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J Debus

Publications and source records attributed to J Debus.

At least 127 records · Page 7Linked to original sources
PubMed1999

High-resolution MR venography of cerebral arteriovenous malformations.

The purpose of this study was to evaluate the diagnostic potential of a high-resolution magnetic resonance (MR) venography technique in patients with cerebral arteriovenous malformations (AVMs). A high-resolution 3D gradient echo sequence was used with a long echo time TE to obtain venous information down to sub-pixel sized vessel diameters of several hundred microns. The method is based on the paramagnetic property of deoxyhemoglobin, and the resulting developing phase difference between veins and brain parenchyma at long echo times which leads to signal cancellation. The reconstructed venograms were compared with time-of-flight (TOF)-MR angiography using qualitative and quantitative criteria with the conventional digital subtraction angiography serving as the reference gold standard. In 17 patients with angiographically proven cerebral AVMs, the method indicates its potential in clinical applications. Venography was able to detect all AVMs whereas TOF-MRA failed in three patients. In the delineation of venous drainage patterns MR venography was superior to TOF-MRA, however, the method failed in the detection of about half of the main feeding arteries, as expected. Due to susceptibility artifacts at air/tissue boundaries and interference with paramagnetic hemosiderin, venography was limited with respect to the delineation of the exact nidus sizes and shapes in ten patients with AVMs located close to the skull base or having suffered from previous bleeding. Although the visualization of draining veins represents an important prerequisite in the surgical and radiosurgical treatment planning of cerebral AVMs, application of high resolution MR venography may be limited in the diagnostic work-up in some of these patients. On the other hand, it may be of special importance in the early detection and assessment of small AVMs that are difficult to diagnose with other MR methods.

Adolescent↗
PubMed1999

Control of cavitation activity by different shockwave pulsing regimes.

The aim of the study was to control the number of inertial cavitation bubbles in the focal area of an electromagnetic lithotripter in water independently of peak intensity, averaged intensity or pressure waveform. To achieve this, the shockwave pulses were applied in double pulse sequences, which were administered at a fixed pulse repetition frequency (PRF) of 0.33 Hz. The two pulses of a double pulse were separated by a variable short pulse separation time (PST) ranging from 200 micros to 1500 ms. The number and size of the cavitation bubbles were monitored by scattered laser light and stroboscopic photographs. We found that the number of inertial cavitation bubbles as a measure of cavitation dose was substantially influenced by variation of the PST, while the pressure pulse waveform, averaged acoustic intensity and bubble size were kept constant. The second pulse of each double pulse generated more cavitation bubbles than the first. At 14 kV capacitor voltage, the total number of cavitation bubbles generated by the double pulses increased with shorter PST down to approximately 400 micros, the cavitation lifespan. The results can be explained by cavitation nuclei generated by the violently imploding inertial cavitation bubbles. This method of pulse administration and cavitation monitoring could be useful to establish a cavitation dose-effect relationship independently of other acoustic parameters.

Dose-Response Relationship, Radiation↗
PubMed1999

Digitally reconstructed radiographs from abdominal CT scans as a new tool for radiotherapy planning.

OBJECTIVE: Abdominal extended field radiotherapy requires exact field shaping. Conventional treatment planning is difficult to adapt to individual anatomy, whereas three-dimensional planning is time-consuming. The authors introduce a method with digitally reconstructed radiographs of spiral CT data to facilitate radiotherapy planning. METHODS: Twenty-two patients underwent imaging with a standardized CT protocol, and digitally reconstructed radiographs were calculated in central beam projection using a maximum intensity projection algorithm (MIP-DRR). For comparison, the expected error from parallel projection was calculated depending on object thickness and field length. RESULTS: The contrast-enhanced protocol used in spiral CT produces a good rendition of all relevant structures. The resulting MIP images have a geometry identical to standard simulation films and to the linear accelerator, whereas standard MIPs with parallel projection show significant distortion compared to the treatment process. CONCLUSIONS: Because of the integration of the geometry of the radiotherapy treatment, the described central beam projection method might be used as a new tool for abdominal radiotherapy planning. The CT protocol offers sufficient contrast enhancement in all relevant structures and provides all necessary anatomic information for individual beam shaping.

