Dosimetry of soft x-rays in thin liquid layers.

Very thin material layers (<100 microm) partially absorb ionizing radiation of low energy. When irradiating monolayer cell cultures from above, attention must be paid to absorption by the medium. Frequently, the volume of the nutrient medium is variable, and this leads to differences in the radiation doses delivered to the cells. In the present work these conditions were investigated for x-rays of energies between 13 kV and 100 kV in comparison with 60Co gamma rays using chemical dosimetry to measure the absorption by liquid layers between 25 microm and 500 microm thick. When the dose as measured with the ionization chamber was held constant, the dose absorbed in the Fricke solution was shown to increase with decreasing thickness of the layer of liquid because of a dose gradient. The effect of the dose gradient disappeared, however, in thick liquid layers of the Fricke solution by mixing during spectrophotometry. Secondary (photoeffect and Compton) electrons produced in air or filters are responsible for this effect in plastic petri dishes where back scattering at the interface does not occur. This interpretation is suggested by the same results of an analogous experimental setup using gamma rays with a 5-mm-thick Perspex plate. This dose increase in very thin layers, however, could not be verified by irradiating monolayer cells in poured-out plastic petri dishes because the secondary electrons are already absorbed in the remaining liquid film above the cells.

Gonadal protection from radiation by GnRH antagonist or recombinant human FSH: a controlled trial in a male nonhuman primate (Macaca fascicularis).

Chemotherapy and radiation often damage spermatogenesis irreversibly in oncological patients and various approaches to gonadal protection have been tested with equivocal results. In rats, hormonal protection of spermatogenesis can be achieved by blocking gonadotropin secretion. However, whether the same mechanisms can effect gonadal protection in primates remains questionable. To clarify this Issue we conducted a placebo-controlled trial in a preclinical animal model using macaques (Macaca fascicularis). Twenty adult male monkeys (five in each group) were randomized to receive either recombinant human FSH, GnRH antagonist or saline injections (two groups) for 36 days. On day 29 all groups except one saline-treated control group were exposed to a single testicular irradiation of 4 Gy. Every 2 weeks before, during and after the treatment, ejaculates, body weight, testicular Volume and hormones were analyzed until day 539. In addition, repeated testicular biopsies were performed. Testicular Volume and inhibin B decreased significantly in all irradiated groups compared with baseline and with the non-irradiated control group, followed by a gradual recovery of these parameters, which was, especially at the earlier time points, significantly better in the FSH-treated group compared with both other irradiated groups. Irradiation caused a drastic decrease of sperm parameters in all groups, followed by a partial recovery of sperm parameters, which was significantly slower in the early phases of recovery in the GnRH antagonist group compared with the vehicle group. Testicular histology showed a significant depletion on study day 261 in all irradiated animals. In conclusion, in clear contrast to rodent studies, GnRH antagonist treatment did not provide gonadal protection in this primate model. FSH treatment resulted in slightly better recovery of spermatogenesis, which appears to be of no or only little clinical relevance.

Fractionated perioperative high dose rate brachytherapy using a tissue equivalent bendy applicator.

Intraoperative radiation techniques allow an additional local dose in areas at high-risk for local failure. With brachytherapy techniques, perioperative radiation can be fractionated. Fractionated treatment might offer an interesting alternative to a single dose, both to increase the therapeutic ratio and to protect late reacting tissues at risk. The dose distribution for brachytherapy applicators can be optimized using spacer materials. In this prospective study a new tissue equivalent bendy applicator (TEBA) that can remain in situ for several days is introduced, and the feasibility of fractionated perioperative high dose rate (HDR) brachytherapy is examined. 31 patients with different tumours (soft tissue sarcoma, Ewings sarcoma, rectal cancer, and locally infiltrating diseases) were treated. The TEBA was applied, depending on resection status and intraoperative findings. Planning was based on digitized radiographs and CT scans. Perioperative HDR brachytherapy was performed using an individual treatment schedule. In 29 patients perioperative radiation was given and in 26 cases fractionated brachytherapy application was possible. TEBA application time varied from 1 day to 11 days. During this time between 1 and 8 fractions were given with total doses from 10 Gy to 25 Gy. Fractionated perioperative brachytherapy with this technique is feasible and adequate. Further studies will show whether fractionated perioperative treatment using the TEBA technique fulfils its theoretical advantages over single dose intraoperative radiotherapy by decreased late toxicity and increased local tumour control.

CT simulation in nodal positive breast cancer.

