SU-E-T-313: Probe-Type Experimental Dosimetry in Terms of Absorbed Dose to Water in Photon-Brachytherapy a Proposal for a Radiation-Quality Index.

PURPOSE: In photon-brachytherapy (BT), all data for clinical dosimetry (e.g., the dose-rate constant) are not measured in water, but calculated, based on MC-simulation. To enable the measurement of absorbed dose to water, DW, in the vicinity of a source, the complex energy-dependence and other influence quantities must be considered. METHODS: The detectors response, R=M/D, is understood as product of a detector-material dependent 'absorbed dose response', Ren, and Rin, the 'intrinsic response'. Ren is described by the Burlin-theory and because of dissimilarities between the detector-material and water, will have energy dependent correction factors which convert Ren into the clinically relevant DW,Qo=MQo × ND,W,Qo. To characterize BT- source-types, we propose a new 'radiation-quality index' QBT=Dprim(2cm)/Dprim(1cm), the ratio of the primary-dose to water at r=2cm to that at the reference distance r=1cm, similar to external beam dosimetry. Although QBT cannot be measured directly, it can be derived from primary and scatter separated dose-data, published as consensus data e.g., in the Carlton AAPM-TG-43-database. RESULTS: Mean QBT-values are: for nine HDR and four PDR 192Ir-sources: 0.2258±0.5%; one 169Yb- source: 0.2142; and one 125I-source: 0.1544. CONCLUSIONS: The main benefit of this new QBT-concept is that a type of BT-dosimetry-detector needs to be calibrated only for one reference radiation-quality, e.g., for Q0=192Ir. To measure the dose for different source-types, DW can be determined using calculated radiation-quality conversion factors kQ,QoBT, to be included in the AAPM-database and to be provided by the manufacturer for each detector-type. Typical BT-dosimetry-detectors are plastic scintillation detectors, radiochromic film, thermoluminescence detectors, optically stimulated detectors, and small volume ionization chambers. Recently, different DW(1cm)-primary standards have been developed in several European NMIs, enabling to calibrate BT-radiation- sources and BT-dosimetry-detectors and allowing to verify MC-calculated dose-rate constant values. The proposed definition of QBT has to be discussed internationally to find broad consensus.

[Therapy relevant weak sites in industrial quality assurance of 106Ru eye plaques]. / Therapierelevante Schwachstellen bei der industriellen Qualitätssicherung von 106Ru-Augenapplikatoren.

BACKGROUND: Beta emitting 106Ru applicators manufactured by Bebig GmbH (Berlin, Germany) are widely used to treat intraocular tumors. The applicators are fixed to the bulbus and removed after several days. The following therapy relevant defects have been detected by an internal clinical acceptance test: risk of leakage and inconsistent dose-rate specifications by the manufacturer. In the meantime, components of the internal clinical acceptance test have been adopted successfully by the manufacturer of the 106Ru ophthalmic plaques. MATERIAL AND METHOD: 106Ru ophthalmic plaques were tested with the following internal clinical acceptance tests: visual inspection, surface contamination, leakage, and dose-rate verification. The surface contamination test consists of a wet wipe test at moderate pressure. For the leakage test of the 106Ru ophthalmic plaques a clinically relevant scenario was developed in which the contact of the applicator with human tissue is simulated. In the course of it the applicator is inserted into Ringer's solution for several days. The certified energy dose-rate statements of the manufacturer are examined with a 1 mm3 plastic scintillator for consistency. RESULTS: During the internal clinically acceptance tests of 106Ru ophthalmic plaques of different size the following results were obtained: The leakage test was performed with seven applicators and yielded measurements for two 106Ru ophthalmic plaques that were significantly higher than those of a dummy sample. The highest value of a wipe test was 57 Bq (Figure 1). The highest value in Ringer's solution was 520 Bq (Figure 2). During the dosimetry consistency checks of the certified dose-rate specifications for 14 applicators, six applicators were in good agreement with a variation coefficient of 2.6%. For the other eight applicators the deviations were between -37% and +74% (Figure 3), i.e. the range of the unaccepted applicators amounts to 111%. The results were representatively verified through external assessment. CONCLUSION: Grave therapy relevant shortcomings of the industrial quality assurance of ophthalmic plaques were uncovered by experimental cross-checks. It is necessary that every radioactive device is internally examined before its use. The internal clinical acceptance test of the 106Ru ophthalmic plaques can easily be adopted by other hospitals.