Adult↗
PubMed1999

Patient position verification using CT images.

The use of ions in the radiotherapy of cancer patients requires an accurate patient positioning in order to exploit its potential benefits. Using CT images as the basis for the setup verification offers the advantage of a high in-plane resolution in combination with a geometrically accurate, volumetric information. Before each fraction a single CT slice is acquired at the isocenter level after the positioning procedure. This single slice is registered to the planning CT cube using automated image registration algorithms. Thus any erreonous translation or rotation can be detected and quantified. The registration process involves the interpolation of the volumetric data, the calculation of an energy function, and the minimization of this energy function. Several data interpolation functions as well as minimization algorithms were compared. CT studies with a head phantom were performed in which defined translations and rotations were simulated by moving a motor-driven treatment chair. Different slice thicknesses and anatomical sites were studied to investigate their potential influence on the registration accuracy. The accuracy of the registration was found to be a fraction of a voxel size for suitable combinations of algorithms (typically better than 0.16 mm/deg). A significant dependancy of the registration accuracy on the CT slice thickness and the anatomical site was found (the accuracy ranges from 0.05 mm/deg to 0.16 mm/deg depending on the site). The calculation time is dependant on the used algorithms and the magnitude of the setup error. For the standard combination of algorithms as proposed by the authors (Downhill Simplex minimization with Trilinear interpolation) the typical calculation time is about 20 s for a Sun UltraSPARC processor. Taking into account the mechanical accuracy of the setup device (motor-driven chair) the registration of CT images is thus a useful tool for detecting and quantifying any significant error in the patient position.

Algorithms↗
PubMed1999

Cerebral gliomas and metastases: assessment with contrast-enhanced fast fluid-attenuated inversion-recovery MR imaging.

The effect of contrast material on fast fluid-attenuated inversion-recovery (FLAIR) magnetic resonance images was evaluated for 16 patients with enhancing gliomas and 12 patients with cerebral metastases. Because of a marked T1 effect, fast FLAIR imaging provided a marked contrast enhancement, resulting in the highest tumor-to-background contrast ratio compared with standard imaging techniques.

Adult↗
PubMed1999

Delayed vascular injury after single high-dose irradiation in the rat brain: histologic immunohistochemical, and angiographic studies.

PURPOSE: To investigate structural and functional changes in rats after focal brain irradiation by using histologic, immunohistochemical, and angiographic methods. MATERIALS AND METHODS: Sixty rats were irradiated stereotactically with photons from a 15-MeV linear accelerator. Two collimators and single doses ranging from 20 to 100 Gy were used to treat stereotactically defined areas of 3.7- and 4.7-mm cross section (80% isodose) in the right frontal lobe. The dose-response relationship for the end-point necrosis at 19 months revealed a mean tolerance dose (D50) of 34.2 Gy (standard errors: +4.1, -3.7 Gy). Histologic, immunohistochemical, and angiographic examinations were performed to evaluate delayed radiation effects. RESULTS: All animals irradiated with 100 Gy developed radiation necrosis after 9 months. Microangiography and immunohistochemical fluorescence staining of the endothelial cells revealed dose-dependent vascular dilatation and rarefaction. Animals irradiated with 20-50 Gy showed no morphologic changes after 9 months. With irradiation of 30-50 Gy, histologic vascular changes that increased with dose were found after 19 months. At that time, no changes were detected after irradiation with 20 Gy with both field sizes and after irradiation with 30 Gy and the 2-mm collimator. Radiation-induced functional disturbances of the brain vasculature could be demonstrated by extravasation of contrast medium by using a microangiographic technique. CONCLUSION: The observed effect had a definite dependence on dose, volume, and time after treatment.

Animals↗
PubMed1998

Assessment of neuropsychological changes in patients with arteriovenous malformation (AVM) after radiosurgery.

