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  • radiation  (15)
  • 1
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    Springer Verlag
    Keywords: radiation ; OPTIMIZATION ; treatment ; TECHNOLOGY ; inverse planning ; ONCOLOGY ; RADIATION ONCOLOGY
    Type of Publication: Book chapter
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  • 2
    Keywords: radiotherapy ; CANCER ; THERAPY ; CT ; IMAGES ; radiation ; RADIATION-THERAPY ; NECK ; HEAD ; CT images ; NECK-CANCER ; head and neck cancer ; radiation therapy ; THERAPIES ; NECK CANCER
    Type of Publication: Book chapter
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  • 3
    Keywords: RADIATION-THERAPY ; LOCALIZATION ; DATABASE ; IMRT ; radiation ; SYSTEM ; THERAPY ; THERAPIES ; radiation therapy
    Type of Publication: Book chapter
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  • 4
    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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  • 5
    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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  • 6
    Keywords: CANCER ; radiotherapy ; tumor ; carcinoma ; Germany ; THERAPY ; CT ; FOLLOW-UP ; imaging ; SURGERY ; radiation ; PATIENT ; prognosis ; CONTRAST ; RADIATION-THERAPY ; chemotherapy ; DELIVERY ; AD ; ESOPHAGUS ; RANDOMIZED-TRIAL ; IMRT ; radiology ; GUIDANCE ; THERAPIES ; LIBRARIES ; chemoradiation ; radiation therapy ; CT SCANS ; LIBRARY ; ESOPHAGEAL CANCER ; IMAGE GUIDANCE ; JUNCTION ; ATRIAL-FIBRILLATION ; outcome ; GUIDED RADIOTHERAPY ; RADIOCHEMOTHERAPY ; POSITION ; SCAN ; STRATEGY ; LIMITATIONS ; Esophageal carcinoma
    Abstract: Background: Despite maximum therapy the prognosis of esophageal carcinoma still remains extremely poor. New treatment strategies including improved radiation therapy techniques promise better outcome by improving local control through precise dose delivery due to higher conformality. Case Report: A 62-year-old patient with locally advanced carcinoma of the gastroesophageal junction underwent definitive radiochemotherapy with intensity-modulated radiation therapy (IMRT). On positioning control with the in-room CT, the distal. esophagus, and hence the tumor, was found to be highly mobile exhibiting changes in position of up to 4 cm from fraction to fraction. Result: IMRT plans were created for various positions establishing a plan library to choose from as appropriate. CT scans were performed prior to each treatment fraction to clarify esophagus position in order to choose the adequate treatment plan. Conclusion. Image guidance was crucial in this unusual case of esophageal carcinoma. Without the information from position control CTs, the tumor would have received only about half the prescribed dose due to variations in position. For this specific case, in-room CT scans are probably superior to kilo- or megavoltage CTs due to the higher soft-tissue contrast enabling detection of positioning variation of the organ and offering the possibility to use the CT for treatment planning
    Type of Publication: Journal article published
    PubMed ID: 19714309
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  • 7
    Keywords: radiotherapy ; LUNG ; THERAPY ; ALGORITHM ; IMAGES ; RISK ; ACCURACY ; validation ; radiation ; PATIENT ; ASSOCIATION ; RADIATION-THERAPY ; UNCERTAINTY ; sensitivity ; DEFORMABLE IMAGE REGISTRATION ; ERRORS ; 4D CT IMAGES ; b-spline registration ; dose accumulation ; dose mapping ; fractionated radiation therapy
    Abstract: Purpose: In fractionated radiation therapy, image guidance with daily tomographic imaging becomes more and more clinical routine. In principle, this allows for daily computation of the delivered dose and for accumulation of these daily dose distributions to determine the actually delivered total dose to the patient. However, uncertainties in the mapping of the images can translate into errors of the accumulated total dose, depending on the dose gradient. In this work, an approach to estimate the uncertainty of mapping between medical images is proposed that identifies areas bearing a significant risk of inaccurate dose accumulation.Methods: This method accounts for the geometric uncertainty of image registration and the heterogeneity of the dose distribution, which is to be mapped. Its performance is demonstrated in context of dose mapping based on b-spline registration. It is based on evaluation of the sensitivity of dose mapping to variations of the b-spline coefficients combined with evaluation of the sensitivity of the registration metric with respect to the variations of the coefficients. It was evaluated based on patient data that was deformed based on a breathing model, where the ground truth of the deformation, and hence the actual true dose mapping error, is known.Results: The proposed approach has the potential to distinguish areas of the image where dose mapping is likely to be accurate from other areas of the same image, where a larger uncertainty must be expected.Conclusions: An approach to identify areas where dose mapping is likely to be inaccurate was developed and implemented. This method was tested for dose mapping, but it may be applied in context of other mapping tasks as well.
