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O Pastyr

Publications and source records attributed to O Pastyr.

At least 19 recordsLinked to original sources
PubMed1998

[Stereotactic conforming irradiation of choroid metastases].

UNLABELLED: The aim of our study was to develop noninvasive stereotactic radiotherapy for patients with choroidal metastases. METHODS: The head of the patient was immobilized by an individual cast mask. The target volume and adjacent critical structures were three-dimensionally segmented based on ophthalmological findings and MRI. The beam angles were optimized by a beam's eye view technique with a micro-multileaf collimator. We use a linear accelerator with 6-MeV photons. A patient was treated in a phase I/II trial with a single dose of 22.5 Gy. RESULTS: The accuracy of stereotactic positioning of the eye was 0.8 mm. The dose gradients were 15% mm. It was possible to spare the lens and the lacrimal gland in all cases. The treatment with four to six fields took 35-50 min and was tolerated without acute complications. CONCLUSIONS: We introduce a new method to treat choroid metastases by stereotactic radiotherapy. This method allows to concentrate the dose to the target and to spare adjacent critical structures. One of the advantages of this noninvasive treatment is the short treatment time. The clinical role of this method has to be evaluated based on long-term results of tumor control and visual outcome in these patients.

Adenocarcinoma↗
PubMed1997

Intraoperative diagnostic and interventional magnetic resonance imaging in neurosurgery.

OBJECTIVE: The benefits of intraoperative magnetic resonance (MR) imaging for diagnostic and therapeutic measures are as follows: 1) intraoperative update of data sets for navigational systems, 2) intraoperative resection control of brain tumors, and 3) frameless and frame-based on-line MR-guided interventions. The concept of an intraoperative MR scanner in the sterile environment of operating theater is presented, and its advantages, disadvantages, and limitations are discussed. METHODS: A 0.2-tesla magnet (Magnetom Open; Siemens AG, Erlangen, Germany) inside a radiofrequency cabin with a radiofrequency-shielded sliding door was installed adjacent to one of the operating theaters. A specially designed patient transport system carried the patient in a fixed position on an air cushion to the scanner and back to the surgeon. RESULTS: In a series of 27 patients, intraoperative resection control was performed in 13 cases, with intraoperative reregistration in 4 cases. Biopsies, cyst aspirations, and catheter placements (mainly frameless) were performed under direct MR visualization with fast image sequences. The MR-compatible equipment and the patient transport system are safe and reliable. CONCLUSION: Intraoperative MR imaging is a safe and successful tool for surgical resection control and is clearly superior to computed tomography. Intraoperative acquisition of data sets eliminates the problem of brain shift in conventional navigational systems. Finally, on-line MR-guided interventional procedures can be performed easily with this setting. As with all MR systems, individual testing with phantoms, application of correction programs, and determination of the optimal amount of contrast media are absolute prerequisites to guarantee patient safety and surgical success.

Adult↗
PubMed1994

Photogrammetric accuracy measurements of head holder systems used for fractionated radiotherapy.

PURPOSE: We describe how stereo photogrammetry can be used to determine immobilization and repositioning accuracies of head holder systems used for fractionated radiotherapy of intracranial lesions. METHODS AND MATERIALS: The apparatus consists of two video cameras controlled by a personal computer and a bite block based landmark system. Position and spatial orientation of the landmarks are monitored by the cameras and processed for the real-time calculation of a target point's actual position relative to its initializing position. The target's position is assumed to be invariant with respect to the landmark system. We performed two series of 30 correlated head motion measurements on two test persons. One of the series was done with a thermoplastic device, the other one with a cast device developed for stereotactic treatment at the German Cancer Research Center. Immobilization and repositioning accuracies were determined with respect to a target point situated near the base of the skull. The repositioning accuracies were described in terms of the distributions of the mean displacements of the single motion measurements. RESULTS: Movements of the target in the order of 0.05 mm caused by breathing could be detected with a maximum resolution in time of 12 ms. The data derived from the investigation of the two test persons indicated similar immobilization accuracies for the two devices, but the repositioning errors were larger for the thermoplastic device than for the cast device. Apart from this, we found that for the thermoplastic mask the lateral repositioning error depended on the order in which the mask was closed. CONCLUSION: The photogrammetric apparatus is a versatile tool for accuracy measurements of head holder devices used for fractionated radiotherapy.

Head and Neck Neoplasms↗
PubMed1994

Linac radiosurgery in brain metastases.