Physical properties of endovascular stents: an experimental comparison.

PURPOSE: Different endovascular stent types (AVE Bridge, AVE Bridge X, Memotherm, Palmaz Large, Palmaz Medium, Palmaz-Schatz Long-Medium, Perflex, S.MA.R.T., Symphony, and Wall-stent) of 4 cm length and 8 mm diameter were subjected to standardized physical tests. MATERIALS AND METHODS: The metal mass of each stent was assessed by weighing. The balloon-expandable stents were pneumatically tested for hoop strength. In self-expanding stents, radial resistive force and chronic outward force were determined with use of a loop test. Stent delivery system pushability was assessed in a crossover model. Stent radiopacity was analyzed quantitatively. RESULTS: The hoop strength of the balloon-expandable stents ranged from 15.8 N/cm (Perflex) to 28.9 N/cm (AVE Bridge X). The stent weight increased with greater hoop strength (Perflex, 0.046 g/cm vs. AVE Bridge X, 0.061 g(cm). The self-expanding stents had a radial resistive force between 0.39 N/cm (Wallstent) and 1.7 N/cm (Smart). The flexible balloon-expandable stents showed pushability values between 0.13/N (AVE Bridge) and 0.20/N (Perflex). The self-expanding stents had flexibilities between 0.13/N (Memotherm) and 0.24/N (Symphony). Radiopacity assessed with use of a phantom simulating the iliac region ranged from 92 (Palmaz Large) to 115 (AVE Bridge) on a 256-point gray scale (0 = black, 256 = white). CONCLUSIONS: There is no stent with ideal physical properties. However, depending on the characteristics of the arterial lesion to be treated, the most appropriate stent can be chosen.

[Emergency rescue in accidents with HDR afterloading units]. / Notfallbergung bei Unfall an HDR-Afterloading-Anlagen.

PROBLEM: HDR brachyradiotherapy has minimized the exposure to radiation of the personnel working in this field. Nonetheless there are periodically reported troubles with afterloading units concerning the retraction of sources that require immediate action for the limitation of possible damage. LEGAL PRINCIPLES ACCORDING TO THE GERMAN REGULATION CONCERNING PROTECTION AGAINST RADIATION (STRAHLENSCHUTZVERORDNUNG = STRLSCHV): If in afterloading brachyradiotherapy the radiation source remains extended through malfunction we deal with an emergency according to the StrlSchV. The rescue personnel should be chosen in accordance with section 50 StrlSchV (Table 1). ORGANIZATION OF THE RESCUE OF THE PATIENT: The quickest possible rescue of a patient in an emergency demands an unequivocal definition of responsibilities. Our recommendations in this instance: the physicist is responsible for the organization of the emergency rescue. The radiation oncologist in charge informs himself about the necessary emergency measures before starting the treatment and carries out the emergency rescue. If the physicist diagnoses a failure in the retraction of the source he tries to remove the failure. If he doesn't succeed in retracting the source the radiation oncologist carries out the rescue of the patient. The organizational structure of the clinic allowing, the emergency physician should invariably be the physician who placed the applicator. In the emergency rescue the radiation oncologist should be protected by a lead barrier (Figure 1, Table 2) and use manipulators (Figure 1). DOSE ASSESSMENT IN PERSONNEL AND PATIENT: The radiation exposure of the rescue personnel is calculated from the photon-equivalence dose HX with the help of the dose-rate constant of 192Ir (Table 3). According to the same procedure there can be evaluated the local radiation exposure of the patient concerned (Table 3). CONCLUSIONS: Generally speaking, all considerations regarding the topic of emergency rescue should always start out from a worst-case scenario. Of all the people involved the patient is the one who is most exposed if the radiation source is located inside his or her body. If an emergency rescue is necessary the radiation exposure of patient and personnel can only be minimized by a quick rescue. This end requires a properly equipped emergency workplace, good training of all the people concerned, and regular exercises of the rescue procedures. A well-practiced emergency management can be of life-saving importance for the patient.

