Room: Karl Dean Ballroom A2
Purpose: Relative biological effectiveness (RBE) is an important quantity in planning particle therapy. However, it is not a quantity that easily lends itself to measurements or computation as it depends on many biological and physical quantities. The physical quantity called linear energy transfer (LET) has been demonstrated to be a good surrogate for RBE and has been proposed to be included in routine particle therapy treatment planning. In order to properly incorporate LET in clinical treatment, it is important to be able to experimentally measure and verify LET distribution.
Methods: We propose to measure LET using a dual chamber system consisting of an air ionization chamber and a liquid ionization chamber by exploiting the difference in observed recombination due to LET between the two ionization chambers. The resulting difference in the measured signals is used to directly extract the LET of an actual treatment beam in real time.
Results: Experiments were performed to verify the proposed method. The dual chamber assembly consisted of an air-filled ionization chamber (PTW Roos Type 34073) and a liquid-filled ionization chamber (PTW MicroLion). The system was irradiated under proton, carbon and oxygen ion beams at two different energies at different depths along the beam direction. The ratio between the two chamber readings were then curve fitted to the LET values obtained through Monte Carlo simulations to produce the calibration curves for each ion species and each energy. Analysis of these calibration curves indicated that they are in fact independent of ion species and energies, and can be used to produce LET measurements within an error band of Â± 10%.
Conclusion: A dual chamber method for measuring LET has been developed. Experiments indicate it can produce accurate LET measurements and has particle species and energy independence.
Funding Support, Disclosures, and Conflict of Interest: NIH NCI 1R21CA197325
LET, Liquid Ionization Chamber, Monte Carlo
TH- External Beam- Particle therapy: Carbon ion therapy - Development (new technology and techniques)