Determination of field size limitations in stereotactic and intensity modulated radiotherapy.

For dose measurement in small photon fields, different detectors are currently in use: TLD, semiconductor, diamond-detector, film, etc. But for absolute dosimetry, ionization chambers show the most advantages. To meet the basic dosimetrical requirements for lateral electron equilibrium the field size F must not remain under specified values: i.e. 5.2 x 5.2 cm2 for 15 MeV X-bremsstrahlung. As well as increasing the focus-chamber-distance, changing the physical density of the build-up material in the close vicinity of the chamber will be helpful to determine the output factor OF for smaller fields. By means of a correction factor, k(mat), this is taken into account. For a 6 MeV X and a 15 MeV X-bremsstrahlung of linear accelerators the lower limit of the field size F is determined: F > or = 0.8 cm. This value is mainly dependent on the diameter of the focal-spot (phi = 3 mm) of the treatment unit including design characteristics of the treatment head. Beside the dosimetrical aspects, some geometrical parameters have to be considered, when accuracy of dose application should remain on the same level as in medium and large field treatment (4 cm < or = F < or = F(max)). To keep dose-volume errors as low as +/- 10 % (diameter of PTV: 20 mm), the mean total error delta of CT-scanning (delta(p)), planning (delta(pl)), patient positioning (delta(x)), and treatment unit instabilities (delta(m)) should not exceed +/- 0.8 mm.

[How tolerant are partial dose values? Some additional remarks on the concept of a tolerance dose]. / Wie tolerant sind Partialdosiswerte? Einige ergänzende Bemerkungen zu dem Konzept der Toleranzdosis.

By means of the NSD formula and its modifications (CRE, TDF) evaluated from radiotherapy experience by Ellis, it is possible to estimate the acceptance of applied radiotherapy and fractionation scheme. Because the parameters of the Ellis formula are calculated from patients data, they show a dispersion as usually in biological systems. These dispersions are considered as entrance error. In mathematical transformations errors are multiplied according to the principle of superposition of errors. Especially when judging tolerance values of organs of risk the dispersion is quite important. The problem of dispersion of resulting partial tolerance values is demonstrated by some examples of clinical cases.

Mastomys natalensis or Mastomys coucha. Correct species designation in animal experiments.

Haemoglobin electrophoresis and chromosome analysis indicate that the widely used multimammate rat (chamois coloured) as experimental animal belongs to the species Mastomys coucha (Smith, 1836) and not, as commonly assumed, to Mastomys natalensis (Smith, 1834).

[The effect of the focal distance parameter on the dose rate of radiotherapy equipment]. / Uber den Einfluss des Abstandsparameters auf die Dosisleistung von Strahlentherapiegeräten.

In radiotherapy it is sometimes necessary to use nonstandard treatment distances, i.e. in mantle-field irradiation or in total-body irradiation. The design of the collimating system as well as other components of the treatment head are influencing the dose rate depending on focus-patient respectively focus-phantom distance (FPD). The quality of the collimator and the dependence on FPD, which deviates from the inverse-square law, were described by a new defined parameter INV. This parameter INV was checked experimentally on various treatment units. For approximation and explanation of this INV factor a combination of a point, line and area source is proposed.

[Hyperfractionation--a new challenge for medical electron linear accelerators?]. / Hyperfraktionierung--eine neue Herausforderung an medizinische Elektronenlinearbeschleuniger?

In radiotherapy to an increasingly degree radiobiological aspects of the tumor behaviour during therapy are realized in daily routine. An example for this is the so called hyperfractionation of the total dose: that means multiple small fractions are applied. Doses of as low as circa 40 cGy per field are necessary. This investigation affects the constancy and the behaviour of the following beam parameters of various treatment units during the initial stage of operation (circa ten seconds): energy of bremsstrahlung, symmetry, flatness and proportionality of dose.

[New investigations about the activation of air by the 42-Mev continuous radiation of a betatron (author's transl)]. / Neue Untersuchungen zur Luftaktivierung durch die 42-MeV-Bremsstrahlung eines Betatrons.

Measurements of the activity of urea are a simple and reproducible method to determine the activation of air produced by the continuous radiation of a medically used accelerator [3,4]. The authors studied the activity produced by photonuclear induction using a 42 MeV betatron under unfavorable irradiation conditions. The activity measured per individual irradiation is 1.56 x 10(5) Bq 13N and 4.93 x 10(5) Bq 15O. The limit values indicated in the Radioprotection Regulation are not reached if an intensive air exchange and a waiting-time between the end of the irradiation and the entering of the irradiation room is guaranteed.

[Measurement and calculation of the air activation caused by 15 MeV continuous radiation emitted by a linear accelerator (author's transl)]. / Messung und Berechnung der Luftaktivierung durch die 15-MeV-Bremsstrahlung eines Linearbeschleunigers.

The rate of air activation caused by the 15 MeV continuous radiation of a "Clinac 20" can be concluded from activation measurements in urea tablets. In case of the most unfavourable irradiation conditions, a maximum field size of 35 X 35 cm2, and a distance focus-wall of 450 cm, an air activation of 6, 18 X 10(4) Bq per individual irradiation is calculated. The limit of activity concentration prescribed by the Strahlenschutzverordnung (radioprotection directive) is not reached if a sufficient change of air is guaranteed. This method of measuring the air activation is simple, not time-consuming and can be effected with a high degree of accuracy. Measurements and calculations are compared.

[The low-pass filtering of scintigraphic picture data in myocardial scintigraphy (author's transl)]. / Die Tiefpassfilterung von szintigraphischen Bilddaten am Beispiel der Myokardszintigraphie.

