Biomedical subjects
Publications and source records attributed to F Nüsslin.
The photon beam quality factor Q of 6- and 15-MV photon beams has been measured using different types of thimble ionization chambers with various wall, electrode and insulator materials. Some types of chambers seem to overestimate the corresponding Q-value by 0.4% (6 MV) and 0.7% (15 MV), respectively. The effect on the stopping power ratio water to air and on the pertubation correction will be discussed.
The combination of analytical techniques such as PNA and SIMS with a compartmental approach enables the study of the metabolism and biokinetics in humans of several elements by using stable isotopes as tracers. The techniques developed for Te require the administration of greater masses than those used for similar studies performed with radioactive tracers, therefore a test was carried out in rabbits in order to assess the possible influence of the administered amounts on the determination of the biokinetic parameters. The behaviour of the tracers was found to be similar for Te administration of up to 70 micrograms/kg of body weight. An inter-individual variability in the size of the transfer compartment was observed and has to be taken into account.
PURPOSE: Circular collimated X-ray beams rotated in various non-coplanar planes as commonly used in stereotactic linac-based radiotherapy are generating spherical dose distributions with typically steep dose gradients. In case of irregular, especially elongated lesions, this technique fails to conform the shape of the corresponding planning target volume, and a collimator aperture has to be selected which allows for an acceptable dose distribution only on the expense of an excess dose to a larger amount of normal tissue. Therefore we have investigated a bicentric irradiation technique with sequentially treating an elongated target volume over two separated isocenters. METHODS: For the computer simulation studies we used the planning system of the stereotactic unit SRS-200 by Philips. Selected combinations of different collimator aperture were examined systematically by varying the distance between the two isocenters. Dose distributions for a specially developed head-phantom were calculated and analysed. RESULTS: Optimization tables were generated taking into account the geometric quality criteria as well as the corresponding dose maxima. For a given size of the target volume, the appropriate parameters for the bicentric radiation treatment can be chosen. The calculated dose distributions turned out to be independent of the positioning of the two isocenters within the phantom. CONCLUSION: The optimization tables serve to select a set of starting values for the interactive planning process of an elongated target volume resulting in a significant decrease of the overall time for treatment planning of irregular shaped lesions.
BACKGROUND: Complication-free cooperation between physicians and physicists is widely to be found in all areas of biomedical research for a long time. Where both are involved in patient care, however, there are interfaces potentially causing frictions in their relationship. Radiotherapy is considered to be a typical example. KEY ISSUES FOR GOOD RELATIONSHIP: In order to establish a partnership free of tensions 5 attitudes are felt to be essential: interdisciplinary cooperation, recognized professional competency, mutual loyalty among colleagues, actively supported communication, and readiness for conciliation. CONCLUSION: Considering the interdisciplinary attitude of biomedical science as well as appreciating the ethical obligation to the patient good partnership between physician and physicist is necessary and achievable.
A device for computed tomography (CT)-guided percutaneous punctures that is not affixed to the patient and can be used even when the gantry is tilted was developed and tested. In initial patient examinations, the device was accurate within 1.0 mm of the predetermined target point. Experience so far has involved retrobulbar anesthesia and puncture of intervertebral disk space.
Using a commercial system designed for external beam radiation treatment planning a simple method is described for calculating dose distribution in total body irradiation. Scaling factors are applied to keep the range of all distances within the limits preset for the routine use of the planning system. As an example the validity of the method is tested in the lung region which due to dose inhomogeneities is especially critical to an accurate dose determination. Comparing dose calculation and phantom measurements reasonable agreement is obtained.
Since 1976, more than 180 patients suffering from leukemia or aplastic anemia have been treated with BMT and TBI. The improvement of TBI-technique starting from single fraction irradiation without any shielding to different types of fractionation schemes with lung, head and neck shielding and an electron boost to the thoracal wall is shown. A more detailed description of the actual TBI-technique is given; this has been applied to 64 patients to-date. Some clinical results are summarised into four subgroups. Life table analyses are shown for single fraction irradiation as well as for fractionated irradiation separated for high and for low risk patient groups.
Ten ionization chambers (PTW), partly of different type, which all have been calibrated in terms of absorbed dose to water, were used to compare the absorbed dose indicated in a reference geometry at 8 MV X-rays. The standard deviation of the mean value of the absorbed dose determined for all chambers was 0.5%. Since 4 chambers have been calibrated in terms of absorbed dose to water and in exposure, the absorbed dose to water was determined from indicated value according to both calibration procedures. The dose values obtained via the energy dose calibration turned out to be about 2.5% less compared to the result when applying the exposure calibration factor.
A computer program running on a simple desk calculator has been developed for monitoring and recording gynecological high-dose afterloading therapy. For treatment monitoring the multiple-probe AM6-system (PTW-Freiburg) is used which allows for dose measurements in the urinary bladder and the rectum. The probe signals are processed on line in order to indicate the actual dose at the measuring points. After completing the irradiation the treatment is documented. Performing fractionated treatment the measuring data are stored in the computer memory for calculating total accumulated dose. The above-described monitoring and recording [correction of protocolling] system has proven its usefulness during two years of clinical work.
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During the establishment of a new radiooncologic department in a general hospital, a clinical tumor register has been developed for internal patient documentation. The authors describe the general requirements which had to be fulfilled by this tumor register as well as the reasons leading to the purchase of a commercial program package adapted to an irradiation planning system. The structure of the programs and the specification of characteristics are defined. Finally some aspects of organisation regarding the use of the register are mentioned.
A more extensive interpretation of quality control in radio-oncology is opposed to the conception mostly restricted to technical inspections. A review is given of the most important medical and physical aspects of an optimized radiotherapy. Some examples are chosen from the great number of national and international recommendations agreed upon in order to standardize the measures of quality control. Finally some simple radiobiologic models are presented and the corresponding precision requirements are compared with the uncertainties of the dose determination resulting in clinical practice.
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Narrow electron beams with approximately Gaussian radial fluence distributions were extracted from a clinical 42 MeV betatron by means of a special multi-diaphragm lead collimator with either 3 or 7.5 mm diameter of the effective diaphragm. From each narrow beam the dose distribution in water, was measured with an automated scanning system, and the corresponding dose distribution of the point monodirectional source was obtained by deconvolution. As a reference, the fluence distribution in air at the same distance z was used, corrected for multiple scattering in air where necessary. At 10, 20 and 40 MeV, non-linear pear-shaped curves for the root mean square radial excursion, sigma(z), as functions of the depth, with maxima of 12, 19.7 and 27.8 mm at about 70 per cent of the practical range were obtained. The second characteristic function, I(z), the integral of the dose over the transverse plane at depth z, was obtained from the measured broad beam depth dose curve and the associated transverse dose distributions.
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A phantom is described which has been developed for investigating factors depending on the scanner itself and on the scanned object which potentially influence the kind and the extent of motion artefacts on the CT-image. Additionally, the phantom may be applied to qualify assurance measurements in computer tomography. A cylindrical insert mounted on a motor driven axis is fitted centrally in a cylindrical block machined from lucite. Two interchangeable inserts are available, one containing test objects made of various materials, and another one containing small vessels which can be filled with test solutions. The insert positioned in the phantom can rotate either continuously or with the direction of motion being altered periodically. Speed, frequency and arc can be varied within wide limits. Examples demonstrating the static and the dynamic mode of the phantom are shown. By means of the dynamic phantom it is quite easy to directly determine the scan-time of a Computer tomograph.