IJMPCERO  Vol.6 No.2 , May 2017
LET Monitoring Using Liquid Ionization Chambers
Abstract: Relative biological effectiveness (RBE) is an important quantity in planning particle beam cancer therapy. In general, the RBE describes the biological effectiveness of a given primary beam with respect to a reference photon irradiation. RBE varies not only for different primary beams but also with depth in the target for a given beam modality. It is not a quantity that easily lends itself to measurements or computation as it depends on many biological and physical quantities. Numerous experiments in vitro using various cell lines and irradiation modalities have shown that a general relationship between RBE and the physical quantity Linear Energy Transfer (LET) exists. Several groups have proposed including LET in the radiation therapy treatment planning instead of the more complicated and elusive RBE. It has been shown that LET is an important quantity to consider in treating radio-resistant tumors. The concept of LET painting has been proposed with the goal of improving tumor control probability (TCP) for hypoxic tumors by focusing high LET radiation on the hypoxic region of the tumor while restricting the surrounding normal tissue to low LET radiation. In order to properly incorporate LET in clinical treatment, it is important to be able to experimentally measure and verify LET distribution. We propose a novel method for measuring LET using a dual chamber methodology exploiting the difference in the observed recombination between air filled ionization chambers (IC) and liquid filled ionization chambers (LIC). The resulting difference in the measured signals will be used to directly extract the relative LET of an actual treatment beam in real time. This paper describes our initial studies of this method, presents preliminary results, and discusses further improvements toward a practical real-time LET measuring device.
Cite this paper: Tegami, S. , Bello, S. , Luan, S. , Mairani, A. , Parodi, K. and Holzscheiter, M. (2017) LET Monitoring Using Liquid Ionization Chambers. International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 6, 197-207. doi: 10.4236/ijmpcero.2017.62018.

[1]   Wouters, B.G., Lam, G.K.Y., Oelfke, U., Gardey, K., Durand, R.E. and Skarsgard, L.D. (1996) Measurements of Relative Biological Effectiveness of the 70 MeV Proton Beam at TRIUMF Using Chinese Hamster V79 Cells and the High-Precision Cell Sorter Assay. Radiation Research, 146, 159-170.

[2]   Paganetti, H. (2014) Relative Biological Effectiveness (RBE) Values for Proton Beam Therapy. Variations as a Function of Biological Endpoint, Dose, and Linear Energy Transfer. Physics in Medicine and Biology, 59, R419-R472.

[3]   Lomax, T. (2016) Invited Talk at ICTR-PHE 2016, Geneva, Switzerland.

[4]   Singers Sørensen, B., Overgaard, J. and Bassler, N. (2011) In Vitro RBE-LET Dependence for Multiple Particle Types. Acta Oncologica, 50, 757-762.

[5]   Bassler, N., Jäkel, O., Søndergaard, S.S. and Petersen, J.B. (2010) Dose- and LET-Painting with Particle Therapy. Acta Oncologica, 49, 1170-1176.

[6]   Bassler, N., et al. (2014) LET-Painting Increases Tumour Control Probability in Hypoxic Tumours. Acta Oncologica, 53, 25-32.

[7]   Wickman, G. (1974) A Liquid Ionization Chamber with High Spatial Resolution. Physics in Medicine and Biology, 19, 66-72.

[8]   Bahar-Gogani, J., Grindborg, J.E., Johansson, B.E. and Wickman, G. (2001) Long-Term Stability of Liquid Ionization Chambers with Regard to Their Qualification as Local Reference Dosimeters for Low Dose-Rate Absorbed Dose Measurements in Water. Physics in Medicine and Biology, 46, 729-740.

[9]   Dasu, A., Löfroth, P. and Wickman, G. (1998) Liquid Ionization Chamber Measurements of Dose Distributions in Small 6 MV Photon Beams. Physics in Medicine and Biology, 43, 21-36.

[10]   Onsager, L. (1938) Initial Recombination of Ions. Physical Review, 54, 554-557.

[11]   Jaffé, G. (1940) On the Theory of Recombination. Physical Review, 58, 968-976.

[12]   Johansson, B. and Wickman, G. (1997) General Collection Efficiency for Liquid Isooctane and Tetramethylsilane Used as Sensitive Media in a Parallel-Plate Ionization Chamber. Physics in Medicine and Biology, 42, 133-145.

[13]   Tegami, S. (2012) Liquid Ionization Chambers for Quality Assurance of High-Let Beams. International Conference on Translational Research—Physics for Health, ICTR-PHE 2012, Geneva.

[14]   Tegami, S. (2013) LET Measurements with a Liquid Ionization Chamber. Ph.D. Thesis, University of Heidelberg, Heidelberg.

[15]   Eberle, K., et al. (2003) First Tests of a Liquid Ionization Chamber to Monitor Intensity Modulated Radiation Beams. Physics in Medicine and Biology, 48, 3555-3564.

[16]   Pardo, J., et al. (2005) Development and Operation of a Pixel Segmented Liquid-Filled Linear Array for Radiotherapy Quality Assurance. Physics in Medicine and Biology, 50, 1703-1716.

[17]   Ferrari, A., Sala, P.R., Fasso, A. and Ranft, J. (2005) FLUKA: A Multi-Particle Transport Code. CERN-2005-10 INFN/TC_05/11, SLAC-R-773.

[18]   Böhlen, T., et al. (2014) The FLUKA Code: Developments and Challenges for High Energy and Medical Applications. Nuclear Data Sheets, 120, 211-214.

[19]   Mairani, A., Brons, S., Cerutti, F., Fassó, A., Ferrari, A., Krämer, M., Parodi, K., Scholz, M. and Sommerer, F. (2010) The FLUKA Monte Carlo Code Coupled with the Local Effect Model for Biological Calculations in Carbon Ion Therapy. Physics in Medicine and Biology, 55, 4273-4289.

[20]   Böhlen, T.T., Cerutti, F., Dosanjh, M., Ferrari, A., Gudowska, I., Mairani, A. and Quesada, J.M. (2010) Benchmarking Nuclear Models of FLUKA and GEANT4 for Carbon Ion Therapy. Physics in Medicine and Biology, 55, 5833-5847.

[21]   Ferrari, A., et al. (1992) An Improved Multiple Scattering Model for Charged Particle Transport. Nuclear Instruments and Methods, B71, 412-426.

[22]   Parodi, K., Mairani, A., Brons, S., Hasch, B.G., Sommerer, F., Naumann, J., Jäkel, O., Haberer, T. and Debus, J. (2012) Monte Carlo Simulations to Support Start-Up and Treatment Planning of Scanned Proton and Carbon Ion Therapy at a Synchrotron-Based Facility. Physics in Medicine and Biology, 57, 3759-3784.

[23]   Parodi, K., Mairani, A. and Sommerer, F. (2013) Monte Carlo-Based Parametrization of the Lateral Dose Spread for Clinical Treatment Planning of Scanned Proton and Carbon Ion Beams. Journal of Radiation Research, 54, 191-196.

[24]   Wang, L.L.W., Perles, L.A., Archambault, L., Sahoo, N., Mirkovic, D. and Beddar, S. (2012) Determination of the Quenching Correction Factors for Plastic Scintillation Detectors in Therapeutic High-Energy Proton Beams. Physics in Medicine and Biology, 57, 7767-7781.