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AIMS AND PURPOSE: Radiotherapy is an essential and reliable element of the treatment armamentarium in oncology. Numerous rules, regulations, and protocols minimize the associated risks. It can, however, never be excluded that errors in the treatment delivery chain result in inadequate tumor doses or unnecessary damage to organs at risk. A legal framework governs the management of such incidents. The most important European and North American regulations are reported. RESULTS: Various directives issued by the European Union are differently implemented nationally. This applies particularly to the characterization of incidents that must be reported to authorities. Reporting thresholds, audit systems, and the extent of the integration of voluntary reporting systems vary. CONCLUSION: Radiotherapy incidents are dealt with differently on an international level. Changes are to be expected based on the European Basic Safety Standards Directive that is currently being prepared and will have to be implemented nationally in due course.

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Using a non-invasive mask this patient fixation system for stereotactic radiotherapy allows one to perform fractionated irradiation. Measuring the statistical quantities of patient motion and positioning uncertainties and calculating its effect on a spherically symmetric dose distribution showed that there is no severe disadvantage in most cases. Only if small field-size, excentric target volume localisation and extreme proximity to an organ at risk coincides have the statistical effects to be taken into account. The greatest measured standard deviation for positioning uncertainty was 2.3 mm. Its effect on the dose distribution with a field size of 9.1 mm increases the diameter of the 80% isodose to about 115%.

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Three-dimensional (3-D) radiotherapy planning is applied for the conformation therapy of a bronchial carcinoma. The treatment technique, using dynamically controlled shielding blocks, and the treatment planning procedure are described. The method has now been in clinical routine since 4 years; problems with the patient's positioning are discussed.

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An irradiation phantom was used to measure dose increases using the backscatter of different materials (titanium, steel, lead, aluminium). Telecobalt-60 and 8-MV photons were used for the irradiation. The irradiation dose was measured by means of a defined X-ray film blackening. The most important parameter was to find out whether under simulated conditions, undesirable hot spots occur. We were able to demonstrate that a 12.5 to 16% increase in the radiation dose can be observed for titanium and steel at a distance of 0.45 mm from the metal specimen. A comparison between titanium and steel did not demonstrate a relevant advantage for titanium. Therefore, adjuvant percutaneous radiation therapy should not have any influence on the life of the implant, if the soft tissue layer is of sufficient thickness. The available literature is reviewed and presented in tables.

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Very small electron beams show considerable reduction of the dose output factor, the therapeutically relevant range, the practical range and the therapeutically relevant field size, compared to broad beams. The first three effects were measured on the central beam axis for different quadratic field sizes and are presented in the first part of this publication. A simple field zone method for calculation of irregular shaped electron beams was developed from the different depth dose curves. The method allows the determination of the maximum dose and the 80% range with sufficient accuracy for practical purposes. The examination of the reduction of the therapeutically relevant field size and the consequences following thereof with respect to the adequate electron therapy of a small irregular target volume will be published in a second part.

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The researches of Pauwels and those following him have demonstrated that the subchondral bone density distribution below the surface of a joint is a metrical parameter which mirrors the predominant stress acting on that joint. Their technique of x-ray densitometry cannot, however, be used during life. By employing computer tomography, a new method has been developed--CT-osteoabsorptiometry (CT-OAM)--which can be used to obtain the density distribution pattern in the living subject. By means of a comparative investigation on specimens which were examined both with traditional x-ray densitometry and with CT absorptiometry, it has been shown that the new method can produce the same results, but providing the great advantage to be used on the living. In addition, the density distribution pattern of the glenoid cavity has been examined in patients with various shoulder conditions, and also in gymnasts who exercise on the rings. The distribution of subchondral bone density showed different patterns in the different groups examined. Both the comparison of the methods and the subsequent study confirmed that CT osteoabsorptiometry enables assessment to be made of the individual long-term stresses acting on a living joint.

