Boscolo, D.

Durante, M.

Krämer, M.

Rosso, V.

Scifoni, E.

GSI Repository

TLD Efficiency calculation for heavy ions: a new approach∗D. Boscolo1,2, E. Scifoni1, M. Durante1, V. Rosso4, and M. Kra¨mer11GSI, Darmstadt, Germany; 2University of Pisa, ItalyThermoluminescence dosimeters (TLDs) are solid statedetectors widely used in conventional radiation detectionand dose verification. The development of ion beam cancertherapy and the research in radioprotection in space stim-ulated the use of the TLDs for heavy ions dosimetry. Themain advantages of this kind of detector, compared, e.g.,to ionization chambers, are the small dimensions, ease ofhandling, no interference on the radiation field and the us-ability in solid state phantoms. However the response ofTLDs with dose is non-linear. It can be supralinear andsaturation effects appear as well. The response of these de-tectors when irradiated with particle beams depends alsostrongly on the quality of the radiation. For this reason,in order to use TLDs with particle beams, and specifically,to get a prediction of their response in a treatment plan, amodel that can reproduce the behavior of these detectors indifferent conditions is needed.A new, simple and completely analytical, algorithm forthe calculation of the efficiency depending on ion charge Zand energy E has been developed.The approach investigated is based on the amorphous trackstructure model and on the knowledge of radial dose dis-tribution for heavy ions D(r) and of the detector responseto reference radiation, for this work X-ray, TLγ. The re-sponse of the whole detector has been evaluated startingfrom the response to a single ion of the beam and consider-ing the contributions of dose from the neighbouring tracksas adding up in a linear regime. This approach is realisticin a low dose approximation.The relative efficiency R.E. has been derived accordingtoR.E =SHISγ∣∣∣∣D(1)using SHI and Sγ the integral light sum of detector irra-diated with heavy ions and X-ray, respectively.Since X-ray’s response curve is known and the dose de-position is uniform, the signal can be calculated directlyfrom the total dose delivered by the ion. The thermolumi-nescence caused by ion is derived asSHI = 2π∫ rmax0TLγ(D(r))rdr (2)where rmax is the maximum range of the secondary elec-trons.In figure 1 it is shown the agreement of the present modelwith experimental data. Its main advantage, is that being∗Work supported by University of Pisa’s Erasmus Placements project 0.01 0.1 1 1  10  100R.EE (MeV/u)ProtonCalculationExperiment 0.01 0.1 1 1  10  100R.EE (MeV/u)CarbonCalculationExperimentFigure 1: A comparison between experimental relative ef-ficiency data [1] and calculation with the present approachfor protons (up) and carbon ions (down).fully analytical is computationally fast and can be then ef-ficiently integrated in treatment planning verification tools.Furthermore, it is robust against modifications of the radialdose distribution of a single ion in the detector, as well asto different detector response models. A comparison with astatistical method based on Kellerer algorithm [2] has beenalso done, returning a good agreement.References[1] O. B. Geiß , M. Kra¨mer, and G. Kraft. Efficiency of thermo-luminescence detectors to heavy charged particles. NIM B,142:592–598, 1998.[2] S. Greilich et al., Efficient calculation of local dose distribu-tion for response modelling in proton and ion beams (submit-ted), arXiv:1306.0185v1.GSI SCIENTIFIC REPORT 2013 BIOPHYSICS-39doi:10.15120/GR-2014-1-BIOPHYSICS-39 241

TLD Efficiency calculation for heavy ions: a new approach

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TLD Efficiency calculation for heavy ions: a new approach

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