PURPOSE: The purpose of this study was to investigate neuropsychological effects of radiosurgery in patients with cerebral arteriovenous malformation (AVM), with special focus on attention and memory. This report describes the study setup and presents the first results during a follow-up of up to 1 year. MATERIALS AND METHODS: Seventy-nine patients were studied before, acutely after radiosurgery, and during the regular follow-up (subacute phase: Weeks 6-12, chronic phase: Months 6-12). Radiosurgery was performed using a modified linear accelerator (minimum doses to the target volume: 15-22 Gy, median 20 Gy). Estimated whole brain dose was 0.5 to 2 Gy. Neuropsychological testing included assessment of general intelligence (Wechsler Adult Intelligence Scale), attention (modified Trail-Making Test A, Digit Symbol Test, D2 Test, Wiener Determination Machine) and memory (Rey Auditory Verbal Learning Test, Benton Visual Retention Test). During follow-up, alternate test versions were used. Neuropsychological deficits were defined as a test score of at least one standard deviation (SD) below the mean of the normal distribution. RESULTS: The pretherapeutic evaluation revealed marked deviations from the normal population; 24% had deficits in intelligence (range 23-31% in different subtests), attention (35%, 23-59%) and memory (48%, 31-61%). The overall percentage of aberrant results was reduced by 12% (memory) to 14% (attention) in the chronic phase up to 12 months after therapy. The improvement in test scores was significant (p < 0.05) in 3 of 4 subtests of attention functions. CONCLUSIONS: The acute tolerance of radiosurgery seems to be very good in these patients, showing no relevant increase in number of patients with neuropsychological deficits. Although the long-term follow-up needs to be further increased, our data indicate a tendency to slight improvement in the overall neuropsychological performance of AVM patients in the chronic phase after radiosurgery.

Adult↗
PubMed1998

Is there a role for heavy ion beam therapy?

The aim of this contribution is to review the radio-oncological rationale of heavy ion beam radiotherapy in the management of cancer. Protons and helium ions are being investigated because of the improved dose distributions, perhaps superior in many clinical situations to those obtainable with photons or electrons. Heavy ions also bear the advantage of superior dose distribution and may additionally provide higher biological effectivity. A substantial database of historical results supports the hypothesis that conformal radiotherapy is superior to conventional radiotherapy. For the selection of patients for ion beam therapy, the following questions have to be evaluated: Can any significant radiation morbidity by conventional treatment expected? Is the radiation morbidity caused by unintended irradiation of non-target tissue outside the planning target volume? Can the tumor control be improved due to dose escalation with less radiation morbidity? A substantial number of patients have been treated by light ion radiotherapy. There are only a few clinical trials attempting to compare conventional photon radiotherapy with light ion radiotherapy. Clinical results with heavy ions such as carbon ions seem very promising in certain tumors. However results of randomized trials are still to be seen. Clearly the control arm has to be designed to be as close as possible to the optimal photon/electron treatment methods in use. The feasibility of heavy ion treatment has been demonstrated worldwide, with more than 10,000 patients. In the near future more centers worldwide will start patient treatments. The wider availability of light ion beams for clinical use will enable the establishment of a database of clinical results and the elucidation of the role of heavy ion beams in the treatment of cancer.

Humans↗
PubMed1998

Use of neutron therapy in the management of locally advanced nonresectable primary or recurrent rectal cancer.

Inoperable locally advanced or inoperable recurrent rectal cancer is a difficult problem. Tenesmus, discharge, bleeding and pelvic pain are frequently present and often are associated with infiltration of the sacral plexus. The value of radiotherapy in managing such patients is being appreciated, although up to 40% of the treated patients have no symptomatic response. Improvement in tumor response and control has been scored through efforts to overcome the radio resistance of the hypoxic tumor cells by neutron irradiation. This article is an account of the activity of neutron radiotherapy in such patients. Over 350 patients were entered in studies comparing neutrons used alone and neutrons used in a mixed-beam treatment schedule. At present no therapeutic gain for long-lasting survival has been achieved; however, local control and pain improvement seems to be better with neutrons than with photons.

