gating system) information about breathing phase and amplitude using an inline CBCT scanner. This also includes a feasibility study about using the acquired information for a respiratory-correlated 4D CBCT reconstruction. First, a moving lung phantom was used to develop and to specify the required methods which are based on an image reconstruction using only projections belonging to a certain moving phase. For that purpose, the corresponding phase has to be detected for each projection. In the case of the phantom, an electrical signal allows one to track the movement in real time. The number of projections available for the image reconstruction depends on the breathing phase and the size of the position range from which projections should be used for the reconstruction. The narrower this range is, the better the inner structures can be located, but also the noise of the images increases due to the limited number of projections. This correlation has also been analysed. In a second step, the methods were clinically applied using data sets of patients with lung tumours. In this case, the breathing phase was detected by an external gating system (AZ-733V, Anzai Medical Co.) based on a pressure sensor attached to the patient's abdominal region with a fixation belt. The comparison of the reconstructed 4D CBCT images and the corresponding 4D CT images used for the treatment planning provides the required information for the calculation of possible setup errors
    Type of Publication: Journal article published
    PubMed ID: 16723776
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  • 5
    Keywords: OPTIMIZATION ; Germany ; COMPLEX ; COMPLEXES ; DOMAIN ; RE ; THIN-PLATE SPLINES ; DEFORMATIONS ; elastic registration ; NONRIGID REGISTRATION ; LANDMARK ; MEDICAL IMAGES
    Abstract: Deformable registration is an important application in medical image analysis and processing. We propose a physics-based parametric approach for deformable image registration, where non-rigid transformations are computed using an irregular grid of control points distributed within the image domain. The image is modelled as a three-dimensional (3D) homogeneous infinite elastic medium. It is assumed that a Gaussian-shaped force is applied at every control point, where the strengths, directions and influence areas of the forces as well as the positions of the control points are considered as free parameters whose optimization leads to maximization of the similarity measure between the images to be registered. For optimization, a computationally efficient Levenberg-Marquardt method is used. The proposed approach has certain advantages over traditional landmark-based methods or the registration methods based on regulargrids, for example B-splines, since comparable results can be achieved by using less control points. Experimental results with 3D clinical images demonstrate that our method is capable of successfully coping with complex registration tasks
    Type of Publication: Journal article published
    PubMed ID: 16394344
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  • 6
    Keywords: OPTIMIZATION ; radiotherapy ; Germany ; imaging ; treatment ; TARGET ; treatment planning ; MOTION ; IMRT ; methods ; NUCLEAR ; technique ; function ; dose uncertainties ; VARIABLES ; SET ; BEAM PROFILES ; INCORPORATING ORGAN MOVEMENTS
    Abstract: Radiotherapy treatment planning is associated with uncertainties. Examples are uncertainties in the tumour location due to organ movement or the inter/intra observer variability in target definition. Different approaches to incorporate uncertainties into IMRT optimization have been proposed. In this note, we point out a relation between two previously published methods: the coverage probability approach and the concept of optimizing the expectation value of an objective function that depends on a set of random variables. Both concepts are generally different, but turn out to be equivalent in special cases
    Type of Publication: Journal article published
    PubMed ID: 17110760
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  • 7
    Keywords: ABNORMALITIES, ALGORITHM, ALIGNMENT, chest, CT, evaluation, Germany, IMAGE REGISTRATION, imaging, IN
    Abstract: Recently it has been shown that regional lung perfusion can be assessed using time-resolved contrast-enhanced magnetic resonance (MR) imaging. Quantification of the perfusion images has been attempted, based on definition of small regions of interest (ROIs). Use of complete lung segmentations instead of ROIs could possibly increase quantification accuracy. Due to the low signal-to-noise ratio, automatic segmentation algorithms cannot be applied. On the other hand, manual segmentation of the lung tissue is very time consuming and can become inaccurate, as the borders of the lung to adjacent tissues are not always clearly visible. We propose a new workflow for semi-automatic segmentation of the lung from additionally acquired morphological HASTE MR images. First the lung is delineated semi-automatically in the HASTE image. Next the HASTE image is automatically registered with the perfusion images. Finally, the transformation resulting from the registration is used to align the lung segmentation from the morphological dataset with the perfusion images. We evaluated rigid, affine and locally elastic transformations, suitable optimizers and different implementations of mutual information (MI) metrics to determine the best possible registration algorithm. We located the shortcomings of the registration procedure and under which conditions automatic registration will succeed or fail. Segmentation results were evaluated using overlap and distance measures. Integration of the new workflow reduces the time needed for post-processing of the data, simplifies the perfusion quantification and reduces interobserver variability in the segmentation process. In addition, the matched morphological data set can be used to identify morphologic changes as the source for the perfusion abnormalities
    Type of Publication: Journal article published
    PubMed ID: 17301453
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  • 8
    Keywords: radiotherapy ; Germany ; THERAPY ; PATIENT ; REDUCTION ; analysis
