Berlin 2005 – scientific programme

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ST: Strahlen- und Medizinphysik

ST 8: Strahlenphysik: Strahlenbiophysik II

ST 8.3: Fachvortrag

Wednesday, March 9, 2005, 14:30–14:45, TU HL1

Proton RBE at low energies — •Mareike Mueller — GSI, Darmstadt

In proton therapy, an average RBE of 1 to 1.2 is used for the calculation of treatment plans although the RBE changes along the penetration depth. To verify this, CHO-K1 cells were irradiated in track segment experiments and experiments in which protons with a primary energy of 20 MeV were slowed down by thin degrader foils (polyethylene). The corresponding energy spectra were measured using a silicon detector. These show that in track segment irradiations, the energy spread is negligible. The energy spectra of the passively degraded protons are rather broad due to the energy straggling produced by the degrader foils which needs to be taken into consideration when calculating treatment plans. The RBE values of the track segment irradiations show a fairly sharp maximum at 2.50MeV. In the passive energy degrading experiments, the RBE values of the Bragg peak region do not show a sharp maximum, but are spread around a value lower than that of the track segment peak. It is expected that at higher energies as they are used in therapy, the RBE values will decrease even further in the Bragg peak region due to the larger energy straggling, but from the up to now conducted experiments, an RBE significantly greater than 1 can be expected.