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Results of research and development

Pulsed photon radiation

Further information: Problematik bei Messungen in gepulsten Photonen-Strahlungsfeldern.

Contact:
Dr. Oliver Hupe
Phone: +49 (0) 531 592 6310

Literature:

  • Klammer, J., Roth, J., Hupe, O.:
    Novel Reference RadiationFields for Pulsed Phaton Radiation Installed at PTB
    Radiation Protection Dosimetry, Vol. 151 No. 3, pp. 478-482 (2012)
  • ISO/TS 18090-1:2015:
    Radiological protection — Characteristics of reference pulsed radiation — Part 1: Photon radiation
  • IEX/TS 62743:
    Radiation protection instrumentation – Electronic counting dosemeters for pulsed fields of ionizing radiation

Dosisbelastung helfender Personen in der Human-, Zahnmedizin und der Tierheilkunde

Der erste Teilbereich ("Helfende Personen") eines vom Bundesministerium für Umwelt, Naturschutz, Bau und Reaktorsicherheit geförderten Vorhabens beschäftigt sich mit der Dosisermittlung bei helfenden Personen: Die Ermittlung der Körperdosis ist für Personen erforderlich, die sich in Kontrollbereichen aufhalten (§ 40 Abs. 1 Satz 1, § 81 Abs. 5 Satz  Strahlenschutzverordnung und § 25 Abs. 5 Satz 3, § 35 Abs. 1 Satz 1 Röntgenverordnung). Zu diesem Kreis gehören neben den beruflich strahlenexponierten Personen auch die helfenden Personen in der Human- und Zahnmedizin und Personen in der Tierheilkunde, die Tiere während der Untersuchung halten (§ 37 Abs. 1 Satz 1 Nr. 2b StrlSchV, § 22 Abs. 1 Nr. 2b RöV). Die Messungen erfolgten sowohl in der klinischen Praxis als auch unter Laborbedingungen. Hierzu wurde unter anderem ein Katzenphantom als realistischer Streukörper hergestellt.

Ziel der Untersuchungen für diesen Teilbereich war es zu ermitteln, welche Dosis diese Personen bei typischen Untersuchungsszenarien erhalten und wie häufig helfende Personen eingesetzt werden.

Contact:
Dr. Oliver Hupe
Phone: +49 (0) 531 592 6310

Literature:

Röntgen-Personenscanner

Der zweite Teilbereich ("Durchleuchtungseinrichtungen") eines vom Bundesministerium für Umwelt, Naturschutz, Bau und Reaktorsicherheit geförderten Vorhabens bezieht sich auf die Anwendung ionisierender Strahlung für die Kontrolle von LKWs und Personen. Durchleuchtungseinrichtungen mit Röntgenstrahlung kommen international an Grenzen, Flughäfen, Seehäfen, etc. immer häufiger zum Einsatz. Ziel der Untersuchungen dieses Teilbereichs war es, die Orts- und Personendosis-Werte bei kommerziell erhältlichen Anlagen zu bestimmen. Auf Wunsch des A4-Ausschusses der SSK wurden zusätzlich im Rahmen des Vorhabens Dosismessungen an der Container- Durchleuchtungsanlage im Hamburger Hafen durchgeführt.

Contact:
Dr. Oliver Hupe
Phone: +49 (0) 531 592 6310

Literature:

Traceable dosimetry in the radiation field of a miniature X-ray tube for brachytherapy

A new development in brachytherapy is the use of miniature X-ray tubes with a maximum tube voltage of 50 kV (see Figure below) which are directly inserted into the patientxs body. Various types are commercially available and are used in hospitals. At present, miniature X-ray facilities are most frequently used for the intraoperative irradiation of mastocarcinoma. After a surgical excision of the tumour tissue, these tubes are placed in the cavity which has emerged, and the surrounding tissue is irradiated for about 25 minutes to kill tumour cells which might still exist.

The realization of traceable dosimetry for therapy with these X-ray facilities is the object of a research project which is currently being implemented within the scope of the "European Metrology Research Programme" of the European national metrology institutes.

To realize the unit of the absorbed dose rate to water in the radiation field of the miniaturized X-ray tubes, the primary standard for the realization of the absorbed dose rate to water for LDR sources is further developed. To disseminate the dose rate to hospitals, measurement procedures are being elaborated. The aim is to elaborate a standard or a protocol for medical physicists for dosimetry when using miniature X-ray facilities.

Figure: Two different types of miniature X-ray tubes. Left: Intrabeam X-ray facility (Zeiss), right: AXXENT X-ray facility (Xoft).