Humans↗
PubMed1998

[The radiosurgery of glioblastoma multiforme in cases of recurrence. The Heidelberg experiences compared to the literature].

AIM: To describe the clinical results a prospective phase II study of radiosurgically treated patients with recurrent glioblastoma multiforme. PATIENTS AND METHOD: Since 1986, 62 patients were irradiated stereotactically. Including criteria were residual tumor < or = 5 cm and Karnofsky performance score > or = 70. Twenty-seven patients (mean age 50 years) were treated for recurrent tumor. The planning target volume was defined by the contrast enhancing region demonstrated by magnetic resonance imaging (MRI) scans which were performed in treatment position. A safety margin of 2 to 5 mm was added. The mean dose was 17 Gy. The median interval from the time of initial diagnosis and therapy to radiosurgery for recurrent tumor was 9.6 months. Initial therapy consisted of surgery and irradiation (60 Gy). Survival curves were calculated according to the Kaplan Meier method. Quality of life was evaluated using objective criteria such as neurological findings, frequency of seizures and steroid medication. RESULTS: The median survival calculated from the time of diagnosis was 18 months, calculated from the time of radiosurgery 9 months. 4.5 months after therapy, 50% of the patients showed improved or stable quality of life. CONCLUSION: Radiosurgery demonstrates efficacy in selected patients suffering from recurrent glioblastoma multiforme.

Adult↗
PubMed1998

[Value of radiosurgery in first-line therapy of glioblastoma multiforme. The Heidelberg experience and review of the literature].

AIM: To describe the clinical results and the feasibility of a phase II dose escalation study of small boost target volumes with a radiosurgical technique in patients with positive early postoperative MRI scans. PATIENTS AND METHOD: Since 1986, 35 patients were treated within a concept for first line therapy. Including criteria were residual tumor < or = 5 cm and Karnofsky performance score > or = 70. The mean age was 54.5 years. The treatment concept included an operation for reduction of tumor volume and a postoperative irradiation. The postoperative irradiation was divided in 2 parts: first, a hyperfractionated (1.8 Gy single dose twice a day, 54 Gy total dose) irradiation was performed containing the tumor and the edema with a 2 cm safety margin. Secondly, a radiosurgical boost dose was delivered. The target volume of this radiosurgery was the contrast enhancing residual tumor in early postoperative MRI scans. The median boost dose was 15 Gy. Survival curves were calculated according to the Kaplan-Meier method. Quality of life was evaluated using objective criteria such as neurological findings, frequency of seizures and steroid medication. RESULTS: The median survival calculated from the time of diagnosis was 10.1 months. The 1- and 2-year survival rate were 35% and 6%, respectively. Young age tended to longer survival, patients younger than 53 years had a median survival of 10.4 months whereas patients older than 53 years showed a median survival of 9.2 months. The mean value of the boost volume was 22 cm3. Patients with smaller volumes had a median survival of 10.1 months and patients with bigger volumes showed a median survival of 9.9 months, 4.5 months after therapy, 75% of the patients showed improved or stable quality of life. CONCLUSION: The feasibility of a radiosurgically delivered boost dose after postoperative irradiation could be demonstrated. The observed survival rate is comparable to the survival rates reported in the literature. Whether or not the radiosurgery after postoperative irradiation is able to prolong survival can only be evaluated in a randomized phase III trial.

Adult↗
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↗
PubMed1998

Influence of shock wave pressure amplitude and pulse repetition frequency on the lifespan, size and number of transient cavities in the field of an electromagnetic lithotripter.

