Biomedical subjects

R Bendl

Publications and source records attributed to R Bendl.

9 recordsLinked to original sources

PubMed2006

An enhanced block matching algorithm for fast elastic registration in adaptive radiotherapy.

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 5 min, 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.

Algorithms↗

PubMed2006

Kilovoltage CT using a linac-CT scanner combination.

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.

Humans↗

PubMed2005

An optimized workflow for the integration of biological information into radiotherapy planning: experiences with T1w DCE-MRI.

Planning of radiotherapy is often difficult due to restrictions on morphological images. New imaging techniques enable the integration of biological information into treatment planning and help to improve the detection of vital and aggressive tumour areas. This might improve clinical outcome. However, nowadays morphological data sets are still the gold standard in the planning of radiotherapy. In this paper, we introduce an in-house software platform enabling us to combine images from different imaging modalities yielding biological and morphological information in a workflow driven approach. This is demonstrated for the combination of morphological CT, MRI, functional DCE-MRI and PET data. Data of patients with a tumour of the prostate and with a meningioma were examined with DCE-MRI by applying pharmacokinetic two-compartment models for post-processing. The results were compared with the clinical plans for radiation therapy. Generated parameter maps give additional information about tumour spread, which can be incorporated in the definition of safety margins.

Algorithms↗

PubMed2001

Real-time dose calculation and visualization for the proton therapy of ocular tumours.

A new real-time dose calculation and visualization was developed as part of the new 3D treatment planning tool OCTOPUS for proton therapy of ocular tumours within a national research project together with the Hahn-Meitner Institut Berlin. The implementation resolves the common separation between parameter definition, dose calculation and evaluation and allows a direct examination of the expected dose distribution while adjusting the treatment parameters. The new tool allows the therapist to move the desired dose distribution under visual control in 3D to the appropriate place. The visualization of the resulting dose distribution as a 3D surface model, on any 2D slice or on the surface of specified ocular structures is done automatically when adapting parameters during the planning process. In addition, approximate dose volume histograms may be calculated with little extra time. The dose distribution is calculated and visualized in 200 ms with an accuracy of 6% for the 3D isodose surfaces and 8% for other objects. This paper discusses the advantages and limitations of this new approach.

Algorithms↗

PubMed1998

Limitations for three-dimensional ultrasound imaging through a bore-hole trepanation.

The intraoperative shift of neuroanatomical landmarks that serve as reference points is an unsolved problem in current neuronavigation. Monitoring the position of these landmarks requires repeated intraoperative imaging. We analyzed the effectiveness of a 3-D ultrasound system for imaging through a bore-hole trepanation. A tissue-mimicking ultrasound phantom and plastic pads with bore-holes were utilized for in vitro tests of the system. Reducing the diameter of the simulated bore-hole decreased the image quality and reduced the field of view. The multiple plane mode of the 3-D ultrasound system allows reconstruction of images in arbitrary imaging planes on the basis of intraoperatively acquired 3-D datasets. Selecting planes that are coplanar with preoperative MRI scans, we were able to identify neuroanatomical landmarks in the reconstructed ultrasound images. Repeated 3-D ultrasound during a procedure might, therefore, allow recognition of a shift of these landmarks.

Artifacts↗

PubMed1997

Inverse radiotherapy planning for a concave-convex PTV in cervical and upper mediastinal regions. Simulation of radiotherapy using an Alderson-RANDO phantom. Planning target volume.

