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  • DKFZ Publication Database  (22)
  • treatment  (11)
  • OPTIMIZATION  (10)
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  • DKFZ Publication Database  (22)
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  • 1
    Keywords: radiation ; OPTIMIZATION ; treatment ; TECHNOLOGY ; inverse planning ; ONCOLOGY ; RADIATION ONCOLOGY
    Type of Publication: Book chapter
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  • 2
    Keywords: OPTIMIZATION ; SPECTRA ; radiotherapy ; evaluation ; MODEL ; THERAPY ; SYSTEM ; SYSTEMS ; VOLUME ; RISK ; radiation ; TIME ; PATIENT ; BASE ; treatment ; TARGET ; RADIATION-THERAPY ; adaptive triangulation ; clustering techniques ; multi-criteria optimization ; representative pareto solutions
    Abstract: Radiation therapy planning is often a tightrope walk between dangerous insufficient dose in the target volume and life threatening overdosing of organs at risk. Finding ideal balances between these inherently contradictory goals challenges dosimetrists and physicians in their daily practice. Todays inverse planning systems calculate treatment plans based on a single evaluation function that measures the quality of a radiation treatment plan. Unfortunately, such a one dimensional approach cannot satisfactorily map the different backgrounds of physicians and the patient dependent necessities. So, too often a time consuming iterative optimization process between evaluation of the dose distribution and redefinition of the evaluation function is needed. In this paper we propose a generic multi-criteria approach based on Pareto's solution concept. For each entity of interest - target volume or organ at risk - a structure dependent evaluation function is defined measuring deviations from ideal doses that are calculated from statistical functions. A reasonable bunch of clinically meaningful Pareto optimal solutions are stored in a data base, which can be interactively searched by physicians. The system guarantees dynamic planning as well as the discussion of tradeoffs between different entities. Mathematically, we model the inverse problem as a multi-criteria linear programming problem. Because of the large scale nature of the problem it is not possible to solve the problem in a 3D-setting without adaptive reduction by, appropriate approximation schemes. Our approach is twofold: First, the discretization of the continuous problem results from an adaptive hierarchical clustering process which is used for a local refinement of constraints during the optimization procedure. Second, the set of Pareto optimal solutions is approximated by an adaptive grid of representatives that are found by a hybrid process of calculating extreme compromises and interpolation methods
    Type of Publication: Journal article published
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  • 3
    Keywords: OPTIMIZATION ; radiotherapy ; Germany ; THERAPY ; ALGORITHM ; ALGORITHMS ; imaging ; NUCLEAR-MEDICINE ; radiation ; SEQUENCE ; treatment ; DISTRIBUTIONS ; RADIATION-THERAPY ; DIFFERENCE ; NUMBER ; BEAM ; DELIVERY ; STRATEGIES ; INTENSITY-MODULATED RADIOTHERAPY ; MULTILEAF COLLIMATOR ; SEGMENTS ; nuclear medicine ; IMRT ; APPROXIMATION ; MAPS ; radiology ; PROGRAM ; THERAPIES ; radiation therapy ; intensity modulated radiotherapy ; NUCLEAR ; technique ; BEAMS ; MEDICINE ; ERROR ; CONSTRAINTS
    Abstract: In inverse planning for intensity-modulated radiotherapy ( IMRT), the fluence distribution of each treatment beam is usually calculated in an optimization process. The delivery of the resulting treatment plan using multileaf collimators ( MLCs) is performed either in the step-and-shoot or sliding window technique. For step-and-shoot delivery, the arbitrary beam fluence distributions have to be transformed into an applicable sequence of subsegments. In a stratification step the complexity of the fluence maps is reduced by assigning each beamlet to discrete intensity values, followed by the sequencing step that generates the subsegments. In this work, we concentrate on the stratification for step-and-shoot delivery. Different concepts of stratification are formally introduced. In addition to already used strategies that minimize the difference between original and stratified beam intensities, we propose an original stratification principle that minimizes the error of the resulting dose distribution. It could be shown that for a comparable total number of subsegments the dose-oriented stratification results in a better approximation of the original, unsequenced plan. The presented algorithm can replace the stratification routine in existing sequencer programs and can also be applied to interpolated plans that are generated in an interactive decision making process of multicriteria inverse planning programs
    Type of Publication: Journal article published
    PubMed ID: 17881818
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  • 4
    Keywords: CANCER ; carcinoma ; PROSTATE ; QUANTIFICATION ; DISEASE ; TISSUE ; QUALITY ; MRI ; SPECTROSCOPY ; prostate cancer ; LOCALIZATION ; PATTERN ; pattern recognition ; postprocessing ; proton MR spectroscopic imaging
    Abstract: RATIONALE AND OBJECTIVES: The aim of this study was to assess (1) automated analysis methods versus manual evaluation by human experts of three-dimensional proton magnetic resonance spectroscopic imaging (MRSI) data from patients with prostate cancer and (2) the contribution of spatial information to decision making. MATERIALS AND METHODS: Three-dimensional proton MRSI was applied at 1.5 T. MRSI data from 10 patients with histologically proven prostate adenocarcinoma, scheduled either for prostatectomy or intensity-modulated radiation therapy, were evaluated. First, two readers manually labeled spectra using spatial information to identify the localization of spectra and neighborhood information, establishing the reference set of this study. Then, spectra were labeled again manually in a blinded and randomized manner and evaluated automatically using software that applied spectral line fitting as well as pattern recognition routines. Statistical analysis of the results of the different approaches was performed. RESULTS: Altogether, 1018 spectra were evaluable by all methods. Numbers of evaluable spectra differed significantly depending on patient and evaluation method. Compared to automated analysis, the readers made rather binary decisions, using information from neighboring spectra in ambiguous cases, when evaluating MRSI data as a whole. Differences between anatomically blinded and unblinded evaluation were larger than differences between evaluations using blinded data and automated techniques. CONCLUSIONS: An automated approach, which evaluates each spectrum individually, can be as good as an anatomy-blinded human reader. Spatial information is routinely used by human experts to support their final decisions. Automated procedures that consider anatomic information for spectral evaluation will enhance the diagnostic impact of MRSI of the human prostate.