Monitoring the generation of cavitation is of great interest for diagnostic and therapeutic use of ultrasound in medicine, since cavitation is considered to play a major role in nonthermal ultrasound interactions with tissue. Important parameters are the number of cavitation events and the energy released during the bubble collapse. This energy is correlated to the maximum bubble radius which is related to the cavitation lifespan. The aim of this study was therefore to investigate the influence of the acoustic pressure amplitude and the pulse repetition frequency (PRF) in the field of a lithotripter (Lithostar, Siemens) on the number, size and lifespan of transient cavitation bubbles in water. We used scattered laser light recorded by a photodiode and stroboscopic photographs to monitor the cavitation activity. We found that PRF (range 0.5-5 Hz) had no influence on the cavitation bubble lifespan and size, whereas lifespan and size increased with the acoustic pressure amplitude. In contrast, the number of cavitation events strongly increased with PRF, whereas the pressure amplitude had no significant influence on the number of cavitation events. Thus, by varying the pressure amplitude and PRF, it might be possible to deliver a defined relative number of cavitations at a defined relative energy level in a defined volume. This seems to be relevant to further studies that address the biological effects of transient cavitation occurring in the fields of lithotripters.

Electric Conductivity↗
PubMed1998

Radiosurgery alone or in combination with whole-brain radiotherapy for brain metastases.

PURPOSE: Evaluation of the treatment outcome after radiosurgery (RS) alone or in combination with whole-brain radiotherapy (WBRT) with special attention to prescribed dose and its influence on local control and survival. PATIENTS AND METHODS: Between September 1984 and January 1997, 236 patients with 311 brain metastases treated with radiosurgery met the following inclusion criteria: one to three brain metastases per patient; no previous WBRT; and Kamofsky performance status (KPS) > or = 50%. One hundred fifty-eight patients treated only with RS received a median dose of 20 Gy prescribed to the 80% isodose line; 78 patients received RS with a median dose of 15 Gy/80% and an additional course of WBRT. RESULTS: For the entire series, overall median survival was 5.5 months, with control of CNS disease achieved in 92% of the treated brain metastases; the results were not significantly different between patients treated by RS with or without WBRT. However, in patients without evidence of extracranial disease, median survival was increased for patients who received WBRT (15.4 vs 8.3 months; P=.08). Additionally, there was a suggestion that increased doses for patients treated with RS only resulted in improved outcome. Four lesions were suspicious for radiation necrosis by magnetic resonance imaging (MRI); in one of the four lesions, radiation necrosis was confirmed histologically. The incidence of transient low-grade toxicity was 18%; symptoms could be treated by the temporary administration of steroids. CONCLUSION: RS is an effective, noninvasive means of controlling brain metastases when used alone or in combination with WBRT. There is a trend for superior local control and especially in patients without extracranial disease for superior survival when RS is used in conjunction with WBRT. Randomized trials would seem to be warranted, comparing the benefit of RS with or without additional WBRT.

Brain Neoplasms↗
PubMed1997

Brainstem tolerance to conformal radiotherapy of skull base tumors.

PURPOSE: The aim of this study was to analyze the long-term incidence of brainstem toxicity in patients treated for skull base tumors with high dose conformal radiotherapy. METHODS AND MATERIALS: Between 1974 and 1995, 367 patients with chordomas (n = 195) and chondrosarcomas (n = 172) of the base of skull have been treated with combined megavoltage photon and 160 MeV proton radiotherapy. Following 3D treatment planning with delineation of target volumes and critical nontarget structures dose distributions and dose-volume histograms were calculated. Radiotherapy was given an 1.8 Gy or CGE (=Cobalt Gray Equivalent) dose per fraction, with prescribed target doses ranging from 63 CGE to 79.2 CGE (mean = 67.8 CGE). Doses to the brainstem surface were limited to < or = 64 CGE and to the brainstem center to < or = 53 CGE. RESULTS: Follow-up time ranged from 6 months to 21.4 years (mean = 42.5 months). Brainstem toxicity was observed in 17 of 367 patients attributable to treatment, resulting in death of three patients. Actuarial rates of 5 and 10-year high-grade toxicity-free survival were 94 and 88%, respectively. Increased risk of brainstem toxicity was significantly associated with maximum dose to brainstem, volume of brainstem receiving > or = 50 CGE, > or = 55 CGE, and > or = 60 CGE, number of surgical procedures, and prevalence of diabetes or high blood pressure. Multivariate analysis identified three independent factors as important prognosticators: number of surgical procedures (p < 0.001), volume of the brainstem receiving 60 CGE (p < 0.001), and prevalence of diabetes (p < 0.01). CONCLUSIONS: Tolerance of brainstem to fractionated radiotherapy appears to be a steep function of tissue volume included in high dose regions rather than the maximum dose of brainstem alone. In addition, presence of predisposing factors as well as extent of surgical manipulation can significantly lower brainstem tolerance in the individual patient.

