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Strahlentherapie und Onkologie

, Volume 190, Issue 5, pp 459–466 | Cite as

Secondary radiation dose during high-energy total body irradiation

  • M. JaniszewskaEmail author
  • K. Polaczek-Grelik
  • M. Raczkowski
  • B. Szafron
  • A. Konefał
  • W. Zipper
Original article

Abstract

Aim

The goal of this work was to assess the additional dose from secondary neutrons and γ-rays generated during total body irradiation (TBI) using a medical linac X-ray beam.

Background

Nuclear reactions that occur in the accelerator construction during emission of high-energy beams in teleradiotherapy are the source of secondary radiation. Induced activity is dependent on the half-lives of the generated radionuclides, whereas neutron flux accompanies the treatment process only.

Materials and methods

The TBI procedure using a 18 MV beam (Clinac 2100) was considered. Lateral and anterior–posterior/posterior–anterior fractions were investigated during delivery of 2 Gy of therapeutic dose. Neutron and photon flux densities were measured using neutron activation analysis (NAA) and semiconductor spectrometry. The secondary dose was estimated applying the fluence-to-dose conversion coefficients.

Results

The main contribution to the secondary dose is associated with fast neutrons. The main sources of γ-radiation are the following: 56Mn in the stainless steel and 187W of the collimation system as well as positron emitters, activated via (n,γ) and (γ,n) processes, respectively. In addition to 12 Gy of therapeutic dose, the patient could receive 57.43 mSv in the studied conditions, including 4.63 μSv from activated radionuclides.

Conclusion

Neutron dose is mainly influenced by the time of beam emission. However, it is moderated by long source–surface distances (SSD) and application of plexiglass plates covering the patient body during treatment. Secondary radiation gives the whole body a dose, which should be taken into consideration especially when one fraction of irradiation does not cover the whole body at once.

Keywords

High-energy teleradiotherapy Whole-body irradiation Secondary radiation Induced radioactivity Neutron dose 

Sekundäre Strahlendosis während Ganzkörperbestrahlung am Linearbeschleuniger

Zusammenfassung

Ziel

Die zusätzliche Dosis durch sekundäre Neutronen- und γ-Strahlung während der Ganzkörperbestrahlung mit Röntgenstrahlung aus medizinischen Linearbeschleunigern wurde abgeschätzt.

Hintergrund

Bei der Emission hochenergetischer Strahlen zur Teletherapie finden hauptsächlich im Beschleuniger Kernreaktionen statt, die Sekundärstrahlung erzeugen. Die sich daraus ergebende Aktivität hängt von der Halbwertzeit der erzeugten Radionuklide ab, sekundäre Neutronenstrahlung tritt dagegen nur während des Behandlungsprozesses auf.

Materialien und Methoden

Bei Ganzkörperbestrahlung mit einem 18-MeV-Strahl (Clinac 2100) wurde der laterale und der anterior-posteriore bzw. posterior-anteriore Anteil während der Abgabe einer therapeutischen Dosis von 2 Gy pro Strahlenbehandlung untersucht. Neutronen- und Photonenflussdichten wurde mit Neutronenaktivierungsanalyse und Halbleiterspektrometrie bestimmt. Die Sekundärdosis wurde mithilfe von Fluss-Dosis-Umrechnungsfaktoren geschätzt.

Ergebnis

Der größte Anteil der Sekundärdosis hängt vom Fluss schneller Neutronen ab. Die Hauptquelle der γ-Strahlung sind 56Mn im Edelstahl und 187W des Fokussierungssystems sowie Positronenemitter, die über (n,γ)- bzw. (γ,n)-Prozesse aktiviert wurden. Zusätzlich zur therapeutischen Gesamtdosis von 12 Gy wird der Patient einer Dosis von bis zu 57,43 mSv ausgesetzt, davon 4,36 mSv aus aktivierten Radionukliden.

Schlussfolgerung

Die Neutronendosis hängt hauptsächlich von der Anzahl der abgegebenen Monitoreinheiten ab. Allerdings wird sie durch den großen Abstand zwischen Quelle und Oberfläche sowie die Verwendung von Plexiglasplatten zur Abdeckung des Patienten moderiert. Die Sekundärstrahlung setzt den ganzen Körper einer Dosis aus. Dies muss v. a. dann berücksichtigt werden, wenn eine Strahlenbehandlung nicht den ganzen Körper auf einmal betrifft.

Schlüsselwörter

Hochenergiefernbestrahlung Ganzkörperbestrahlung Sekundärstrahlung Induzierte Radioaktivität Neutronendosis 

Notes

Acknowledgments

Participation of BS in this research is supported by the “DoktoRIS scholarship program in favor of innovative Silesia” cofinanced by the European Union within the European Social Fund.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • M. Janiszewska
    • 1
    Email author
  • K. Polaczek-Grelik
    • 2
  • M. Raczkowski
    • 1
  • B. Szafron
    • 3
  • A. Konefał
    • 3
  • W. Zipper
    • 3
  1. 1.Medical Physics DepartmentLower Silesian Oncology CenterWroclawPoland
  2. 2.Medical Physics DepartmentUniversity of SilesiaKatowicePoland
  3. 3.Department of Nuclear Physics and Its ApplicationsUniversity of SilesiaKatowicePoland

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