    Abstract: The influence of artefacts due to metal implants on the range of ion beams is investigated, using a geometrically well-defined head and pelvic phantom together with inserts from steel, titanium and tungsten. The ranges along various beam paths including artefacts were calculated from the TPS and compared to known calculations for phantoms without any insert. In the head phantom, beams intersecting the streak artefacts lead to errors in the range of around or below 1%, which is mainly due to a cancellation of various effects. Beams through the metal or close to it show an underestimation of 3.5% of the range for tungsten. For the pelvic phantom, a large underestimation of the range is observed for a lateral path through the metal insert. In the case of tungsten and steel, range errors of - 5% and - 18% are observed, respectively. Such beam paths are typically used for pelvic tumours in radiotherapy with ion beams. For beams in the anterior - posterior direction through the inserts, an overestimation of ion ranges of up to 3% for titanium and 8% for steel is expected, respectively. Beam paths outside the metal insert show a large cancellation for the lateral beams ( leading to errors of around 1% only) and somewhat higher errors for anterior - posterior beams ( around 3% for titanium and 6% for steel). The analysis of CT data of patients with dental implants of gold as compared to patients with healthy teeth also showed a significant effect of the artefacts on the distribution of HU in the data, namely a redistribution of HU to higher and lower values as compared to patients with healthy teeth. The corresponding mean range variation was a 2.5% reduction in the data with artefacts as compared to the data without artefacts. It is concluded that beam paths through metal implants should generally be avoided in proton and ion therapy. In this case, the underestimation of ion range due to artefacts alone may amount to 3% for dental fillings and up to 5% and 18% for hip prosthesis made of titanium and steel, respectively. It is important to note that the size of the metal inserts cannot be determined correctly from the images, so that a correction of the ranges in metal also leads to large uncertainties. Finally, it should be stressed that the stated relative deviations are strictly valid only for the investigated phantoms and can only give a rough estimate on the size of range uncertainties that may appear in real patients
    Type of Publication: Journal article published
    PubMed ID: 17228110
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  • 9
    Keywords: OPTIMIZATION ; ANGIOGENESIS ; APOPTOSIS ; CELLS ; GROWTH ; IRRADIATION ; proliferation ; radiotherapy ; SURVIVAL ; CELL ; CELL-PROLIFERATION ; Germany ; MODEL ; MODELS ; DENSITY ; imaging ; TISSUE ; NUCLEAR-MEDICINE ; radiation ; tumour ; TOLERANCE ; treatment ; DISTRIBUTIONS ; REQUIRES ; DOSE-RESPONSE ; PARAMETERS ; NORMAL TISSUE ; nuclear medicine ; OXYGEN ; radiosensitivity ; radiology ; RE ; cell proliferation ; computer simulation ; NUCLEAR ; quantitative ; FRACTIONATION ; CONTROL PROBABILITY ; PARAMETRIC VALIDATION ; RADIOTHERAPY IN-VIVO ; TENSION
    Abstract: Optimization of treatment plans in radiotherapy requires the knowledge of tumour control probability (TCP) and normal tissue complication probability (NTCP). Mathematical models may help to obtain quantitative estimates of TCP and NTCP. A single-cell-based computer simulation model is presented, which simulates tumour growth and radiation response on the basis of the response of the constituting cells. The model contains oxic, hypoxic and necrotic tumour cells as well as capillary cells which are considered as sources of a radial oxygen profile. Survival of tumour cells is calculated by the linear quadratic model including the modified response due to the local oxygen concentration. The model additionally includes cell proliferation, hypoxia-induced angiogenesis, apoptosis and resorption of inactivated tumour cells. By selecting different degrees of angiogenesis, the model allows the simulation of oxic as well as hypoxic tumours having distinctly different oxygen distributions. The simulation model showed that poorly oxygenated tumours exhibit an increased radiation tolerance. Inter-tumoural variation of radiosensitivity flattens the dose response curve. This effect is enhanced by proliferation between fractions. Intra-tumoural radiosensitivity variation does not play a significant role. The model may contribute to the mechanistic understanding of the influence of biological tumour parameters on TCP. It can in principle be validated in radiation experiments with experimental tumours
    Type of Publication: Journal article published
    PubMed ID: 17671335
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  • 10
    Keywords: OPTIMIZATION ; Germany ; THERAPY ; ALGORITHM ; imaging ; RISK ; NUCLEAR-MEDICINE ; TIME ; QUALITY ; REDUCTION ; treatment ; FIELD ; TARGET ; DISTRIBUTIONS ; RADIATION-THERAPY ; NUMBER ; BEAM ; MULTILEAF COLLIMATOR ; nuclear medicine ; IMRT ; IMPLEMENTATION ; radiology ; SINGLE ; THERAPIES ; DOSE DISTRIBUTIONS ; WEIGHT ; development ; BEAM THERAPY ; ROTATION THERAPY ; NUCLEAR ; technique ; UNIT ; comparison ; GRADIENT ; DIRECT APERTURE OPTIMIZATION ; DYNAMIC MULTILEAF COLLIMATION ; TOMOTHERAPY
    Abstract: In this paper, we propose an optimization concept for a rotation therapy technique which is referred to as arc-modulated cone beam therapy (AMCBT). The aim is a reduction of the treatment time while achieving a treatment plan quality equal to or better than that of IMRT. Therefore, the complete dose is delivered in one single gantry rotation and the beam is modulated by a multileaf collimator. The degrees of freedom are the field shapes and weights for a predefined number of beam directions. In the new optimization loop, the beam weights are determined by a gradient algorithm and the field shapes by a tabu search algorithm. We present treatment plans for AMCBT for two clinical cases. In comparison to step-and-shoot IMRT treatment plans, it was possible by AMCBT to achieve dose distributions with a better dose conformity to the target and a lower mean dose for the most relevant organ at risk. Furthermore, the number of applied monitor units was reduced for AMCBT in comparison to IMRT treatment plans
    Type of Publication: Journal article published
    PubMed ID: 17664597
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