Adolescent↗
PubMed1997

Dose-response relationship for late functional changes in the rat brain after radiosurgery evaluated by magnetic resonance imaging.

PURPOSE: Only few quantitative data are available on late effects in the healthy brain after radiosurgery. An animal model can contribute to systematically investigate such late effects. Therefore, a model applying radiosurgery at the rat brain was established. A long-term (19 months) follow up study with 66 animals after radiosurgery was carried out. METHODS AND MATERIALS: In 60 animals, an area in the frontal lobe of the brain was irradiated stereotactically with a 15 MV linac. Different doses of 20, 30, 40, 50, and 100 Gy with two field sizes (3.9 and 5.9 mm collimator) were selected, using the integrated logistic formula with input parameters from human brain. The induced alteration of the blood-brain barrier permeability was investigated by means of contrast enhanced magnetic resonance imaging. RESULTS: A first intracranial signal enhancement was observed in one animal 160 days after irradiation with 100 Gy. Beginning at 5 months all animals in the two 100 Gy groups homogeneously showed contrast enhancement, but none of the other groups. This remained until 13 months after irradiation. The volume of contrast enhancement as well as the increase of signal intensity were different between the two 100 Gy groups. After 19 months, the animals irradiated with lower doses also showed contrast enhancements, although not uniformly throughout one group. A maximum likelihood fit of the logistic formula P(D) = 1/[1 + (D50/D)k] to the incidence of late effects for the 5.9 mm collimator at 19 months after irradiation results in the parameters D50 = 37.4(-5.2,+6.1) Gy and k = 4.7 +/- 2.4. CONCLUSIONS: An animal model was established to study late normal brain tissue response. The observed late effects appeared very similar to the estimation of the integrated logistic formula for human brain. Based on these radiosurgery techniques, future experiments will focus on modifications in the irradiation modalities, i.e., irregular volumes, radiation quality or fractionation.

Animals↗
PubMed1997

[Contrast-enhanced MR "magnetization transfer technique". Improved tumor contrast, delineation and visibility of intracranial malignant gliomas and metastases in radiosurgical treatment planning].

AIMS: To improve tumor conspicuity and delineation on contrast-enhanced T1-weighted MR images with and without magnetization transfer (MT) contrast as a strategy to improve the macroscopic boost volume definition in the planning process of radiosurgery in patients with high grade gliomas or metastatic brain lesions. PATIENTS AND METHODS: Thirty-two patients (mean age 47 years) with histologically proven or suspected high grade glioma (n = 12) or metastatic brain lesions (n = 20) were prospectively examined by MR imaging. After the administration of gadolinium dimeglumine (0.1 mmol/kg body weight) the lesions were imaged with a T1-weighted MT-fast low angle shot (FLASH) pulse sequence and with a conventional T1-weighted SE sequence without MT saturation. RESULTS: The mean CNR of enhancing lesions on T1-weighted MT-FLASH was 15 +/- 5 compared to 11 +/- 4 on SE images, representing a significant (p < .01) improvement. The mean tumor diameter of malignant gliomas was significantly (p < .01) larger measured on T1-weighted MT-FLASH images compared to those obtained from T1-weighted SE images and were comparable for metastatic lesions. Lesion conspicuity and delineation were improved in 50% of patients with high grade gliomas and in 35% of patients with brain metastases. Lesion conspicuity was markedly improved in the posterior fossa. Additional contrast enhancing lesions were detected in 10% of patients with metastases on MT-FLASH images. CONCLUSIONS: It is concluded that contrast-enhanced MT-FLASH images may improve lesion detection and delineation in the planning process of radiosurgery in patients with intracranial high grade gliomas or metastases or even alter the treatment approach.

Adult↗