A digital Gauss-type filter is treated in consideration of low count dynamic myocardial scintigraphy. This filter type is favourable for several reasons. It is neutral in phase. An increase of signal-to-noise ratio in the scintigram is possible with tolerable loss of resolution. A nearly constant signal-to-noise ratio is available with a count controlled filtering. The estimation of the required count rate for a desired resolution is possible. The scintigraphic pulse height can be matched to the image processing system at all times. Fixed collimator dependent filter routines can be integrated into the image processing software.

[Practical application of optimization criteria for geometrical distributions of the radiation dose: choice of the irradiation technique in 60Co-teletherapy (author's transl)]. / Praktische Anwendung der Optimierungskriterien für geometrische Strahlendosisverteilungen. Wahl der Bestrahlungstechik bei Co-60.

Fifty-four usual cases of radiation therapy were evaluated, comparing the effective surface doses in sound tissues for different irradiation techniques. Irradiation of the esophagus, mediastinum, lung and bladder was calculated for the cross-fire method, 3-field therapy, and monaxial or biaxial pendulum technique. Pendulum irradiation proved superior to multiple-field techniques in all cases. The number of free parameters in computer-assisted relative optimization of dose distributions can be reduced by means of the determination of the irradiation technique.

[An analytical method for calculation of electron dose distributions. Part II: Experimental verification and application in coplanar irradiation techniques (author's transl)]. / Ein analytisches Verfahren zur Berechnung von Elektronendosisverteilungen. Teil II: Experimentelle Uberprüfung und Anwendung bei koplanaren Bestrahlungsmethoden.

The analytical method for calculation of electron dose distributions described in part I was experimentally verified using a 42-MeV betatron. For this, a comparison was made between the calculated and the measured dose distributions obtained with a homogeneous or inhomogeneous water or polystyrol phantom with plane or with uneven surfaces, the inhomogeneities consisting in cavities and cork intercalations. Thus, the accuracy of the algorithm and of the consideration for inhomogeneities and irregular surfaces is demonstrated, and limitations of the method's applicability are shown. Some examples of calculated dose distributions in coplanar irradiation techniques using solely electron beams or else a combined treatment with photons and electrons are exhibiting the particular bearing of electronic data processing on the treatment planning in depth therapy with electrons in the energy range above 20 MeV.

[An analytical method to calculate electron dose distributions. Part I: Method (author's transl)]. / Ein analytisches Verfahren zur Berechnung von Elektronendosisverteilungen. Teil I: Das Verfahren.

A method for the calculation of electron dose distributions is described. The dose distributions of stationary electron beams in water are represented by formulas for depth dose curves and transverse distributions. Curved surfaces, oblique incidence of rays, and inhomogeneities are taken into account by applying the law of distance and the method of equivalent thicknesses of water layers. A detailed program is given to calculate the electron dose distributions in that plane of the central ray which is at right angle to the theoretical circle plane of a 42 MeV betatron.

[Evaluation of isotope nephrograms by the deconvolution method (author's transl)]. / Auswertung von Isotopennephrogrammen durch die Entfaltungsmethode.

By means of deconvolution, which can be preformed simply with a minicomputer, a new function is derived from the circulation activity time function and the renal activity time function. This function describes the impulse response of the system "Kidney". The activity time functions are determined with a four-probe counter. The impulse response allows statements about the time during which the activity remains in the kidney, the relative blood flow of both kidneys and a so-called passage time distribution. It was also attempted to substitute the circulation activity time function by a derivative of the bladder activity time function.

[Changes of the depth dose curve in case of 42 MeV photon irradiation through a plexiglass plate of 3 cm (author's transl)]. / Anderung des Tiefendosisverlaufes bei 42-MeV-Photonen-Bestrahlung durch eine 3 cm dicke Plexiglasplatte.

The authors give curves for the photon radiation of a 42 MeV betatron valid for different field sizes with a distance focus-surface of 120 cm. These curves allow to calculate the dose of the central ray for an irradiation in the compression chamber "Oxyfulm".

Product inhibition of the fermentative formation of glutamic acid.

The addition of penicillin to cells of Corynebacterium glutamicum growing in 5-liter fermentors initiated the excretion of glutamic acid. The rate of glutamate production in fermentors declined continuously with time and reached 75% of the initial rate in 24 hr after penicillin had been added. The addition of glutamate to resting cell suspensions had only a slight effect on sugar utilization but caused a marked decrease in glutamate excretion. It is suggested that the high level of glutamate accumulating in the fermentation broth is responsible for inhibiting its own production.

Glucose-6-phosphate dehydrogenase and its deficiency in mutants of Corynebacterium glutamicum.

Corynebacterium glutamicum is a member of a group of taxonomically related glutamate-excreting bacteria which utilize glucose both by the Embden-Meyerhof and the pentose phosphate pathways, the latter sequence accounting for 10 to 38% of the glucose metabolized. Some of the properties of glucose-6-phosphate dehydrogenase in crude extracts of C. glutamicum were studied. The enzyme was rapidly inactivated by dilution in tris (hydroxymethyl)aminomethane-hydrochloride buffer. This inactivation was prevented by the presence of 0.45 m NaCl. Mg(++) was required for enzyme activity, but Mn(++), Ca(++), Sr(++), and Ba(++) were equally effective. Growth of the organism under differing conditions did not markedly affect the specific activity of the enzyme. A generally applicable method for detecting colonies deficient in glucose-6-phosphate dehydrogenase was developed. Mutants so obtained were found to be auxotrophic for tryptophan. Upon reversion of the tryptophan requirement, the revertants still retained the property of glucose-6-phosphate dehydrogenase deficiency. Neither the mutants nor the revertants could grow as rapidly as the parent culture in glucose, in gluconate, or in a complex medium.