RESUMEN

The current induced in the outer circuit of a fast response ionization chamber exposed to pulsed radiation consists of two components, a fast one induced by free electrons and a slow one induced by ions. The fast electron component may be used for the representation of the shape of the ionizing pulse. In order to avoid interference with the slow ion current, the latter has to be removed from the signal. This is achieved by deriving a voltage course from the chamber signal which fits the shape of the ion component and subtracting this from the entire signal. The function of the electronic circuit used for this purpose is described. Some considerations about the time resolution of the chamber gas are to be found in the appendix.

Asunto(s)

Asunto(s)

RESUMEN

An experimental model in the rabbit is presented which is suitable for analysis of clinically relevant, early side-effects of combined upper abdominal IORT and ERT. Fractionated ERT alone given through an upper abdominal a.-p. field including the entire stomach caused gastric ulcerations within < or = 58 days. Latent times decreased with increasing dose and the ED50 for occurrence of ulcers was 39 +/- 3.3 Gy. Single doses of IORT of 20-40 Gy alone administered through a 2-cm diameter field localized on the coeliac axis and carefully excluding any intestinal mucosa caused neither gastric ulcerations nor other clinical symptoms. When ERT with 40 Gy was preceded by IORT with 20-40 Gy or by sham IORT, 13 out of 15 animals developed ulcers after latent times which in a life-table analysis were shown to be significantly shorter than after ERT alone. However, a statistically significant IORT dose-dependence of latent time or incidence of ulcers could not be demonstrated in the present experiment. The most significant histological changes were observed in the areas of gastric ulcers. Already during ERT, the mucosal epithelium was depleted and regenerative activity was evident in spite of ongoing fractionated irradiation. However, profound irregularities in glandular structure and distribution, as well as number of proliferating epithelial cells were still present in healed ulcers at 80 days. In summary, IORT to the coeliac artery did precipitate the development of gastric ulcers induced by subsequent ERT. On the one hand, the data indicate that the surgical procedure of IORT did contribute to this effect. On the other hand, IORT to the coeliac artery could cause transient, functional alterations in blood supply to the depending organs, i.e. the stomach, and could thus precipitate the development of radiation-induced ulcers.

Asunto(s)

RESUMEN

Disc degeneration, if it appears relatively early, progresses rapidly with inadequate bone compensation for stabilisation of the area, or in the presence of anatomic variation of the vertebrae with short sagittal diameters, there may be tissue proliferation and edema in the bone marrow and vascular granulations within the disc. We demonstrated these changes in 17 patients by means of MRT which shows edema of the bone marrow and contrast enhancement within the disc. All these patients had severe symptoms. There were no significant neurological findings since in general there was no disc prolapse. The MRT characteristics of this condition are described and correlated with the clinical and radiological features. The use of Gd-DTPA and subtractive spin-echo and gradient-echo sequences in the differential diagnosis from infective discitis is discussed.

Asunto(s)

RESUMEN

42 patients with known malignancy and vertebral compressions underwent MRI. Sagittal T1-weighted spin-echo images pre and post Gd-DTPA, out of phase long TR gradient-echo images (GE) and short T1 inversion recovery images (STIR) were obtained at 1.0 T. The results were confirmed by histology (6/42) or clinical data (28/42) and follow up MRI studies (8/42). In 39 of 42 cases a correct differentiation between osteoporotic and tumorous vertebral compression fractures was possible by quantification and correlation of SE and GE signal intensities. Gd-DTPA did not improve differential diagnosis, since both tumour infiltration and bone marrow oedema in acute compression fracture showed comparable enhancement. STIR-sequences were most sensitive for pathology but unspecific due to a comparable amount of water in tumour tissue and bone marrow oedema. Susceptibility-induced signal reduction in GE images and morphologic criteria proved to be most reliable for differentiation of benign and tumour-related fractures. In the rare cases of single and nearly complete vertebral compressions with complete loss of bone marrow, differentiation with MRI was not possible.

Asunto(s)

RESUMEN

A specialized applicator system for intraoperative radiation therapy using high energy electrons of a linear accelerator has been developed and manufactured, regarding the specific situation that there is no dedicated linear accelerator available at the surgery facility. Additionally, long lasting interruptions of the daily routine irradiations are hardly tolerable. A significant improvement of the procedure could be achieved developing applicators, which are divided into two halves. Positioning the lower part of the applicator into the patient at the operating room already, the transportation and the irradiation of the closed patient is possible. Adapted to the linear accelerator in use, a Siemens Mevatron KD having electron energies in the range from 6 to 21 MeV, the dosimetric properties of the system have been optimized by iteration. Excess dose values near the applicator walls could be avoided completely. A rapid decrease of the leakage dose could be realized.