A diamond detector in the dosimetry of high-energy electron and photon beams.

A diamond detector type 60003 (PTW Freiburg) was examined for the purpose of dosimetry with 4-20 MeV electron beams and 4-25 MV photon beams. Results were compared with those obtained by using a Markus chamber for electron beams and an ionization chamber for photon beams. Dose distributions were measured in a water phantom with the detector connected to a Unidos electrometer (PTW Freiburg). After a pre-irradiation of about 5 Gy the diamond detector shows a stability in response which is better than that of an ionization chamber. The current of the diamond detector was measured under variation of photon beam dose rate between 0.1 and 7 Gy min(-1). Different FSDs were chosen. Furthermore the pulse repetition frequency and the depth of the detector were changed. The electron beam dose rate was varied between 0.23 and 4.6 Gy min(-1) by changing the pulse-repetition frequency. The response shows no energy dependence within the covered photon-beam energy range. Between 4 MeV and 18 MeV electron beam energy it shows only a small energy dependence of about 2%, as expected from theory. For smaller electron energies the response increases significantly and an influence of the contact material used for the diamond detector can be surmised. A slight sublinearity of the current and dose rate was found. Detector current and dose rate are related by the expression i alpha Ddelta, where i is the detector current, D is the dose rate and delta is a correction factor of approximately 0.963. Depth-dose curves of photon beams, measured with the diamond detector, show a slight overestimation compared with measurements with the ionization chamber. This overestimation is compensated for by the above correction term. The superior spatial resolution of the diamond detector leads to minor deviations between depth-dose curves of electron beams measured with a Markus chamber and a diamond detector.

[Gamma knife versus stereotactic linear accelerator. Utilization, clinical results and cost-benefit relations]. / Gamma-knife versus stereotaktische Linearbeschleunigerbestrahlung. Durchführung, klinische Ergebnisse und Kosten-Nutzen-Relation.

INTRODUCTION: The principles of radiosurgery were developed in 1951 by Leksell. Their technical realization led to the development of the gamma knife and stereotactically modified linear accelerator. METHODS: In addition to the gamma knife, we present the different principles of convergent beam irradiation (radiosurgery with linear accelerator), the further development to fractionated stereotactic conformal radiotherapy, and the necessary quality-assurance steps. RESULTS: The greatest uncertainties in the precision of radiosurgery result from medical imaging (CT 0.7 x 0.7 x 1 mm; DSA 1-5 mm; MR angiography < 2 mm). The focusing accuracy of the gamma knife (+/- 0.3 mm) can also be achieved today by linear accelerators using a stereotactic floorstand. For the same indication and the same dosage for the target volume, there are no clinical differences between the gamma knife and the linear accelerator (AVM: 80% complete obliteration; metastases: 85% local tumor control; AN: 90% tumor control). However, there are greater differences in costs. There is no constellation where the gamma knife is just as expensive or more cost-effective than the linear accelerator treatment. The most cost-effective solution is modification of an available linear accelerator, resulting in treatment costs per patient of 9,201.25 DM (50 patients/year). CONCLUSION: There seem to be no methodological, physical, clinical or cost reasons for using a gamma knife, especially because the trend is going towards fractionated conformation radiotherapy instead of the application of high single doses.

Fast algorithms for computing and displaying dose-distributions in tomogram-oriented brachy-radiotherapy.