    Type of Publication: Journal article published
    PubMed ID: 22578226
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  • 5
    Keywords: OPTIMIZATION ; DISTRIBUTIONS ; RADIATION-THERAPY ; PENALTY
    Abstract: Common problems in inverse radiotherapy planning are localized dose insufficiencies like hot spots in organs at risk or cold spots inside targets. These are hard to correct since the optimization is based on global evaluations like maximum/minimum doses, equivalent uniform doses or dose-volume constraints for whole structures. In this work, we present a new approach to locally correct the dose of any given treatment plan. Once a treatment plan has been found that is acceptable in general but requires local corrections, these areas are marked by the planner. Then the system generates new plans that fulfil the local dose goals. Consequently, it is possible to interactively explore all plans between the locally corrected plans and the original treatment plan, allowing one to exactly adjust the degree of local correction and how the plan changes overall. Both the amount (in Gy) and the size of the local dose change can be navigated. The method is introduced formally as a new mathematical optimization setting, and is evaluated using a clinical example of a meningioma at the base of the skull. It was possible to eliminate a hot spot outside the target volume while controlling the dose changes to all other parts of the treatment plan. The proposed method has the potential to become the final standard step of inverse treatment planning.
    Type of Publication: Journal article published
    PubMed ID: 23442519
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  • 6
    Keywords: OPTIMIZATION ; radiotherapy ; tumor ; ALGORITHM ; ALGORITHMS ; INFORMATION ; SYSTEM ; SYSTEMS ; RISK ; treatment ; ASSOCIATION ; FORM ; TARGET ; NO ; DISTRIBUTIONS ; EQUIVALENT ; RADIATION-THERAPY ; HEAD ; NECK ; head and neck ; CONVEX-SETS ; equivalent uniform dose ; inverse planning ; optimization constraints ; projection onto convex sets ; PROJECTIONS
    Abstract: Optimization algorithms in inverse radiotherapy planning need information about the desired dose distribution. Usually the planner defines physical dose constraints for each structure of the treatment plan, either in form of minimum and maximum doses or as dose-volume constraints. The concept of equivalent uniform dose (EUD) was designed to describe dose distributions with a higher clinical relevance. In this paper, we present a method to consider the EUD as an optimization constraint by using the method of projections onto convex sets (POCS). In each iteration of the optimization loop, for the actual dose distribution of an organ that violates an EUD constraint a new dose distribution is calculated that satisfies the EUD constraint, leading to voxel-based physical dose constraints. The new dose distribution is found by projecting the current one onto the convex set of all dose distributions fulfilling the EUD constraint. The algorithm is easy to integrate into existing inverse planning systems, and it allows the planner to choose between physical and EUD constraints separately for each structure. A clinical case of a head and neck tumor is optimized using three different sets of constraints: physical constraints for all structures, physical constraints for the target and EUD constraints for the organs at risk, and EUD constraints for all structures. The results show that the POCS method converges stable and given EUD constraints are reached closely. (C) 2003 American Association of Physicists in Medicine
    Type of Publication: Journal article published
    PubMed ID: 14528955
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  • 7
    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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  • 8
    Keywords: IRRADIATION ; radiotherapy ; Germany ; VOLUME ; CYCLE ; treatment ; BREAST ; IONIZATION ; DELIVERY ; MOTION ; IMRT ; ORGAN MOTION
    Abstract: For intensity modulated radiotherapy (IMRT) of deep-seated tumours, dosimetric variations of the original static dose profiles due to breathing motion can be primarily considered as blurring effects known from conventional radiotherapy. The purpose of this dosimetric study was to clarify whether these results are transferable to superficial targets and to quantify the additional effect of fractionation. A solid polystyrene phantom and an anthropomorphic phantom were used for film and ion chamber dose measurements. The phantoms were installed on an electric driven device and moved with a frequency of 6 or 12 cycles per minute and an amplitude of 4 mm or 10 mm. A split beam geometry of two adjacent asymmetric fields and an IMRT