Brain metastases are usually well-circumscribed and more or less spherical lesions. These conditions meet the criteria for radiosurgery (RS). A pilot study initiated by our group in 1983, demonstrated the effectiveness of Linac-RS in the treatment of solitary brain metastases with low radiosensitivity. A second trial including patients with 1-3 metastases started in 1990. By April 1993, 46 patients had been treated in this series. The radiation doses delivered to the tumour margin ranged from 10 to 25 Gy, and were chosen with respect to size, number and location of the tumours or previous whole brain radiotherapy (WBRT), decreasing mainly with increasing tumour volumes. 34/46 patients had a follow-up of more than 12 weeks. In 7/46 patients the disease progressed rapidly during the first weeks after RS and follow-up examinations were not performed. 5/46 patients had a follow-up of less than 6 weeks and follow-up CT/MR-examinations were not available. 14/46 patients received WBRT before RS. The regularly performed follow-up examinations (clinical status, CT-/MR-examinations in 6 or 12 weekly intervals) revealed tumour progression in 5/34 patients. Permanent cessation of the growth (11/34), tumour shrinkage (18/34) and decrease of surrounding oedema together with clinical amelioration have been observed a few weeks after radiosurgery. The median follow-up was 50 weeks. 14/46 patients died due to generalized progression of their disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Linac-accelerator-radiosurgery.

A survey is given of the actual possibilities and limitations of the use of linear accelerators (Linac radiosurgery systems) for intra = cranial radiosurgery. Depending on the collimator size, spherical fields from 5-54 mm in diameter can be irradiated with dose gradients from 10% (large fields) to 20% (small fields) per millimeter distance between surface and treatment volume. This is comparable to the possibilities of Gamma-Knife and Proton-irradiation. Optimal mechanical adjustment of gantry and linac table are necessary for the required stability of the isocenter. Mechanical inaccuracy should be smaller than 0.8 mm. Advanced computerized 3D-treatment planning systems are indispensable prerequisites for accurate treatment and use of the flexibility of the linac system. Future developments are outlined.

Brain↗
PubMed1993

Interstitial irradiation of cerebral gliomas with stereotactically implanted iodine-125 seeds.

Ninety-seven consecutive patients with primarily inoperable or only partially resectable gliomas have been analysed retrospectively. Mean tumour surface doses of 70 Gy (low grade gliomas) and 56 Gy (high grade gliomas) have been applied with stereotactically implanted Iodine-125 seeds at low dose rates. Patients with a glioma grade III or grade IV and permanent seed implantation additionally received a fractionated external beam irradiation. With mean follow-up times of 55.8 months (glioma grade I), 51 months (glioma grade II) and 59.6 months (glioma grade III) the estimated mean survival probabilities are 105 months, 102 months and 65.7 months respectively. In the glioma grade IV group the estimated mean survival time has been 15.6 months after continuous interstitial irradiation (response rate: 36%). Temporary interstitial irradiation in cases with a glioma grade IV (dose rate: 2.1 Gy/day) caused initial tumour shrinkage in 77%. Neurological deficits following radiation induced vasogenic oedema were reversible in 2 patients and irreversible in another 2 patients. 6 years after the Iodine-125 implantation and continuous interstitial irradiation 1 patient developed a severe localised radiation necrosis.

Adolescent↗
PubMed1993

CT-guided and computer assisted stereotactic biopsy. Technique, results, indications.

On the base of a stereotactic device originally described by Riechert and Mundinger a three-dimensional localization and treatment planning system for CT-guided computer assisted stereotactic procedures has been developed. The experience with 338 patients, in which image guided stereotaxy has been used for the assessment of various intracerebral lesions, is presented. In 54 of these patients the cannula was introduced with a 20 MHz Doppler-probe positioned at the tip of the needle. A comparison of tissue specimens taken stereotactically with tissue material after tumour resection and/or autopsy was performed in 35 patients. The accuracy of the histological diagnosis was 88%. Bleeding as a complication due to the stereotactic intervention occurred in 8 patients (2.4%). Two of these patients had a fatal outcome (mortality: 0.6%). The morbidity (transient and permanent deterioration of the clinical status) was 1.2%.

Adolescent↗
PubMed1993

Interstitial irradiation of a large, low grade ependymoma with stereotactically implanted iodine-125 seeds. Case report.

In this case report a patient with a large intraventricular benign ependymoma is presented. The tumour was treated with stereotactically implanted Iodine-125 seeds and interstitial irradiation. Extension (diameter: 6.5 cm) and volume (112.5 ml) of the lesion caused the application of an unusually low dose (tumour surface dose: 40 Gy). The tumour shrank significantly within a few weeks. Follow-up at nearly 5 years shows the patient to be tumour free.

Adult↗
PubMed1993

Stereotactically guided fractionated radiotherapy: technical aspects.

A system for high precision radiotherapy in the head and neck region has been developed. The components of the system are a head mask connected to a stereotactic frame, a localization unit that can be used during CT- and MR-imaging and a stereotactic target positioner. Conformal precision radiotherapy is planned with a new treatment planning system (Voxelplan-Heidelberg). Three different multi-leaf collimator systems are used. An evaluation of the precision and accuracy of the head fixation system, which was performed with a photogrammetry system, is presented.

Head↗
PubMed1992

Computer systems and mechanical tools for stereotactically guided conformation therapy with linear accelerators.