    Type of Publication: Journal article published
    PubMed ID: 22482640
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  • 8
    Keywords: radiotherapy ; radiation ; CELL-LINES ; mesothelioma ; radiosensitivity ; HETEROGENEITY ; COMPLICATION PROBABILITIES ; NORMAL-TISSUE ; TUMOR-CONTROL PROBABILITY ; DOSE-VOLUME
    Abstract: A method for quantitative visualization of the uncertainty in the predicted tumor control probability (TCP) and normal tissue complication probability (NTCP) in radiotherapy has been developed. Uncertainties of TCP and NTCP due to inter-individual variation of the underlying radiosensitivity parameters was simulated by sampling the prescribed dose from a uniform distribution and the radiosensitivity-parameters from a Gaussian distribution. The result is visualized as a scatter-plot superimposed to the population-based dose response curves using the prescribed dose as the common dosimetric variable. In addition, probability histograms are derived quantifying the probability of specific TCP- or NTCP-values for individual patients from the underlying population. The method is exemplified with a pleural mesothelioma case with the lung as organ at risk. A prescribed dose of 54 Gy together with radiosensitivity variations of 6% (tumor) and 10% (normal tissue) results in a TCP of 85% (range 68-94%, 90% confidence interval, CI) and an NTCP of 4% (range 3-6%, 90% CI), respectively. Increasing the radiosensitivity variation of the tumor to 15% and reducing the lung tolerance dose by 25% results in values of 84% (range 51-97%, 90% CI).for TCP and 9% (range 6-12%, 90% CI) for NTCP. Increasing the dose to 60 Gy leads to TCP- and NTCP-values of 93% (range 69-100%, 90% CI) and 12% (range 8-17%, 90% CI), respectively. The new method visualizes the uncertainty of TCP- and NTCP-values and hence of the therapeutic window. This can help the clinician to assess the treatment plan for the individual patient. (C) 2012 Associazione Italiana di Fisica Medica.
    Type of Publication: Journal article published
    PubMed ID: 23260766
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  • 9
    Keywords: CELLS ; radiotherapy ; SURVIVAL ; tumor ; CELL ; Germany ; neoplasms ; THERAPY ; TOXICITY ; FOLLOW-UP ; DISEASE ; TUMORS ; SURGERY ; radiation ; MRI ; PROGRESSION ; CONFORMAL RADIOTHERAPY ; EXPERIENCE ; RADIATION-THERAPY ; AGE ; EFFICACY ; REGION ; HEAD ; NECK ; local control ; ONCOLOGY ; overall survival ; radiation therapy ; MENINGIOMAS ; BONE ; SCAN ; INSTITUTION ; CASE SERIES
    Abstract: Background: Giant cell tumors are rare neoplasms, representing less than 5% of all bone tumors. The vast majority of giant cell tumors occurs in extremity sites and is treated by surgery alone. However, a small percentage occurs in pelvis, spine or skull bones, where complete resection is challenging. Radiation therapy seems to be an option in these patients, despite the lack of a generally accepted dose or fractionation concept. Here we present a series of five cases treated with high dose IMRT. Patients and Methods: From 2000 and 2006 a total of five patients with histologically proven benign giant cell tumors have been treated with IMRT in our institution. Two patients were male, three female, and median age was 30 years (range 20 - 60). The tumor was located in the sacral region in four and in the sphenoid sinus in one patient. All patients had measurable gross disease prior to radiotherapy with a median size of 9 cm. All patients were treated with IMRT to a median total dose of 64 Gy (range 57.6 Gy to 66 Gy) in conventional fractionation. Results: Median follow up was 46 months ranging from 30 to 107 months. Overall survival was 100%. One patient developed local disease progression three months after radiotherapy and needed extensive surgical salvage. The remaining four patients have been locally controlled, resulting in a local control rate of 80%. We found no substantial tumor shrinkage after radiotherapy but in two patients morphological signs of extensive tumor necrosis were present on MRI scans. Decline of pain and/or neurological symptoms were seen in all four locally controlled patients. The patient who needed surgical salvage showed markedly reduced pain but developed functional deficits of bladder, rectum and lower extremity due to surgery. No severe acute or late toxicities attributable to radiation therapy were observed so far. Conclusion: IMRT is a feasible option in giant cells tumors not amendable to complete surgical removal. In our case series local control was achieved in four out of five patients with marked symptom relief in the majority of cases. No severe toxicity was observed
    Type of Publication: Journal article published
    PubMed ID: 20187955
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  • 10
    Keywords: IRRADIATION ; Germany ; IN-VIVO ; SYSTEM ; RESOLUTION ; radiation ; PATIENT ; treatment ; RADIATION-THERAPY ; ENERGY ; LINE ; IONIZATION ; INTENSITY-MODULATED RADIOTHERAPY ; LINEAR-ACCELERATOR ; IMRT ; in vivo ; TRANSMISSION ; CLINICAL IMPLEMENTATION ; DIODE DOSIMETRY ; ROUTINE QUALITY-ASSURANCE
    Abstract: Permanent in vivo verification of IMRT photon beam profiles by a radiation detector with spatial resolution, positioned on the radiation entrance side of the patient, has not been clinically available so far. In this work we present the DAVID system, which is able to perform this quality assurance measurement while the patient is treated. The DAVID system is a flat, multi-wire transmission-type ionization chamber, placed in the accessory holder of the linear accelerator and constructed from translucent materials in order not to interfere with the light field. Each detection wire of the chamber is positioned exactly in the projection line of a MLC leaf pair, and the signal of each wire is proportional to the line integral of the ionization density along this wire. Thereby, each measurement channel essentially presents the line integral of the ionization density over the opening width of the associated leaf pair. The sum of all wire signals is a measure of the dose-area product of the transmitted photon beam and of the total radiant energy administered to the patient. After the dosimetric verification of an IMRT plan, the values measured by the DAVID system are stored as reference values. During daily treatment the signals are re-measured and compared to the reference values. A warning is output if there is a deviation beyond a threshold. The error detection capability is a leaf position error of less than I mm for an isocentric I cm x I cm field, and of I mm for an isocentric 20 cm x 20 cm field
    Type of Publication: Journal article published
    PubMed ID: 16481690
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