This paper describes in detail a dose calculation algorithm tailored to the needs of tomogram-oriented brachy-radiotherapy and a general-purpose dose visualization for displaying the dose distribution as isolines (or rather interval planes). The verbal description of the algorithms is accompanied by structograms. However, the intention of the authors is to present very fast algorithms that are easy to implement and to give a ready-to-use example formulated in 68020 assembler code. Execution times are estimated theoretically by counting clock cycles and practically by measuring the execution time of sample calculations. It turns out that both the dose calculation as well as the visualization algorithm need less than 1 s when applied to a radioactive point source lying on an arbitrary 320 x 256 grid of three-dimensional space.

Intuitive user interfaces (IUI): a CASE starting point for design and programming.

The acceptance of a software product depends to a considerable extent on the user interface. The class of graphic-oriented user interfaces that are called Intuitive User Interfaces (IUI) is described. These interfaces allow the user to learn to operate software programs quickly. In the following the graphical layout put to use in an IUI is elaborated. All images the layout consists of are created with the aid of a paint program. Using these images, a procedure for creating, programming and linking an IUI to software applications is discussed and recommendations are made concerning software and hardware demands for easily creating IUIs. Practical experience of the authors with this procedure, mainly in the medical area, is described.

A Rexx-controlled developing environment for implementing intuitive user interfaces (IUI).

In [our companion paper] intuitive user interfaces as well as a method for developing and programming such interfaces have been described. The present article will improve and simplify this mode of action. The main tool for this undertaking is the programming and script language Rexx. Using Rexx, all software components described in [the companion paper] are linked to form a developing environment, which acts like an integrated software package. Moreover, with the aid of Rexx, source-code and data structure generation is greatly extended, further decreasing the expenditure of programming intuitive user interfaces. This paper first gives a brief introduction to Rexx. A description of the Rexx-controlled developing environment then follows. Finally, there are elucidated the details of the question of how each single software component is linked to the environment using Rexx.

[The value of NMR tomography in the planning of HDR-afterloading brachytherapy in cervical carcinomas. The experiences with 41 patients]. / Wert der Kernspintomographie zur Planung der HDR-Afterloading-Brachytherapie bei Zervixkarzinomen. Erfahrungen bei 41 Patientinnen.

In 41 patients with inoperable cervical carcinomas, afterloading brachytherapy was used in combination with radiotherapy after planning with MRI (1.5 T spin echo multislice technique). In 27 women, phantoms neutral to MRI were introduced into the uterus to create a topographic situation comparable to that during brachytherapy; at the same time, the position of the applicators was marked. Under the circumstances, MRI demonstrated the position of the uterus and the tumour, the vagina, the bladder, the rectosigmoid and the applicator phantoms in every case. In 88% it was possible to demonstrate the margin of the tumour and normal myometrium. In 18% of the patients, the technique lead to a significant and, in a further 30%, to a marginal improvement in brachytherapy technique.

[2 years' experience with a monitoring and recording system for gynecological afterloading irradiation]. / Zwei Jahre Erfahrung mit einem Uberwachungs- und Protokollierungssystem für gynäkologische Afterloading-Bestrahlungen.

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.

[The use of absorbers to optimize the surface dosage in treatment using ultrahard x-rays]. / Der Einsatz von Absorbern zur Optimierung der Oberflächendosis bei der Therapie mit ultraharten Röntgenstrahlen.

The surface dose in megavoltage x-ray therapy can be modified using two different techniques: either varying the thickness of an absorber positioned directly on the surface of the patient or varying the distance to the surface of an absorber with constant thickness. Surface dose as a function of distance and absorber thickness has been measured at 4 MV and 8 MV x-rays. Both methods yield sufficiently and well-defined dose enhancements at the surface of the patient as desired clinically. The variation of the absorber-surface distance however has been proved to be the more simple and practicable method, offering the additional advantage of no contacting the patients skin.

[Correlation of blood pressure and cadmium and lead content of the hair in nonsmoking males]. / Untersuchungen zum Zusammenhang zwischen dem Blutdruck und dem Cadmium- und Bleigehalt in den Haaren nichtrauchender Männer.