BACKGROUND: A variety of solutions are used to match tangential fields and opposed lymph node fields in irradiation of nodal positive breast cancer. The choice is depending on the technical equipment which is available and the clinical situation. The CT simulation of a non-monoisocentric technique was evaluated in terms of accuracy and reproducibility. PATIENTS, MATERIAL AND METHODS: The field match parameters were adjusted virtually at CT simulation and were compared with parameters derived mathematically. The coordinate transfer from the CT simulator to the conventional simulator was analyzed in 25 consecutive patients. RESULTS: The angles adjusted virtually for a geometrically exact coplanar field match corresponded with the angles calculated for each set-up. The mean isocenter displacement was 5.7 mm and the total uncertainty of the coordinate transfer was 6.7 mm (1 SD). Limitations in the patient set-up became obvious because of the steep arm abduction necessary to fit the 70 cm CT gantry aperture. Required modifications of the arm position and coordinate transfer errors led to a significant shift of the marked matchline of > 1.0 cm in eight of 25 patients (32%). CONCLUSION: The virtual CT simulation allows a precise and graphic definition of the field match parameters. However, modifications of the virtual set-up basically due to technical limitations were required in a total of 32% of cases, so that a hybrid technique was adapted at present that combines virtual adjustment of the ideal field alignment parameters with conventional simulation.

The relative biological effectiveness of low doses of 14 MeV neutrons in steady-state murine spermatogenesis as determined by flow cytometry.

The relative biological effectiveness of 14 MeV neutrons in the low-dose range < or =1 Gy has been determined in differentiating and differentiated spermatogonia. Male NMRI mice were exposed to single doses of 2 cGy to 3 Gy of (60)Co gamma rays or neutrons. The ratios of testicular S-phase cells, 4c primary spermatocytes, and elongated spermatids were quantified by DNA flow cytometry 2 to 70 days after irradiation and were found to decrease. Histological samples and testis weight were analyzed in parallel. Doses of 2-5 cGy neutrons and 10-50 cGy gamma rays significantly (P<0.05) decreased the proportions of S-phase cells, spermatocytes and elongated spermatids at 4, 14 and 28 days postirradiation. For S-phase cells, the biphasic shape of the cell survival curves was described with a D(50) of 5 cGy neutrons. The D(50) for (60)Co gamma rays and the relative biological effectiveness could not be determined. The relative biological effectiveness of neutrons at 50% reductions of testis weight, primary spermatocytes, and elongated spermatids were 2.5, 10.0 and 6.1, respectively. This in vivo assay is interesting because of its sensitivity at dose ranges that are relevant for exposures in the environment, the workplace and radiotherapy.

[The modification of programmable pacemakers by therapeutic irradiation]. / Beeinflussung programmierbarer Schrittmacher durch therapeutische Bestrahlungen.

BACKGROUND: More than 300,000 pacemakers are implanted worldwide. During radiation therapy a damage of the pacemaker electronic is possible. METHODS: Twenty pacemakers have been irradiated with photons or electrons experimentally in three different situations: a) pacemaker and pacemaker electrode outside of the irradiation field: b) pacemaker outside, pacemaker electrode inside the irradiation field; c) all things inside the irradiation field. RESULTS: The voltage in the pacemaker electrode produced by the electric field of the accelerator did not exceed 0.8 mV if the electrode was outside the irradiation field. Induced voltage was up to 1.2 mV during irradiation with electrons (18 MeV) and the electrode being inside the treatment field with more than two thirds of its length. After delivering of not more than 10 Gy (photons) to the pacemaker, a decreasing amplitude of the pacemaker pulse occurred. The pulse frequency did not show any deviation. This seems to signal a severe early irreversible damage of the pacemaker that may cause sudden breakdown days or weeks after radiation. Two pacemakers showed a complete breakdown after irradiation with not more than 10 Gy. The others had a complete breakdown beyond doses of 50 Gy. CONCLUSIONS: It is recommended to keep CMOS pacemakers outside the treatment field and to explant if the dose to it was higher than 10 Gy.

[The physical and technical outlook for neutron therapy in Germany]. / Physikalisch-technische Perspektive der Neutronentherapie in Deutschland.

All five fast neutron therapy centres in Germany use low energy cyclotrons or neutron generators and are, therefore, at the low energy end of the 21 neutron therapy facilities presently in use worldwide. The depth dose characteristics are worse than for 60Co gamma rays, the absorbed dose rate is too low and the treatment is technically restricted because of the lack of those modern features like multileaf collimators and full gantry rotation that are available with modern linear accelerators. A survey of the statistical and methodical data on the neutron treatment in Germany is presented. To avoid masking the potential biological benefits of high LET neutron irradiation by the use of suboptimal equipment and to utilise the real therapeutical benefit for specific tumor types, the German neutron therapy centres urgently need modernization of their outdated facilities. Specific recommendations of how to meet the requirements of modern neutron therapy are given.

[Direct radiographic magnification and radiation exposure]. / Direktradiographische Vergrösserung und Strahlenexposition.

The advantage of microfocal X-ray units is the production of high-resolution magnification radiographs. Up to a magnification of x 4 the exposure equals that of a conventional radiograph. Some filter materials have been tested, aluminium filtration was found to be the best choice.

[Direct radiographic magnification in combination with digital radiography for bone imaging]. / Direktradiographische Vergrösserung in Kombination mit digitaler Radiographie für die Skelettdiagnostik.

The usefulness of direct radiological magnification is inversely related to the resolution of film-screen systems when very small focal spots are used. Thus, spatial resolution of digital luminescence radiography (DLR) may closely approximate that of high-detail screens at the expense of a more restricted field of view. Apart from the major drawback of limited spatial resolution, DLR makes it possible to take full advantage of image-processing techniques and an unmatched dynamic range.