Asunto(s)

Asunto(s)

RESUMEN

Deep and superficial body temperatures were measured by in vitro and in vivo experiments, using a fluoroptic procedure and a variety of magnetic and electromagnetic fields, in the course of magnetic resonance imaging (0.35 T; 1.5 T). In vitro experiments were performed to select and check the appropriate temperature method. Temperature measurements in the human body were carried out centrally (esophageal and rectal measurements). In vivo experiments in 30 volunteers showed no significant changes (p = 0.05) in central or peripheral temperatures resulting from the application of static or dynamic fields or radiofrequency.

Asunto(s)

RESUMEN

Between 1975 and 1981 69 patients suffering from Hodgkin's disease stage I to III were treated by radiotherapy exclusively. In contrast to the standard modalities the mantle was treated only through a ventral portal with dorsolateral boost to the posterior mediastinum. The geometrical treatment arrangement and the modalities of dose application yielded favourable dose distributions and single doses within the target volume. The analysis of failures showed no in field-failure, six marginal recurrences, and 17 distant failures, which are not related to the technique of irradiation. The described technique of mantle irradiation seems to be equivalent to the standard technique with regard to tumor control and side effects.

Asunto(s)

RESUMEN

15 patients with locally unresectable pancreatic carcinomas were treated by IORT and bypass surgery. 13 patients without distant metastases were additionally treated by external beam irradiation. Although only one patient had a local failure, the median survival was only eight months. Severe complications were seen in eight patients, gastrointestinal bleeding occurred in six patients and was the cause of death in three patients. The stop of weight loss and the impressive pain relief within ten days after IORT demonstrate the significance of this treatment modality with respect to palliative effects.

Asunto(s)

RESUMEN

By means of registration of somatosensory (SSEP) and visual (VEP) evoked potentials under the influence of different magnetic and electromagnetic fields of Magnetic Resonance we investigated the influence of Magnetic Resonance Imaging (MRI) on human nervous system (all measurements with an 1.0 T MR imager are performed outside and inside the static magnetic field, before and after MR imaging). In vivo experiments on 20 healthy volunteers show in SSEP registrations as well as in VEP-registrations no measurable influence on nerve conduction. The measured latencies before and after MR imaging are found inside the standard values which are valid for healthy volunteers. In vivo experiments at field-strengthens up to 1.0 Tesla show no significant changes of the central and peripheral conduction velocity with human beings.

Asunto(s)

RESUMEN

Since 1983 the computerized record and verify system Mevamatic 3 was tested in connection with the linear accelerator Mevatron 77 (Siemens Company). In consequence of the software development the handling of the system was improved for the clinical routine with the result of a fully utilizable system. The topics of this report are the description of the hardware, the functions of the system, the software development and some possibilities for improvements in the future.

Asunto(s)

RESUMEN

Evaluating the increase of signal intensity on the T1-weighted pulse sequences is the simplest way of measuring the enhancement in MR studies of the breast. A good homogeneity within the coil is a prerequisite for such an evaluation. A coil with 3 parallel windings and good homogeneity is presented.

Asunto(s)

RESUMEN

Deep and superficial body temperature was measured by in vitro and in vivo experiments, using a fluoro-optic procedure and a variety of magnetic and electromagnetic fields in the course of magnetic resonance tomography. The in vitro experiments had shown that measured temperature changes resulting from a static magnetic field were reversible and could be reproduced readily. Temperature measurements in the human body were carried out centrally (oesophageal and rectal measurements) and at the periphery (intravascular). In vivo experiments on 30 experimental subjects showed no significant changes (p = 0.05) in central or surface temperatures as a result of static or dynamic magnetic fields or electromagnetic high frequency fields.

Asunto(s)

RESUMEN

Apparatus for immobilizing the patient's head in an identically reproducible position is required, if the advantages of exact quasi-3-D-therapy planning are to be fully exploited for the irradiation of irregular target volumes in the head and neck area. The topics of this report are the production and application of individual thermoplastic masks in connection with special head supports for CT planning scans, simulation and irradiation.

Asunto(s)