Radiobiologia, radiotherapia最新文献

In curative therapy of mouth-cavity and oropharyngeal carcinomas the osteoradionecrosis has to be accepted as a calculated risk with an incidence of 4-35%. It is the question of a radio-caused bone death that comes about by progressive and irreversible morphological alterations at bones and at vessels: Loss of osteocytes, active osteoblasts and osteoclasts (hypocellularity), injury of normal bone metabolism, slackening of regeneration process, extreme susceptibility to infections of the devitalized bone, radio-induced obliterating endarteritis with hyalinization, thrombosis and fibrosing of vessels, obliteration of the lumen and gradual reduction of blood-supply at the level of tissue (hypovascularity and hypoxemia: Aseptic osteoradionecrosis, radio-osteonecrosis). If there is a secondary infection of dental, periodontal or traumatic origin additionally, the condition explodes as septic osteoradionecrosis with the symptoms and findings of radio-osteomyelitis. The osteoradionecrosis begins more frequently in the mandibula than in the maxilla. The cumulative incidence is 30% after 6, 60% after 12, and more than 80% after 24 months. The duration of osteoradionecrosis follows an exponential curve with constant probability of necrosis termination at any moment after necrosis event in which the monthly probability of necrosis healing is nearly 0.06. Risk factors for formation of an osteoradionecrosis are tumor neighbourhood to bones and teeth, tumor and mandibula dosis, tumor stage, irradiation technique, status of teeth as well as moment and carrying out of tooth extractions. Tumors in neighbourhood of mandibula have a fivefold higher risk, with 80 Gy irradiated patients a 2.9-fold and toothed patients a 2.6-fold, altogether high-risk patients have a 17.7-fold higher necrosis risk than low-risk patients. Promoting factors are caries, parodontosis, a periapical pathology, a trauma, irritation by artificial teeth, elective tooth extraction before irradiation, tooth extraction after irradiation as well as jaw operations because of remains or recurrence of the tumor.

On the basis of valid legal arrangement in the GDR to take radiomedical measures in heart pace-maker patients a standardized practice in irradiation planning and a standardized documentation are represented. With this a central registration and analysis of pace-maker patients in radiotherapy can be done to same aspects. The documentation comprehends measures of carrying out radiotherapy, which have been fixed within irradiation planning and risk estimation, and during therapy ascertained measuring values and observations for estimate of heart-circulation-situation of the patient and of the technical state of the pace-maker. The documentation is recommended for application in agreement with the Society for Radiology of the GDR. The Clinic and Policlinic for Radiology of the Martion Luther University Halle-Wittenberg is proposed for central registration and analysis.

For different fields of application in irradiation of gynecological tumors a comparison of isodose distribution is done with "point-shaped" and "line-shaped" 192Ir-source. With the oblateness of dose efficiency distribution towards the axis of source with the "line-shaped" 192Ir-source an improvement of dose distribution occurs in intracavitary irradiation with the lower and more balanced exposure of fundus uteri, especially in irradiation of the endometrial carcinoma. On the other hand the irradiation of vaginal stump renders problematic. In pure vaginal irradiation no differences are found in medically interesting range.

The functional state of the gastric mucosa in dogs after 12.7 Gy abdominal X-ray irradiation was examined. During the first 7 days after irradiation, hypochylia, decrease of proteolytic activity and the H+ (hydrogen-ion) production in the gastric juice was observed. The gastric mucosal cells of rats were examined after the irradiation with 12 Gy to find out the reason for hypochylia. Possibly the reduction of the number of the gastric mucosal cells and their protein content one day after the irradiation, as well as functional disorders of the outer membrane--expressed by the decrease of the intracellular K+ (potassium-ion) level and the ATPase and 5'-nucleotidase activity--may be the reasons for the hypochylia after irradiation.

The dose distribution of a "line-shaped" 192Ir-source was measured in 1,152 measuring points in a water phantom. Using regression analysis the analytical description of dose distribution was obtained. Accomplished comparison measurings with a solid phantom of miramide in 45 measuring points show that the dose distribution can be reproduced well by solid phantom measurings. Taking an ideal line source distribution as a basis, the r-dependence of correction factor, obtained by regression analysis, refers to a dispersion effect. The angle-dependent deviation of dose distribution from the ideal line source can be described by cos-terms with the single and double angle between line source axis and measuring point.

A model to calculate dose distribution behind block shielding is represented in a water equivalent medium for 60Co-radiation. The model is based on integration of spread dose distribution of a pencil beam over the total irradiation area. It is suitable to estimate dose distribution for an irregularly shaped irradiation field.