In developed countries, hypertension represents one of the most frequent diseases and is one of the most important risk factors of arteriosclerotic vascular disease e.g. to myocardial infarction or cerebral apoplexy. The etiology of hypertension is unknown in about 90% of cases. The heavy metals cadmium and lead occur in increasing amounts in the human environment. Numerous epidemiological studies and investigations using experimental animals have dealt with the putative relationship between cadmium and lead, and hypertension. The results to date have been quite controversial; thus the issue appears to be unresolved at present. In the present study scalp hair samples were collected from 100 non-smoking 30-to-50-year-old men. After washing, the samples were digested with a mixture of nitric and sulfuric acid in a teflon bomb and analyzed by flameless atomic absorption spectroscopy. For 90% of the test persons the cadmium hair values were in the range of 0 to 1400 micrograms/kg; the corresponding range for hair lead was 0 to 13,000 micrograms/kg. Correlation with diastolic or systolic blood pressure was neither found for cadmium or lead. The test persons with the highest cadmium or lead load were not hypertensive. Some factors should be considered when comparing the present results with those of other investigators reporting a positive correlation in the question under consideration. 1. Previous studies in man frequently did not sufficiently take smoking habits into account. This is essential, however, because, in addition to cadmium and lead, nicotine and carbon monoxide are also constituents of tobacco smoke and contribute to an increase in blood pressure. 2. Previous investigations generally employed blood samples, which is disadvantageous in comparison with the analysis of hair because blood samples do not reflect long-term exposition, which is important in the etiology of chronic diseases. Correlation between hypertension and levels of long-term cadmium and lead exposure in man seem to be unlikely in light of the present results. Nevertheless, numerous potential effects should be considered to obtain further insight in the complex pathogenesis of hypertension.

[Experimental studies of the scatter behavior of fast electrons in the use of electron applicators in radiotherapy]. / Experimentelle Untersuchungen zum Streuverhalten schneller Elektronen bei der Anwendung von Elektronenapplikatoren in der Strahlentherapie.

When using high energy electrons in radiotherapy, there is frequently undesirable electron scatter, which is derived from the applicators used to delimit the field. In order to improve our understanding of the factors which influence scatter, this was studied using fast electrons and a variety of materials to reduce this scatter. The geometry and angulation of the scattering plate and the electron energies were varied during these experiments.

[Possibilities and limits of practice-oriented daily control measurements of linear accelerators]. / Möglichkeiten und Grenzen praxisorientierter täglicher Kontrollmessungen an Linearbeschleunigern.

Daily control measurements of the dose taken at a linear accelerator are described in order to present a practice-oriented measurement and evaluation method rendering possible a long-term quality control. This method allows to establish sudden parameter variations as well as to determine in a simple and precise manner long-term drifting effects with an amplitude within the range of measurement variations and a period of many months. During the time of six months, not only a drifting effect with a long period and an amplitude within the range of pro mille, but also a variation coefficient smaller than 0,3% could be determined.

[Optimization of the isodosis in case of radiotherapy with asymmetric target volumes]. / Optimierung des Isodosenverlaufes bei der Strahlentherapie asymmetrischer Zielvolumina.

By superimposing only two moving fields, it is nearly always possible to adapt an 80% isodose to asymmetric target volumes. By means of wedge filters, it is possible to create asymmetric 80% isodoses with only one irradiation field. The authors compare four different moving field techniques for the irradiation of the left kidney region with regard to the radiation exposure of various transverse body regions. If wedge filters are used for moving field therapy, the average dose values of the different organs are generally significantly inferior to those measured in case of conventional moving field therapy. The reduction of the total volume exposure by 20% and of the liver exposure by nearly 50% is most favorable. Another great advantage is the complete sparing of the remaining kidney. These quantitative advantages are supplemented by the qualitative factor concerning the considerably simplified therapy planning and the easy focussing.