[Quality assurance in x-ray installations for therapy in accordance with the x-ray regulations]. / Qualitätssicherung bei Röntgeneinrichtungen zur Therapie gemäss Röntgenverordnung.

For the conventional X-ray therapy the Röntgenverordnung demands the examination of the dose rate in the radiation beam. The measurements and the results are demonstrated. Over a long period the X-ray equipment shows a constant dose rate. Controls of the technical devices and situations of danger are explained.

[How safe are older x-ray generators]. / Wie sicher sind ältere Röntgengeneratoren?

An incident with a high-voltage generator more than 25 years old was the occasion for a discussion of the safety of such generators. A control timer broke down during the exposure period, and before the radiographer was able to react the X-ray tube imploded. The young patient suffered increased exposure and partial grade 3 burns. If such a breakdown occurs during exposure the radiographer has to turn off the generator by hand. This is the only way of preventing injury to the patient. Owners of such units must be aware of their particular responsibility and should train their personnel accordingly. In case of a breakdown only well-trained staff can act immediately, in the knowledge that only a few seconds are available before the patient suffers physical injuries. The fault mentioned should have been expected and it could happen again any time with such an old installation.

[Quality assurance in the microfilming of x-ray pictures]. / Zur Qualitätssicherung bei der Mikroverfilmung von Röntgenaufnahmen.

Microfilming of X-ray films has become more topical owing to the amendment of the X-ray regulations. The storage of X-rays as reproductions on an image or data carrier is expressly envisaged as a possibility in the text of the regulation. The quality of transfer must be insured and the copies must be legible. In microfilming, the latitude and the resolution capacity of the microfilm and remagnification are appropriate as parameters of image quality. Testing of seven filming systems shows a major range of variation of both parameters; in some cases, the results led to reexamination of the camera adjustment and developer chemistry. A test of constancy of filming analogous to direct radiography appears necessary. A corresponding norm does not exist at present.

[High-contrast radiographs for field control and field documentation in radiotherapy with high-energy photons]. / Kontrastreiche Aufnahmen zur Feldkontrolle und Felddokumentation in der Strahlentherapie mit energiereichen Photonen.

In ambitious radiotherapy with individually shaped irradiation fields, high-contrast field radiography is necessary for fine adjustment, control and field documentation. If intensification foils made of materials with medium or high atomic numbers such as copper, iron and lead are used, the film lying between the foils is mainly darkened by the secondary electrons released from the material of the front foil. Within the range of 1 MeV to 15 MeV, high-contrast radiographs are produced by means of copper or steel foils which are clearly superior to lead foils. Steel foils are to be preferred to copper foils because of their rigidity and the firmness of the polished surface. Usual X-ray diagnosis films with steep graduation can be used as film material for field control radiography performed in double exposure technique. A new insensitive film not applied hitherto in X-ray diagnosis allows to prepare field documentation images of high quality which are exposed during the whole irradiation time. This is also important for perpetuation of evidence.

[Radiation dose to children from cranial examinations with new-generation computed tomographic equipment]. / Zur Strahlenbelastung von Kindern bei Schädeluntersuchungen an Computertomographen der neuen Generation.

Using phantoms of children simulating a child of 6 month of age and another one aged 6 years, the authors measured the amount of radioexposure of the lens of the eye, the thyroid and of the gonads. The two computer tomographs Somatom SF and Tomoscan 300 under examination, produced radiodoses of comparable magnitudes. Both devices allow additional examination techniques of particularly high economy. It was found that in cranial CT the exposure of the lens to radiation is generally below 1 R if the orbitae are not situated in the plane of section. If a distance of 2-3 cm is maintained from the orbitae, the dose remains below 0.5 R. Protecting the gonads is meaningful in a 6-year-old boy, whereas covering-up of the thyroid reduced the dose only slightly.

[First clinical experiences with a new large frame intensifier in thoracic diagnosis]. / Erste klinische Erfahrungen mit einem neuen Grossbildverstärker in der Thoraxdiagnostik.

In 350 patients with 870 pathologic findings comparative blind analysis of conventional chest films and biplane 100 mm photofluorographic images taken with the large-field image intensifier revealed high accuracy in the evaluation of coin lesions, hilar and pleural pathology, pulmonary vasculature and the right paratracheal stripe. Moderate central interstitial edema, more subtle interstitial changes particularly in the lung periphery including Kerley's B-lines, and calcifications in the hilum or the aortic arch are not visible in all cases for the evaluation of lesions of the ribs special films continue to be mandatory. Lateral views are of good quality. The spatial resolution of the large-field image intensifier was measured to be 4.5-5.2 LP/mm at the output phosphor, the spatial resolution of the 100 mm intensified images ranges from 2.6-3.8 LP/mm in the center. Mean skin dose was found to be 6.3 mrd in the p.a. projection which is less than 5% of the values registered in non-intensified photofluorography and even by factor 5 lower than in conventional chest x-ray using rare earth screens.