Traceable dosimetry in clinical fields in brachytherapy

Another current focus of research - also within the scope of the above-mentioned European research project - is dosimetry in clinical fields of brachytherapy using HDR sources. HDR sources are mostly used in hospitals in combination with so-called "applicators". Applicators are auxiliary means for positioning the source in the patient'x body and for shaping the radiation field, for example to shield radiation-sensitive tissue near the tumour from the radiation field and to spare it in this way. The respective applicator type used depends on the tumour geometry and on its location in the body. In the present protocols for clinical dosimetry and in treatment planning systems, the influence of the applicators on the dose applied is not taken into account, see Rivard et al.

The determination of the spatial dose rate distribution in typical clinical radiation fields of HDR brachytherapy (i.e. HDR sources using applicators) with an adequately low measurement uncertainty is a great metrological challenge. For this purpose, a 3D measurement system is under construction with which dose measurements with an uncertainty of only few percent shall be possible. The activities are currently performed in cooperation with the Medizinische Hochschuhle Hannover (MHH).

Literature:

  • Rivard M. J., Coursey B. M., DeWerd L. A., Hanson W. F., Huq M. S., Ibbott G. S., Mitch M. G., Nath R., Williamson J. F.:
    Update of AAPM Task Group No. 43 Report: a revised AAPM protocol for brachytherapy dose calculations.
    Med. Phys. 31. 633–74, 2004

Contact:
Dr. Thorsten Schneider
Phone: +49 (0) 531 592 6346

Experimental determination of the source type-specific Λ-factor in the HDR photon brachytherapy

Within the scope of a European research project, a primary standard was set up for the realization of the absorbed dose rate to water for HDR brachytherapy sources. By means of water calorimetry (WG 6.23 Unit of absorbed dose to water), the absorbed dose rate to water can be determined in the near field of the sources, see Krauss et al. The detector used in the calorimeter (see Figure below) is based on the detector used in water calorimetry for high-energy fields. In order to achieve an exact and reproducible positioning of the source in front of the detector, the source is inserted into a stainless steel needle (inner diameter: 1.35 mm) which can be fixed very precisely in front of the detector at various distances (minimum distance: 24.35 mm), see Krauss et al. From the measurements taken at various distances, the absorbed dose rate to water is determined at a distance of 1 cm from the source.

Figure: Detector element for the water calorimeter to realize the absorbed dose rate to water for HDR brachytherapy sources.

In the case of the calorimetric measurements, the following effect interferes: radioactive HDR sources heat up due to the self-absorption of gamma radiation and/or due to the energy dissipation of the electrons in the source material. The taking into account of this "self-heatx is one of the greatest challenges (besides the steep depth dose distribution in the detector) of the absorbed dose rate to water realization by means of calorimetry.

The direct realization of the absorbed dose rate to water for HDR sources was used to experimentally determine the value of the dose rate constant x and, thus, to verify the calculated values. The values experimentally determined for selected types of 192Ir sources show good agreement with the calculated ones, see Selbach et al.

The realization by means of water calorimetry is experimental and - if a low uncertainty is to be attained - also very time-consuming, which explains why this procedure is not suited for a direct routine calibration of individual sources.

Due to the stability of the value of the dose rate constant, which only depends on the type of the source, the absorbed dose rate to water should, also in future, be disseminated in brachytherapy via the calibration of HDR sources in the unit of RAKR, by using experimentally validated values of the dose rate constant.

Due to the low-energy photon radiation and the low dose rate, the dose rate measurand for LDR sources must be realized and disseminated in another way than for HDR sources.

Literature:

  • Krauss A., Bambynek M., Selbach H.-J.:
    Application of water calorimetry as absorbed dose to water standards for radiotherapy dosimetry.
    Workshop on Absorbed Dose and Air Kerma Primary Standards, Paris, 2007, Proceedings
  • Selbach H.-J., Bambynek M., Aubineau-Laniece I., Gabris F., Guerra A.S., Toni M.P., de Pooter J., Sander T., Schneider T.:
    Experimental determination of the dose rate constant for selected 125I- and 192Ir-brachytherapy sources.
    Metrologia 49, 2012, S219 - S222

Contact:
Dr. Thorsten Schneider
Phone: +49 (0) 531 592 6346

BetaDosim: Software for the interpolation of the dose rate due to the beta emission of radionuclides

The software "BetaDosim" interpolates the dose rate per activity of plane radioactive sources located on a steel plate, see figure. The output is the dose rate per activity due to the beta emission of a radionuclide with a given beta endpoint energy, Eß,max, a given source diameter, ddiam, and at a given distance from the source, rdist, with air between the source and the point of interest.

The software "BetaDosim" is freely available.

Literature

Contact