The new NACP- and ICRU-dosimetry protocols for dosimetry of high-energy photon and electron radiation.
Explore the source record for details and available documents.
Cobalt Radioisotopes↗
Biomedical subjects
H Svensson
Publications and source records attributed to H Svensson.
Detecting arterial and venous obstruction in flaps.
Island skin flaps based on the latissimus dorsi muscle were raised in domestic pigs. Flap circulation, maintained only by the vascular pedicle, was monitored by laser Doppler flowmetry, laser photometry, and transcutaneously measured carbon dioxide tension. Both arterial and venous occlusion were accompanied by very low laser Doppler flow values. In laser photometry, the backscattered intensity of light remained unchanged or was slightly increased during arterial occlusion. In response to venous occlusion, however, the light intensity decreased markedly. Transcutaneous carbon dioxide tension increased in both venous and arterial occlusion. When venous outflow pressure was raised incrementally, both the laser Doppler flow value and the total backscattered light intensity fell proportionately. Laser Doppler flowmetry might thus be useful clinically to detect decreased blood flow in transferred flaps, and laser photometry may determine if the decreased flow is related to the arterial or venous side.
Animals↗
Detecting changes of arterial and venous blood flow in flaps.
Island skin flaps based on the latissimus dorsi muscle were raised in domestic pigs. Simultaneous recordings of laser Doppler flowmetric and laser photometric values were made on the skin in the middle of the flap. Occlusion of either the artery or the vein of the pedicle was accompanied by very low laser Doppler flow values. In laser photometry the total intensity of backscattered light remained unchanged or was sightly increased during arterial occlusion. In response to venous occlusion, however, it decreased markedly. As venous outflow pressure was increased step by step, both the laser Doppler flow value and the laser photometry value fell proportionally; thus, the greater the increase in pressure the lower were the steady state levels of both variables. Stepwise reductions of arterial inflow pressure were followed by proportional decreases in both mean blood volume flow, recorded using electromagnetic flowmetry, and in laser Doppler flowmetric values. However, laser photometric values varied only minimally. Laser Doppler flowmetry thus might be a useful clinical aid in detecting decreased blood flow in transferred flaps, and laser photometry may determine whether the decreased flow is due to arterial or venous causes.
Animals↗
Influence of the bacterial flora of the gut on sulfur amino acid degradation. A study of patients with bacterial overgrowth before and during treatment with oxytetracycline or metronidazole.
The urinary excretion of sulfur amino acids and their main degradation products was determined in 10 patients with bacterial overgrowth during treatment with oxytetracycline or metronidazole. A normal excretion of total sulfur and inorganic sulfate was found during treatment with both antibiotics, indicating a normal intake, uptake, and oxidation of sulfur amino acids to inorganic sulfate. Irrespective of type of antibiotic given, a normalization of the increased ester sulfate excretion was found, favoring the opinion that both the aerobic and anaerobic flora of the gut contribute to the formation of sulfate esters. The cystathioninuria found in patients with bacterial overgrowth was normalized only by treatment with metronidazole. Both antibiotics resulted in a reduced excretion of taurine and thiosulfate, but especially for thiosulfate, the effect of metronidazole treatment was more pronounced. The results suggest that the bacterial flora of the gut, such as anaerobes, may be of importance in the formation of thiosulfate in the human body.
Adult↗
Laser Doppler flowmetry and laser photometry for monitoring free flaps.
A device based on the laser Doppler perfusion meter, "Periflux", was constructed for continuous post-operative monitoring of the circulation of free flaps. It was evaluated in 17 consecutive clinical free flaps, four of which were beset by circulatory complications. In all 17 cases the device provided reliable and readily accessible information concerning the state of flap blood flow.
Humans↗
Quality assurance in radiation therapy: physical aspects.
The present status of the quality assurance work regarding the physical aspects in radiation treatments is discussed. In particular, the situation in Europe is surveyed. An analysis of the errors in the delivered absorbed dose to a specified point in the irradiated patient shows that the uncertainty, to approximately the same degree, depends on the dose distribution determination, the dose planning and the patient irradiation. Following the procedure generally in use, the overall uncertainty will be about 8%. The random uncertainties are estimated as one standard deviation and non-random uncertainties to corresponding degree of uncertainty. It is argued that this level must be improved. Furthermore, dose intercomparisons show that in reality much larger errors occur in clinical practice. Different means to improve this situation are discussed.
Calibration↗
Charge build-up effects in insulating phantom materials.
When a medium is irradiated with electrons, electric charges are injected into the medium. If this is an electric insulator and its extension in the beam direction is larger than the electron range, the electrons are trapped inside the medium. In this work the influence on the ionization chamber dosimetry of the charge trapping in insulating phantom materials, such as polystyrene and polymethylmethacrylate (PMMA), has been investigated. It has been shown that the electron fluence inside a cylindric ionization chamber used in these materials increases when the number of electrons trapped in the phantom increases. The influence of various parameters, such as electron energy, accumulated absorbed dose, type and purity of the phantom material, radiation induced conductivity and ionization chamber construction are discussed. The effect can cause errors of several per cent in the dosimetry. We conclude, in agreement with the conclusion of GALBRAITH et coll., that insulating phantom materials should therefore be avoided in electron beam dosimetry.
Electricity↗
Laser Doppler flowmetry and transcutaneously measured carbon dioxide tension for observing changes of skin blood flow in fingers.
Laser Doppler flowmetry (LDF) and transcutaneous carbon dioxide tension measurements (PtcCO2) were performed on fingers of healthy volunteers subjected to a sequence of hydrostatic and thermal stimuli. LDF response using an unheated probe agreed well with measurements made with Xenon133 clearance and strain gauge plethysmography in a previous work. The PtcCO2 results, however, were found not in any way to reflect changes in skin blood flow.