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A method of making a visual display of subchondral mineralization in the major synovial joints is described. Unlike existing procedures, it can be used on the living subject. A modified application of computed tomography-densitometry, computed tomography-osteoabsorptiometry makes it possible to explore the mechanical adaptability to the prevailing mechanical force. This claim is based upon the comparison of information obtained from 20 anatomical specimens with CT-osteoabsorptiometry and x-ray densitometry of sections; both methods yielding virtually identical results. The distribution of the subchondral density was then expressed as a map of the articular surface with the aid of an image analyser. This method can make a useful contribution to basic clinical research, as well as providing a diagnostic technique which can also be used for observing progress after a corrective osteotomy or any other procedure causing a change in mechanical function. Examples of its use on living patients are given.

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To estimate subchondral mineralisation patterns which represent the long-term loading history of individual joints, a method has been developed employing computed tomography (CT) which permits repeated examination of living joints. The method was tested on 5 knee, 3 sacroiliac, 3 ankle and 5 shoulder joints and then investigated with X-ray densitometry. A CT absorptiometric presentation and maps of the area distribution of the subchondral bone density areas were derived using an image analyser. Comparison of the results from both X-ray densitometry and CT-absorptiometry revealed almost identical pictures of distribution of the subchondral bone density. The method may be used to examine subchondral mineralisation as a measure of the mechanical adaptability of joints in the living subject.

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Bone density has been assessed during and after radiotherapy of metastases of the spine using quantitative computed tomography (QCT) in 19 patients with osteolytic vertebral lesions. All patients underwent external photon radiation with a total dose of 40 Gy over a period of 4 weeks. Measurements of vertebral mineral density were performed at the beginning, at the end, and 3 months after radiotherapy. In 13 patients with osteolytic metastases, radiotherapy achieved complete release of pain; it was unsuccessful in the remaining 6 patients. Immediately after successful radiotherapy, osteolytic metastases showed a decrease of bone density of 24.7% followed by an increase of 60.6% 3 months later. Normal bone surrounding the osteolysis showed an increase of density at the end and 3 months after radiotherapy. QCT has proved to be a helpful tool in assessing successful radiotherapy of metastases of the spine.

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At the Radiotherapy Department of the University Hospital of Freiburg i.Br., an additional diaphragm controlled by an electronic system in dependence on the angles was developed for the optimization of irradiation planning, i.e. administration of the therapeutically necessary dose to the target volume and, at the same time, sparing of risk organs.

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Thanks to the improved devices at the Royal Marsden gun the loading time for gold seeds has been reduced by about one third as well as the radiation exposure has been reduced to about one tenth, due to the fact that the fingers are not so long close to the seeds. The reliability and the manageability has been improved, too.

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Simulator method and computed tomography use different pictures for measurements of the tumor volume for therapy planning: X-ray pictures taken from two different directions can only show the indirect volume of the tumor, while CT pictures give information of the real size of the tumor. For estimation of the value of the two methods therapy planning was performed by the simulator method in 34 patients with carcinoma of the prostate (T1-T3) and the results were added to CT pictures. Comparison of the two methods resulted in equivalent consequences. Therefore economic aspects should be taken into account for selection of a special method of radiation therapy planning.

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The structure of the rod outer segment disc-membrane in vivo was studied by X-ray low-angle scattering. The experiments were made on frogs under narcosis. Diffraction patterns corresponding to a resolution of 1.5 nm could be obtained from the membrane stacks of the rod outer segment discs. For the analysis of the measured diffraction pattern a new special computer procedure was elaborated. Among other generalizations of the theory, it was taken into account that the electron densities in the inter- and intra-disc spaces differ from the mean electron density of the whole stack. The consideration of this possibility, together with an exact experimental measurement of the isotrope background scattering, led to a mathematically unique solution. The calculated electron density profile apparently is a distinct asymmetric bilayer. The electron density of the side of the membrane which is in contact with the disc lumen is higher than the electron density on the side in contact with the cytoplasm. Therefore, a localization of rhodopsin or of other high molecular proteins mainly on the cytoplasmatic edge of the membrane can be excluded for the rod outer segment discs in vivo.

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