München 2004 – wissenschaftliches Programm

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ST: Strahlenphysik und Strahlenwirkung

ST 6: Strahlenwirkungen - Strahlentherapie II

ST 6.2: Fachvortrag

Donnerstag, 25. März 2004, 12:45–13:00, HS 129

Monte Carlo simulations for heavy ion dosimetry — •Oksana Filipenko¹, O Jäkel¹, P Andreo², N Sobolevsky³, and G Hartmann¹ — ¹DKFZ Heidelberg — ²IAEA, Vienna — ³Academy of Science, Moscow

In order to assure the accurate application of prescribed doses in carbon ion radiotherapy, appropriate dosimetric methods are needed. In clinical dosimetry it is common practice to use ionization chambers, calibrated in absorbed dose to water in Co60 field. The dose in the carbon ion beam is then obtained by the use of the beam quality correction factor, as suggested by the recent International Code of Practice for dosimetry TRS-398 of IAEA. This method is subjected to some uncertainties, connected to the fact that an ion beam in matter produces a spectrum of fragments due to the nuclear interactions. The major uncertainty (about 2 by the ratio of the stopping power values of ions in water relative to air. At present in TRS-398, a constant value of 1.13 is adopted for the stopping power ratio of ions. In order to investigate this value in detail, Monte Carlo simulations ( SHIELD-HIT, developed by N.Sobolevsky and P.Andreo) are used to calculate the complete spectrum of nuclear fragments resulting from the primary ion beam in different depths. Using these spectra and energy loss tables, the fluence weighted stopping power ratio can be determined more accurately. In the future mentioned code SHIELD-HIT will be used for further investigations in dosimetry.