Program Information
Parametrization of Nanodosimetric Quantities for Fast Calculation in Clinical Proton and Light Ion Therapy Beams
J Ramos-Mendez1*, L Burigo2 , R Schulte3 , B Faddegon1 , (1) University of California San Francisco, San Francisco, CA, (2) German Cancer Research Center DKFZ, Heidelberg, Heidelberg, (3) Loma Linda University, Loma Linda, CA
Presentations
SU-K-205-12 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 205
Purpose: To provide a parametrized database of the most commonly used nanodosimetric quantities in proton and light-ion therapy for fast calculation of the distribution of these quantities in phantoms and patients.
Methods: TOPAS-nBio was used to pre-calculate the ionization cluster size distributions of light ions from proton to oxygen with kinetic energy between 1-1000 MeV/u using detailed-history Monte Carlo simulations in liquid water. Ionization clustering was scored inside cylinders of the size of 10 base pairs (3.4 nm in length, 2.3 nm in diameter) randomly located and oriented in an enclosing chromatin-size volume. Nanodosimetric quantities (e.g., the conditional mean m₁(Q) and conditional cumulative probability f₃(Q) of the ionization cluster size distribution) were parametrized for each ion as a function of incoming energy. Fast calculations in a patient geometry were performed in millimeter-sized voxels with a specialized scorer using the parametrized data. Accuracy was verified by calculating dose-weighted m₁(Q) and f₃(Q) distributions in a 20x20x20 cm³ water phantom irradiated with monoenergetic 390 MeV/u carbon ions. Results were compared to full track structure simulations of the irradiation of nanometer-sized regions positioned along several depths in the carbon Bragg curve.
Results: The parametrized database had on average 0.3% standard deviation for all ions and all energies. The specialized scorer using the parametrized data ran as fast as regular dose distributions calculations. In addition, it agreed within 1% and 3% for the m₁(Q) and f₃(Q), respectively, with the full track structure simulation results in the region upstream and including the carbon Bragg peak. For those regions at the tail of the Bragg peak, significant differences outside the statistical tolerances, attributed to the lack of light-ions in the track-structure simulation, are under further investigation.
Conclusion: The parametrized database provides fast calculation of spatial distributions of nanodosimetric quantities in condensed-history simulations of proton and light-ion radiotherapy.
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