No abstract

The guideline contains recommendations for hyperthermia treatments, including indication, preparation, treatment, and standardized analysis.

It has been shown from an evaluation of the inverse reading of the dosemeter (1/M) against the inverse of the polarizing voltage (1/V), obtained with a number of commercially available ionization chambers, using dose per pulse values between 0.16 and 5 mGy, that a linear relationship between the recombination correction factor kS and dose per pulse (DPP) can be found. At dose per pulse values above 1 mGy the method of a general equation with coefficients dependent on the chamber type gives more accurate results than the Boag method. This method was already proposed by Burns and McEwen (1998, Phys. Med. Biol. 43 2033) and avoids comprehensive and time-consuming measurements of Jaffé plots which are a prerequisite for the application of the multi-voltage analysis (MVA) or the two-voltage analysis (TVA). We evaluated and verified the response of ionization chambers on the recombination effect in pulsed accelerator beams for both photons and electrons. Our main conclusions are: (1) The correction factor k(S) depends only on the DPP and the chamber type. There is no influence of radiation type and energy. (2) For all the chambers investigated there is a linear relationship between kS and DPP up to 5 mGy/pulse, and for two chambers we could show linearity up to 40 mGy/pulse. (3) A general formalism, such as that of Boag, characterizes chambers exclusively by the distance of the electrodes and gives a trend for the correction factor, and therefore (4) a general formalism has to reflect the influence of the chamber construction on the recombination by the introduction of chamber-type dependent coefficients.

No abstract

The hyperthermia effect is based on its thermal influence on tumours. Therefore a controlled heating of the tumours must be achieved. In order to guarantee this, two points must be fulfilled at least: First, the hyperthermia equipment must have the necessary power and steering capability. Second, the distribution of the 'hyperthermic drug', the heat, has to be measured and controlled over the whole treatment time. To reach this aim both a sophisticated technique and a staff trained in hyperthermia are required. In treating patients such as those with cervical cancer, the volume to be exposed and the dosage must be clarified. This means that very special technical and medical conditions must be fulfilled in hyperthermia. To reach and maintain a certain level of quality, hyperthermia is embedded in a framework of procedures. These procedures are defined in the modules of quality management. Therefore quality management must contain specific guidelines for each application, i.e. coordinated standards have to be defined. When adapting these standards in hyperthermia, comparable and comprehensible results of the treatment are guaranteed. Furthermore, an analysis of the treatments under a scientific point of view will be possible and finally result in improvements of this method.

Purpose: Rotational IMRT is a new technique, whose value still has to be assessed. We evaluated its adequacy for the treatment of head and neck (H&N) cancer compared to the well-established step-and-shoot IMRT. Materials and Methods: A total of 15 patients, who were treated with either IMRT (13 patients) or VMAT (2 patients) in the H&N region, were chosen. For each patient, a treatment plan with the respective other technique was calculated. To compare the resulting dose distributions, the dose-volume histograms (DVHs) were evaluated. To quantify the differences, a new quality index (QI) was introduced, as a measure of the planning target volume (PTV) coverage and homogeneity. A conformity function (CF) was defined to estimate normal tissue sparing. Results:The QI for VMAT amounts to 36.3, whereas for IMRT the mean value is 66.5, indicating better PTV coverage as well as less overdosage for the rotational technique. While the sparing of organs at risk (OAR) was similar for both techniques, the CF shows a significantly better sparing of healthy tissue for all doses with VMAT treatment. Conclusions: VMAT results in dose distributions for H&N patients that are at least comparable with treatments performed with step-and-shoot IMRT. Two new tools to quantify the quality of dose distributions are presented and have proven to be useful. VMAT und Step&Shoot-IMRT bei Kopf-Hals-Tumor-Patienten: Eine vergleichende AnalyseZielsetzung: Rotationsbestrahlung mit Intensitätsmodulierung ist eine neue Technik, deren Wert erst noch beurteilt werden muss. Wir untersuchten deren Eignung für die Behandlung von Kopf-Hals-(H&N-)Tumoren im Vergleich zu etablierter Step&Shoot-IMRT. Material und Methoden: Es wurden 15 Patienten ausgewählt, die mit IMRT (13 Patienten) oder VMAT (2 Patienten) in der H&N-Region behandelt wurden. Für jeden wurde ein Bestrahlungsplan mit der jeweils anderen Technik berechnet. Um die resultierenden Dosisverteilungen zu vergleichen, wurden Dosis-Volumen Histogramme (DVHs) ausgewertet. Zur Quantifizierung der Unterschiede wurde ein neuer Qualitätsindex (QI) eingeführt, der ein Maß für die Dosisabdeckung und -homogenität innerhalb des PTV ist. Eine Konformitätsfunktion (CF) wurde definiert, um die Nomalgewebeschonung abzuschätzen. Ergebnisse: Der QI für VMAT beträgt 36,3, während sich der Mittelwert für IMRT auf 66,5 beläuft, was eine bessere Dosisabdeckung und -homogenität bei der Rotationsbestrahlung anzeigt. Die Schonung der Risikoorgane war für beide Techniken ähnlich; der CF zeigte eine deutlich bessere Normalgewebeschonung für VMAT bei allen Dosiswerten. Schlussfolgerung: VMAT erlaubt für die Behandlung von H&N-Patienten Dosisverteilungen zu erzeugen, die mindestens vergleichbar sind mit denen, die mit Step&Shoot-IMRT machbar sind. Zwei neue Größen zur Quantifizierung der Qualität von Dosisverteilungen wurden präsentiert und deren Nutzen gezeigt. Schlüsselwörter: IMRT • IMAT • VMAT • RapidArc • Kopf-Hals-Krebs • Konformitätsindex • Normalgewebeschonung Wiehle R, et al. VMAT vs ssIMRT in H&N Cancer

Current dosimetry protocols from AAPM, DIN and IAEA recommend a cross-calibration for plane-parallel chambers against a calibrated thimble chamber for electron dosimetry. The rationale for this is the assumed chamber-to-chamber variation of plane-parallel chambers and the large uncertainty in the wall perturbation factor (p(wall)60Co)pp at 60Co for plane-parallel chambers. We have confirmed the results of other authors that chamber-to-chamber variation of the investigated chambers of types Roos, Markus, Advanced Markus and Farmer is less than 0.3%. Starting with a calibration factor for absorbed dose to water and on the basis of the three dosimetry protocols AAPM TG-51, DIN 6800-2 (slightly modified) and IAEA TRS-398, values for (p(wall)60Co)Roos of 1.024 +/- 0.005, (p(wall)60Co)Markus of 1.016 +/- 0.005 and (p(wall)60Co)Advanced Markus of 1.014 +/- 0.005 have been determined. In future this will permit electron dosimetry with the above-listed plane-parallel chambers having a calibration factor N(D, w)60Co without the necessity for cross-calibration against a thimble chamber.

The dosimetry protocols DIN 6800-2 and AAPM TG-51, both based on the absorbed dose to water concept, are compared in their theoretical background and in their application to electron dosimetry. The agreement and disagreement in correction factors and energy parameters used in both protocols will be shown and discussed. Measurements with three different types of ionization chambers were performed and evaluated according to both protocols. As a result the perturbation correction factor P(60Co)wall for the Roos chamber was determined to 1.024 +/- 0.5%.