Andreas Schöggl

High-Resolution Three-Dimensional Contrast-Enhanced Blood Oxygenation Level-Dependent Magnetic Resonance Venography of Brain Tumors at 3 Tesla: First Clinical Experience and Comparison with 1.5 Tesla

Rationale and ObjectivesTo evaluate the clinical potential of high-resolution 3D contrast-enhanced blood oxygenation level-dependent MR-Venography (CE-MRV) for primary brain tumors and metastases at 3 Tesla (T) in comparison to 1.5 T. MethodsEighteen patients with brain tumors were examined using CE-MRV after application of a standard dose of MRI contrast agent (0.1 mmol/kg gadodiamide). CE-MRV is based on a high-resolution 3D flow-compensated gradient-echo sequence with long echo times that uses the contrast-enhanced blood oxygenation level-dependent effect. This technique was performed using the same volume coverage and acquisition time at both field strengths after performing standard imaging sequences. ResultsThe higher spatial resolution of CE-MRV at 3 T showed more details within and around tumors than at 1.5 T. Visibility was enhanced by stronger susceptibility weighting and higher intrinsic signal-to-noise at 3 T. Compared with standard imaging protocols, additional information characterized as tubular and nontubular hypointense structures were found within or around lesions on CE-MRV images. ConclusionsAcquisition of CE-MRV data at 3 T enables spatial resolution to be increased within the same measurement time and with the same volume coverage compared with 1.5 T, thus providing more detailed information. The method may also show the potential to estimate oxygen supply of tumors, especially at high field strengths.

A clinical study of a fibrinogen-based collagen fleece for dural repair in neurosurgery.

Summary.Summary. Background: There is frequently a need for dural grafts to cover defects resulting from retraction, shrinkage, or excision following neurosurgical procedures. Many substances have been tried as possible dural substitution, and different tissues and materials have been evaluated for use in dural repair. Method: The authors performed a retrospective review of 288 consecutive neurosurgical procedures using a fibrinogen based collagen fleece (TachoComb®), a resorbable mesh of collagen from horse tendons, coated with human fibrinogen, bovine thrombin, bovine aprotinin and riboflavin (for marking the coated side), for dural substitution. The fibrinogen and thrombin imitate the last step of the coagulation cascade. On contact with bleeding wounds or other body fluids the coagulation factors dissolve and a link is formed between the collagen carrier and the wound surface. Thrombin converts fibrinogen into fibrin by splitting off peptides. Aprotinin prevents premature lysis of the fibrin clot by plasmin. Findings: Neither superficial or deep wound infections nor aseptic meningitis were noted. We found good fibrous incorporation of TachoComb® into the surrounding normal dura. Postoperative cerebrospinal-fluid (CSF) leaks developed in only five cases, who had to be re-operated, upon as well as one patient with a rebleeding. In another four cases, there was notable subcutaneous cerebrospinal-fluid accumulation without CSF-leak. They required a lumbar cerebrospinal-fluid drainage. Interpretation: We conclude that TachoComb® is a valuable alternative to the patients fibrous tissues for dural repair in cases in which autogenous tissues are either unavailable or insufficient for proper reconstruction.

Shuttle dose at the Vienna Leksell Gamma Knife

The aim of this study was to determine the shuttle dose for all collimator helmets (4, 8, 14 and 18 mm) of the Gamma Knife, model B, in Vienna, Austria. The additional dose accumulated during the transport of the patient in and out of the treatment position should be considered in the dose planning procedure of multicentre treatment regimens and in fractionated stereotactic Gamma Knife radiotherapy. The GafChromic film study was basically used to determine the shuttle dose of all four collimator helmets. In addition, measurements with an ionization chamber (18 and 14 mm collimator--and, for the 18 mm collimator helmet, TLD dosimetry--were performed in order to confirm the GafChromic film data. The shuttle dose ranged between 99.6 and 183.5 mGy, depending mainly on the size of the collimator and the irradiated isocentres at the half-life activity of Co-60 in a brand new Gamma unit. Our film-generated data were in good correlation with the dose levels obtained with the ionization chamber and the TLD dosimetry, showing a dose difference of less than 0.8%. Since it was possible to verify the shuttle dose even for the 4 and 8 mm collimator helmets, we consider it a non-negligible factor and would advocate the inclusion of the shuttle dose in radiosurgical dose planning.

Dosimetry studies with TLDs for stereotactic radiation techniques for intraocular tumours

Between March 1993 and January 1997, stereotactic radiation techniques were used to irradiate 66 intraocular tumour patients with the Gamma Knife (Leksell Gamma Knife, model B unit) at the University of Vienna, Austria. This study investigates the dosimetry for stereotactic irradiation of ocular structures. For the dosimetry program KULA 4.4, Gamma Knife stereotactic irradiation of the eye represents an extreme frontal skull position. In addition, irradiation of the eye may be performed in the usual supine position in exceptional cases only. With the patient in the prone position, the dose planning program has to calculate with a significantly large number of single-beam extrapolations. In our first experiment we measured the isocentre dose for eight different gamma-angle positions, both in prone and supine positions, using TLD measurements in an Alderson head phantom. We found a maximum deviation of +/- 1.6% using these individually calibrated TLDs. In the second experiment we examined the dose cross profiles for the two most frequently used treatment positions (supine position, gamma = 65 degrees, and prone position, gamma = 140 degrees). For this purpose we implanted a specially designed TLD array into the orbit of a human cadaver head. We found excellent agreement of the dose values measured for the isocentre as well as the posterior part of the eye with orbit with deviations of less than -2.7%. However, for the anterior part of the eye, deviations between computer-generated calculations and the TLD measurements were found to range up to -30%. These differences were noticed both for supine and prone positions. For the Gamma Knife stereotactic irradiation of ocular tumours or pathologies, precautions should be taken to avoid significant underdosage in the anterior part of the radiation field.

