Dresden 2011 – scientific programme

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ST: Fachverband Strahlen- und Medizinphysik

ST 1: Radiation Therapy I Fast Ions: Production, Physical Dosimetry, Biological Effets, Medical Effects

ST 1.5: Talk

Monday, March 14, 2011, 15:00–15:15, POT 112

New measurements of W-values in argon, nitrogen and air for protons, helium and carbon ions — •Jeannine Beck¹, Ulrich Giesen¹, Dieter Schardt², Markus Bender², and Daniel Severin² — ¹Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig — ²Helmholtzzentrum für Schwerionenforschung GmbH (GSI), Planckstraße 1, 64291 Darmstadt

In particle therapy for cancer the dosimetry of the charged-particle radiation is mostly performed by measuring the ionization produced in gas-filled ionization chambers. The conversion of the reading of an ionization chamber into absorbed dose requires W-values, which are defined as the average energy needed to produce an ion pair.

Because of the increasing importance of ion therapy and the lack of experimental W-values for heavy charged particles in air new measurements of W-values are being carried out at PTB and GSI. Existing measurements for protons in air indicate an uncertainty of 4 % and the main goal of the present studies is to achieve an accuracy of about 1 %. Preliminary results of measurements for protons, helium and carbon ions in argon, nitrogen and air in the energy region of 1 MeV/u up to 6 MeV/u will be discussed.