An integrated system for fractionated, stereotactically guided conformation radiotherapy has been developed. The system components are a stereotactic fixation system that can be used each treatment day, a localization, and positioning unit that can be used during x-ray computer tomography, magnetic resonance imaging, positron emission tomography, and radiographical examinations as well as for treatment. Conformal precision radiotherapy is planned with a new three-dimensional treatment planning system (Voxel-Plan-Heidelberg) which comprises, among others options, a three-dimensional image correlation procedure as well as routines for the calculation of coplanar and non-coplanar irradiations with irregularly shaped fields. Two different multi-leaf collimators have been designed for precision radiotherapy in the head and neck region. A manual multi-leaf collimator is used for irradiations with stationary beams or for moving beam treatments with invariable irregularly shaped fields. This collimator system is now being used for patient treatments. The design of a computer controlled multi-leaf collimator unit for multiple fixed field irradiation techniques is discussed. All system components are aimed at conforming dose distributions for fractionated radiotherapy treatments to the target to improve sparing of adjacent normal tissues, and at achieving a sufficient geometrical accuracy in the dose application.

Computer Systems↗
PubMed1991

Modification of a three-dimensional treatment planning system for the use of multi-leaf collimators in conformation radiotherapy.

The multi-leaf collimator of the DKFZ is designed as a low cost add-on device for conventional linear accelerators for radiotherapy. The technical specification of the computer controlled collimator is described briefly. A major limitation in the use of the wide capabilities of multi-leaf collimators in the clinic is still an appropriate treatment planning system. This paper describes treatment planning and dose calculation techniques for multi-leaf collimators and shows examples where the capabilities of the collimator are used extensively.

Dose-Response Relationship, Radiation↗
PubMed1991

A new applicator, positionable to the center of tracheobronchial lumen for HDR-IR-192-afterloading of tracheobronchial tumors.

A new bronchial applicator for afterloading irradiation is introduced which can be positioned to the center of the tracheobronchial lumen. The central position in the lumen leads to a clear improvement of dose distribution. The applicator is built on the principle of a coaxial tube. Parts of the outer cover can be expanded to baskets and effect a distance of the radiation source from the bronchial mucosa or tumor surface, and at the same time, expend a relief of extreme contact doses. No obstruction of the respiratory system through the positioning device will be caused. The positionable bronchial applicator seems to be suitable for reducing complications caused through high contact doses and irregular dose distributions and may be able to improve the results of endoluminal radiotherapy.

Brachytherapy↗
PubMed1991

Radiosurgical treatment of cerebral metastases. Method, indications and results.

Stereotactically guided single-dose irradiation of brain metastases with low radiosensitivity has been performed in a series of 30 patients. Clinical symptoms improved in 18 of 27 evaluated patients and remained stable in another 7. Tumour regression was achieved in 13 of 22 patients, and arrest of tumour growth in 7 other patients. The treatment was usually well tolerated. The incidence of side effects was low. Thus, radiosurgery seems to be a valuable alternative to microsurgical extirpation of solitary brain metastases with low radiosensitivity.

Adult↗
PubMed1990

[A simple method for positioning and fixing the extremities during the radiotherapy of soft-tissue sarcomas].

The exact and reproducible radiotherapy of malignant tumours in the extremities is aided by reliable positioning of the involved limb. In our department individually-formed casts and circular fix up made of two-component polyurethane foam (NEOFRAKT, supplied by Schumacher, Krefeld, FRG) are used. These allow the maintenance of any bending, stretching and torsional positions. The fields to be applied are cut out of the casts, thus preventing any influence on the depth dose of the radiation involved.

Arm↗
PubMed1989

Stereotactically guided convergent beam irradiation with a linear accelerator: localization-technique.

A stereotactic convergent beam irradiation technique using a linear accelerator has been developed in order to precisely apply single high doses of up to 50 gray and more to brain lesions (radiosurgery). Accurate positioning of the patient and the target point of irradiation is an absolute requirement for this method. The stereotactic localization system developed for this purpose is described.

Humans↗
PubMed1988

Treatment planning for conformation therapy using a multi-leaf collimator.

In high energy photon therapy an optimum dose distribution is achieved with an irradiation from several directions, thus adapting the field shape to the target volume. Some methods of irradiation planning using these techniques are presented. The result of such a treatment planning is demonstrated.

Humans↗
PubMed1987

Stereotactic percutaneous single dose irradiation of brain metastases with a linear accelerator.

The effectivity of stereotactic percutaneous single dose irradiations in the treatment of solitary brain metastases has been assessed in a series of 12 consecutive patients. Only radioresistant deeply localized metastases have been treated. Photon-irradiation was carried out with the convergent beam technique using stereotactic localization methods, in a linear accelerator facility. In 11 of the 12 patients no side effects occurred. The first 7 patients, who could be observed 3 months or longer, have been studied in detail. In each of these cases single dose irradiation with 20-30 Gy yielded arrest of tumor growth. In one case a marked decrease in contrast enhancement and in four cases shrinkage of the metastasis as well as a marked decrease of the edema occurred. In every patient a marked, sometimes dramatic improvement of the clinical condition was achieved, beginning a few days after irradiation. Stereotactic radiosurgery is a valuable tool in the treatment of inoperable, radioresistant brain metastases, the major advantage being high efficacy and smoothness of the procedure, as well as extremely short hospitalization times (2-3 days).

Adult↗