AIM: Three-dimensional inverse treatment planning with modulated beams was applied for dosimetric optimization of a lengthy (22 cm) and complex (concave-convex) shaped planning target volume (PTV) in the cervical and upper mediastinal regions. MATERIAL AND METHOD: The planning was done for 9 coplanar beams spaced evenly at 40 intervals. Properties of 15 MV photons from a linear accelerator were simulated. The optimization of the fluence modulation profiles for each beam was based on a definition of the desired/permitted relative dose levels in the PTV and organs at risk, and a definition of the strengths of the constraints to achieve these objectives. RESULTS: An adequate dose delivery to the PTV and protection of the spinal cord are completely achievable. The dose delivered to the lungs is clinically acceptable with respect to the risk of radiation-induced pneumonitis. For reasons of physics, no further decrease in the radiation burden on the lungs can be attained with X-rays without compromising the PTV coverage. The radiation burden on some critical part of normal tissues was effectively reduced by application of a dummy organ at risk. CONCLUSION: The inverse planning is an effective method for conformal radiotherapy of large tumors as well. However, the power of the technique is insufficient when the tolerance dose of the neighbouring normal tissue is too low and its volume effect is high. Although requiring further operator interactions, introduction of dummy organs at risk may be of help in reducing the radiation burden on normal tissues.

Body Burden↗

PubMed1996

[Image-guided therapy planning for interventional stereotactic therapy of brain tumors].

A treatment planning system for stereotactical neurosurgery has been developed. A modular system has been designed which is readily extendable. Different modalities of tomography (CT, MRI) can be correlated and presented simultaneously in transverse, frontal and sagittal reconstructions. The volumes of interest are segmented with respect to the different modalities, and the positions of the catheters are defined. The calculation of dose must be adapted to the physical requirements of the therapy and is designed as an independent process. The calculated data are shown in various presentations. The treatment planning system is applied to intratumoral chemotherapy. The drug is encapsulated in small carriers for prolonged release and injected via catheters directly into the tumor interstitium, bypassing the blood-brain barrier. The dose is calculated using the time-dependent, three-dimensional finite elements method. To achieve homogeneous temporal and spatial drug distribution it is necessary to use a great number of catheters due to the limited diffusion of drug, which is not practical in neurosurgery. Therefore this therapy concept is useful for small volumes only. Interstitial hyperthermia and brachytherapy, in contrast to intratumoral chemotherapy, show successful clinical results.

Antineoplastic Agents↗

PubMed1995

[Computerized procedures in 3-dimensional radiotherapy planning].

UNLABELLED: The aim of 3D radiotherapy treatment planning is to match the dose as closely as possible to the target volume, thus avoiding side effects in healthy tissue and radiosensitive organs at risk. A virtual radiotherapy simulator designed for the definition of treatment parameters and the analysis of precalculated dose distributions enables iterative optimization of treatment plans. METHODS: VOXELPLAN is a software package for 3D radiotherapy treatment planning developed at the German Cancer Research Center; it consists of user interfaces for image segmentation, virtual therapy simulation, dose calculation, plan evaluation and patient documentation. It is written in C and FORTRAN and runs on VAXstation 4000, IBM RS/6000 and DEC ALPHA hardware. RESULTS: Since 1990 a pilot installation of VOXELPLAN has been applied in clinical routine at the Center and at the University Clinic for Radiology, Heidelberg. Treatment for more than 1500 patients has been planned and carried out using the system, proving its technical and organizational applicability. CONCLUSIONS: We expect better acceptance and further dissemination of the techniques described, conformation therapy as well as (after its technical realization) inverse planning, from continuous optimization of the planning process.

Head and Neck Neoplasms↗

PubMedDate not supplied

Technical aspects of internet-based knowledge presentation in radiotherapy.

Three-dimensional radiotherapy planning is a complex and time-consuming optimization process which requires much experience. To simplify and to speed up the process of treatment planning as well as to exchange experience and therapeutic knowledge, the department of Medical Physics at the German Cancer Research Centre (DKFZ) in Heidelberg is developing an Internet-based 3D Radiotherapy planning and Information System (IRIS). IRIS designed internet-based client-server application, implemented using Java, CORBA and PVM. The concept of IRIS combines the functionality of an interactive tutorial with a discussion forum, teleconferencing tool and an atlas of dose distributions. Furthermore an integral knowledge-based system provides automatically generated, preoptimized treatment plans. This paper explains the technical design of the system and gives an overview of experiences gained by the technical realization of a first prototype using currently available internet technology. The prototype is currently running for testing in the intranet of DKFZ.

Artificial Intelligence↗