Adult↗
[Protracted QT--review and case reports].
Explore the source record for details and available documents.
Adolescent↗
Dosimetric intercomparison at the Scandinavian radiation therapy centres. I. Absorbed dose intercomparison.
A dosimetric intercomparison was carried out at all the centres in Denmark, Norway and Sweden. All the beam qualities (except conventional roentgen rays) used in radiation therapy were investigated. The ratio of the absorbed dose measured by us to that stated by the centre was determined. The mean ratio and standard deviation with the reference field-size were for 60Co gamma beams 1.001 +/- 0.014, for roentgen ray beams (4-45 MV) 1.017 +/- 0.023, electron beams with energy E0 less than 10 MeV 0.989 +/- 0.027, and electron beams with energy E0 greater than or equal to 10 MeV 0.996 +/- 0.034. The difference between the highest and lowest ratios was 17.8 per cent. A systematic difference due to the application of different protocols (NACP 1972 and 1980) was found.
Denmark↗
Ferrous sulphate dosimeter for control of ionization chamber dosimetry of electron and 60Co gamma beams.
A check of the dosimetry using ionization chambers and applying the procedures described in the Nordic dosimetry protocols (NACP 1980, 1981) was carried out using the ferrous sulphate dosimeter as reference. Measurements have been carried out in electron beams in the energy range 2.8 to 27.5 MeV and in 60Co gamma beams. Consistent results were obtained with the two systems within about one per cent. Larger differences were only observed in electron beams containing a large proportion of scattered low energy electrons and contaminating roentgen rays which were not corrected for in the ionization chamber method.
Cobalt Radioisotopes↗
Liquid ionization chamber for absorbed dose determinations in photon and electron beams.
The use of a liquid ionization chamber for measurements in electron and photon beams with energies above 1 MeV has been investigated. The liquid in the chamber is 2,2,4-trimethylpentane. Fundamental properties such as the reproducibility of the measured charge per absorbed dose, the temperature dependence, and the angular dependence have been experimentally analysed. The general recombination losses in pulsed beams are shown to be dependent on the transport time of the ions in the liquid. For a longer transport time than the time between two consecutive pulses the losses depend on the mean dose rate and for a shorter transport time the losses depend on the absorbed dose per pulse. The Jaffe method is used for determination of the initial recombination losses, and compared with results from other authors. The chamber is particularly useful for absorbed dose determination in electron beams since the relation between measured charge and absorbed dose to water is almost energy independent. In photon beams the relation is somewhat quality dependent particularly at qualities below 10 MV. The change of the free ion yield caused by the small change of mean LET with the quality of the photon beam is probably the reason. Procedures for the calibration of the liquid chamber and the absorbed dose determination in electron and photon beams are described.
Electrons↗
Calibration and use of plane-parallel ionization chambers for the determination of absorbed dose in electron beams.
The dosimetry procedures to be used at electron energies, E0, below 15 MeV in order to determine absorbed dose to water with an ionization chamber have been investigated. The performance of different types of plane parallel ionization chambers was tested. A chamber suitable for use in accordance with the Nordic dosimetry recommendations was designed. Correction factors to be applied in order to use solid phantom materials instead of water were determined.
Electrons↗
Investigation of the possibility of using photoneutron beams for radiation therapy.
The possibility has been investigated of using electrons accelerated by a 50 MeV racetrack microtron for generation of photoneutron beams for radiation therapy. Central axis depth-dose curves have been measured in an A-150 tissue-equivalent phantom. Neutron half-value depths between 4.4 and 5.2 g cm-2 were obtained at an SSD of 100 cm for different converter materials and target geometries. At an absorbed dose ratio of 1:1 for neutrons and photons at the dose maximum, the total absorbed dose rates are estimated to be 0.1 Gy min-1 at 100 micronA electron current and a SSD of 100 cm. At a depth of 5 cm the neutron to photon absorbed dose ratio is typically 1:2 and the OER is expected to be about 1.8. Some dose distributional and radiobiological advantages of a physically mixed beam of neutrons and photons for external beam radiation therapy are discussed.
Electrons↗
Electron and photon beams from a 50 MeV racetrack microtron.
The quality of broad high energy photon and electron beams can be improved considerably by the scanning of elementary narrow beams. Dose distributions produced in this way have advantages with respect to improved dose gradients and therapeutic ranges for electrons and lower surface doses, increased depth doses and half value depths for photons. The possibility of giving the whole therapeutic dose in a single local pulse of short duration is discussed as a new method to protect superficial tissues.
Electrons↗
Radiation beam characteristics of a 22 MeV microtron.
The properties of the electron and photon beams from a 22 MeV clinical microton are presented. Favourable isodose distributions for radiation therapy are obtained for both modalities. For the electron beam this is accomplished using a dual scattering foil system in which the secondary foil is shaped to optimize uniformity and minimize energy loss and energy straggling. The photon beam is flattened by a composite filter to produce dose distributions of high uniformity over a wide depth interval.
Electrons↗
Ferrous sulphate dosimetry for electrons. A re-evaluation.
A theory was developed for the perturbation correction to be applied in the calorimetric determination of the ferrous sulphate dosimeter G-value. Recent determinations of the molar extinction coefficient, epsilonm, have shown that systematic errors in epsilon may have influenced experimental G-values. With precision spectrophotometers this error is cancelled in the product epsilonm.G. It was shown that after applying the perturbation correction a very small spread was obtained in calorimetric epsilonm.G-values; the standard error of the mean being 0.2 per cent. The mean G-value is 2.3 per cent lower than that recommended in ICRU Report No. 21.
Absorption↗
Depth absorbed dose distributions for electrons.
Explore the source record for details and available documents.
Electrons↗