treatment plan with 12 fields for irradiation of the breast were investigated. For the split beam geometry the dose modifications due to unintended superposition of partial fields were reduced by fractionation and completely smoothed out after 20 fractions. IMRT applied to the moving phantom led to a more homogeneous dose distribution compared to the static phantom. The standard deviation of the target dose which is a measure of the dose homogeneity was 10.3 cGy for the static phantom and 7.7 cGy for a 10 mm amplitude. The absolute dose values, measured with ionization chambers, remained unaffected. Irradiation of superficial targets by IMRT in the step-and-shoot technique did not result in unexpected dose perturbations due to breathing motion. We conclude that regular breathing motion does not jeopardize IMRT of superficial target volumes
    Type of Publication: Journal article published
    PubMed ID: 16510947
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  • 9
    Keywords: OPTIMIZATION ; radiotherapy ; RISK
    Abstract: In the multi-criteria optimization approach to IMRT planning, a given dose distribution is evaluated by a number of convex objective functions that measure tumor coverage and sparing of the different organs at risk. Within this context optimizing the intensity profiles for any fixed set of beams yields a convex Pareto set in the objective space. However, if the number of beam directions and irradiation angles are included as free parameters in the formulation of the optimization problem, the resulting Pareto set becomes more intricate. In this work, a method is presented that allows for the comparison of two convex Pareto sets emerging from two distinct beam configuration choices. For the two competing beam settings, the non-dominated and the dominated points of the corresponding Pareto sets are identified and the distance between the two sets in the objective space is calculated and subsequently plotted. The obtained information enables the planner to decide if, for a given compromise, the current beam setup is optimal. Hemay then re-adjust his choice accordingly during navigation. The method is applied to an artificial case and two clinical head neck cases. In all cases no configuration is dominating its competitor over the whole Pareto set. For example, in one of the head neck cases a seven-beam configuration turns out to be superior to a nine-beam configuration if the highest priority is the sparing of the spinal cord. The presented method of comparing Pareto sets is not restricted to comparing different beam angle configurations, but will allow for more comprehensive comparisons of competing treatment techniques (e. g. photons versus protons) than with the classical method of comparing single treatment plans
    Type of Publication: Journal article published
    PubMed ID: 21610294
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  • 10
    Keywords: CANCER ; PROSTATE ; QUANTIFICATION ; SYSTEM ; CONFORMAL RADIOTHERAPY ; EXPERIENCE ; RADIATION-THERAPY ; dynamic MRI ; ORGAN MOTION ; MOVEMENT ; CINE-MRI ; GLAND ; BEAM COMPUTED-TOMOGRAPHY ; INTRAFRACTION MOTION
    Abstract: To investigate prostate movement during deep breathing and contraction of abdominal musculature by means of dynamic MRI and analyze implications for image-guided radiotherapy of prostate cancer. A total of 43 patients and 8 healthy volunteers were examined with MRI. Images during deep respiration and during contraction of abdominal musculature (via a coughing maneuver) were obtained with dynamic two-dimensional (2D) balanced SSFP; 3 frames/s were obtained over an acquisition time of 15 s. Images were acquired in sagittal orientation to evaluate motion along both the craniocaudal (cc)-axis and anteroposterior (ap)-axis. Prostate motion was quantified semi-automatically using dedicated software tools. Respiratory induced mean cc-axis displacement of the prostate was 2.7 +/- 1.9 (SD) mm (range, 0.5-10.6 mm) and mean ap-axis displacement 1.8 +/- 1.0 (SD) mm (range, 0.3-10 mm). In 69% of the subjects, breathing-related prostate movements were found to be negligible (〈 3 mm). The prostate displacement for abdominal contraction was significantly higher: mean cc-axis displacement was max. 8.4 +/- 6.7 (SD) mm (range, 0.6-27 mm); mean anteroposterior movement was 8.3 +/- 7.7 (SD) mm (range, 0.7-26 mm). Dynamic MRI is an excellent tool for noninvasive real-time imaging of prostate movement. Further investigations regarding possible applications in image-guided radiotherapy, e.g., for individualized planning and in integrated linac/MRI systems, are warranted
    Type of Publication: Journal article published
    PubMed ID: 21713396
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