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G H Hartmann

Publications and source records attributed to G H Hartmann.

10 recordsLinked to original sources
PubMed1992

The influence of mineralising radionecrosis on the dose distribution in interstitial radiation therapy of brain tumours.

The influences of radionecroses arising during interstitial radiation of brain tumours with 125I, 192Ir or 198Au on dose distribution was investigated using Monte Carlo methods. The necroses have a higher density than normal tissue due to radiation-induced changes in tissue composition as well as mineral deposits. They can have a diameter of up to 1 cm around the single seeds. The higher density and changed chemical composition compared to homogeneous normal tissue leads to increased absorption of radiation around the necroses which results in a lower dose rate in the surrounding tissue. It is shown that the formation of necroses during treatment with higher energy radiation such as 192Ir (340 keV) or 198Au (400 keV) may be neglected during therapy planning as the dose rate is affected by less than 2%. If low energy radiation, e.g. 125I (28 keV) is used, the dose rate can be reduced by more than 30%. In this case the influence of the necroses on dose distribution, at least for permanent 125I implantation, may not be negligible.

Animals↗
PubMed1992

Tissue maximum ratios (and other parameters) of small circular 4, 6, 10, 15 and 24 MV x-ray beams for radiosurgery.

Small, circular, x-ray beams are commonly used for radiosurgery applications. Dosimetric characteristics of 4, 6, 10, 15 and 24 MV circular x-ray beams ranging in size from 10 to 40 mm are reported. These characteristics include the measurement of TMR, beam profiles and relative output factors. Measurements of these parameters were performed in a solid water phantom using film, a small diode, small parallel-plate and cylindrical ionization chambers and TLD. Comparison of relative dose measurements of small, circular beams performed using these detectors showed that the small diode, film and TLD results consistently agreed for circular beams as small as 10 mm diameter. Beam profiles were measured using film dosimetry. Comparison of TMR values of a 10 mm diameter beam measured using film and a small parallel-plate ionization chamber showed no significant differences. Tertiary collimators designed with tapered, divergence-matching holes, and straight-drilled holes have been used for radiosurgery applications. Measurement of beam penumbra produced with either of these types of tertiary collimators showed minimal differences between them.

Humans↗
PubMed1991

Stereotactic target point verification of an X ray and CT localizer.

Stereotactic radiosurgery with a linear accelerator requires the accurate determination of a target volume and an accurate match of the therapeutic radiation dose distribution to the target volume. X ray and CT localizers have been described that are used to define the target volume or target point from angiographic or CT data. To verify the accuracy of these localizers, measurements were made with a target point simulator and an anthropomorphic head phantom. The accuracy of determining a known, high contrast, target point with these localizers was found to be a maximum of +/- 0.5 mm and +/- 1.0 mm for the X ray and CT localizer, respectively. A technique using portal X rays taken with a linear accelerator to verify the target point is also described.

Radiotherapy↗
PubMed1990

The medical heavy ion therapy project at the Gesellschaft für Schwerionenforschung facility in Darmstadt.

It could be demonstrated that local tumor control is considerably improved by radiation therapy with charged particles (protons or heavier ions). The advantages of heavy ion therapy compared to conventional photon therapy techniques are due to the better physical dose distributions achievable and the radiobiological characteristics of heavy ions. However, because of the expense and complexity of heavy ion therapy it is only carried out at a few facilities throughout the world. The Radiologische Universitätsklinik (Radiological University Hospital) and the Deutsches Krebsforschungszentrum (German Cancer Research Centre, DKFZ) in Heidelberg, in collaboration with the Gesellschaft für Schwerionenforschung (Laboratory for Heavy Ion, GSI) in Darmstadt, have developed a concept to use the new heavy ion synchrotron (Schwerionen-Synchroton SIS) in Darmstadt for medical-clinical irradiations. Due to the high flexibility of the SIS accelerator the medical program can be performed in addition to the planned physical experiments with minor interference only. The close geographical proximity of the three institutes involved and the accelerator which will be completed by the end of 1989 provide the unique opportunity to carry out relevant clinical, medical-physical, physical-technical, and radiobiological research in a relatively short time and, compared to similar projects in other countries, at low cost.

Costs and Cost Analysis↗
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↗
PubMed1987

In vitro model for the response to irradiation of different types of human intracranial tumours.

Twenty-seven human low and high grade gliomas and five meningiomas were cultured in vitro as tumour tissue and/or tumour cells. Cell survival or growth was taken as a measure of radiation response. Astrocytomas II-III and glioblastomas manifested individual patterns of radiosensitivity, ranging from 10 to 90 Gy. Meningiomas did not react. Our findings are consistent with the differences in radiosensitivity of human gliomas experienced clinically and corroborate the validity of the in vitro model.

Brain Neoplasms↗
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↗
PubMed1985

Cerebral radiation surgery using moving field irradiation at a linear accelerator facility.

A modified irradiation technique at a linear accelerator facility for radiation surgery within the brain is described consisting of several moving field irradiations in non-coplanar planes. Using collimated narrow beams, a localization system and special computer programs for precise patient positioning, a high concentration of dose within small, well circumscribed volumes is obtained. Resulting dose distributions were studied experimentally and by calculations. A simple algorithm for treatment planning was developed and based on CT images. Radiation surgery within the brain is now technically feasible at our linear accelerator. Seventeen patients have now been treated.

Brain↗
PubMedDate not supplied

Three dimensional image correlation of CT, MR, and PET studies in radiotherapy treatment planning of brain tumors.

A treatment planning system for stereotactic convergent beam irradiation of deeply localized brain tumors is reported. The treatment technique consists of several moving field irradiations in noncoplanar planes at a linear accelerator facility. Using collimated narrow beams, a high concentration of dose within small volumes with a dose gradient of 10-15%/mm was obtained. The dose calculation was based on geometrical information of multiplanar CT or magnetic resonance (MR) imaging data. The patient's head was fixed in a stereotactic localization system, which is usable at CT, MR, and positron emission tomography (PET) installations. Special computer programs for correction of the geometrical MR distortions allowed a precise correlation of the different imaging modalities. The therapist can use combinations of CT, MR, and PET data for defining target volume. For instance, the superior soft tissue contrast of MR coupled with the metabolic features of PET may be a useful addition in the radiation treatment planning process. Furthermore, other features such as calculated dose distribution to critical structures can also be transferred from one set of imaging data to another and can be displayed as three-dimensional shaded structures.

Brain↗