A novel 675.2 nm diode laser densitometer for use with GafChromic films

In this article we compare the accuracy of a diode laser densitometer emitting 675.2 nm to that of a commercial He-Ne laser densitometer emitting 632.8 nm for GafChromic MD-55 film readout. A Leksell gamma unit (AB Elekta Stockholm, Sweden) Model B with a 14 and 8 mm collimator at the same isocenter (combined 11 mm collimator) was used to irradiate GafChromic MD-55 films. Dose response curves, dose cross profile and FWHM were measured with a custom-designed diode laser scanning device, emitting light at 675.2 nm. The same data were recorded with a commercial He-Ne laser densitometer (PTW FIPS Plus, Freiburg, Germany), emitting light at 632.8 nm. Both measurements were compared to dose cross profiles of a radiosurgery dose planning program (GammaPlan 5.12, Elekta, Sweden). Compared to the commercial He-Ne laser densitometer, the custom-designed diode laser scanning device showed better agreement with the calculated dose cross profile. For two axes, the full width half maxima (FWHM) of the diode laser scanning device was within 0.1 mm deviation compared to the data calculated by the dose planning program. The FWHM of the commercial He-Ne laser densitometer was less accurate (1.6 and 2.1 mm deviation). Our data show that a diode laser scanning device using a light source emitting 675.2 nm increases the accuracy of a GafChromic MD-55 film readout. This greater accuracy may be related to the diode laser measuring the optical density close to maximum absorption of the GafChromic film MD-55 (671-675 nm).

Watertightness and Effectiveness of a Fibrinogen-Based Collagen Fleece (TachoComb®) in Neurosurgery

SummaryBACKGROUND: Meningitis or cerebrospinal fluid rhinorrhoea can occur years or even decades after trauma or operation and can be the first indication of a previously unidentified dural lesion. Preventing cerebrospinal fluid (CSF) leakage with a fibrinogen-based collagen fleece (TachoComb®) was the interest of our clinical study. METHODS: In the present study, we examined the watertightness and effectiveness of TachoComb® following supratentorial/infratentorial as well as skull-base operations. The dura was closed primarily by sutures and covered with a fibrinogen-based collagen fleece to prevent CSF leakage. RESULTS: Twelve patients developed a subcutaneous CSF collection requiring no further treatment, seven patients were managed by lumbar CSF drainages, and three patients had to be reoperated. CONCLUSIONS: Based on these results, we proved the watertightness and effectiveness of this fibrinogen-based collagen fleece.ZusammenfassungGRUNDLAGEN: Eine Meningitis oder eine Liquorfistel kann Jahre bis Jahrzehnte nach einem Trauma oder einer neurochirurgischen Operation erstmalig auftreten. Als Prophylaxe gegen eine Liquorfistel haben wir ein resorbierbares Kollagenvlies, das mit Bestandteilen eines Fibrinklebers beschichtet ist (TachoComb®), klinisch getestet. METHODIK: In unserer vorliegenden Studie haben wir die Wasserdichtheit von TachoComb® in 421 Fällen getestet. Die primär vernähte Dura mater wurde mit einem beschichteten Kollagenvlies bedeckt, ebenso die Schädelbasis nach Schädelbasisoperationen. ERGEBNISSE: 12 Patienten entwickelten ein subcutanes Liquorkissen, welches keiner weiteren Therapie bedurfte. In 7 Fällen wurden die Patienten mit einer Lumbaldrainage behandelt und in 3 Fällen mußte reoperiert werden, um den Defekt zu decken. SCHLUSSFOLGERUNGEN: Basierend auf diesen Ergebnissen können wir die Verwendung von TachoComb® zum Erreichen eines wasserdichten Duraverschlusses empfehlen.

Comparison of Readout Between a New Diode Laser Scanner and a Helium-Neon Laser Densitometer for GafChromic MD-55 Films

GafChromic MD-55 films were irradiated by the Vienna γ-knife unit with a 14 and 8 mm collimator helmet (spherical field of close to 11 mm diameter) at the same isocenter to compare the dose cross-profiles along the x and z directions with different scanning systems. Dose-response curves for GafChromic MD-55 film (Nuclear Associates Model No. 37-041) were measured using two different densitometer systems: a commercial He-Ne laser densitometer (PTW FIPS Plus, Freiburg, Germany) and a newly developed analog diode laser densitometer. For this purpose, we chose the diode laser as the light source, emitting at 675.2 nm with a single-mode surface, measured with a Lock-In Amplifier by a solar cell. The highest uniformity was seen in the change of absorption ranging from 4% to 6%, depending on the polarizing direction of the light with the new scanning system. The reproducibility of the reading method increases from 0.14% in the region of 2 Gy to 0.18% near 16 Gy. Measurements of the dose cross-profiles of the 11 mm collimator with the 675.2 nm laser scanner generally show good agreement with the values of the dose planning program. Reference studies with the He-Ne laser reveal a general tendency between 1.5 and 2.2 mm in diameter as compared to computer-simulated dose profiles and the 675.2 nm laser densitometer values.