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In Search of the Optimum Ion for Radiotherapy

F Guan

F Guan1*, U Titt1, M Bangert2, R Mohan1, (1) UT MD Anderson Cancer Center, Houston, TX, (2) DKFZ, German Cancer Research Center, Heidelberg, Germany

SU-E-T-502 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To investigate the physical and biological properties and the clinical potential of several different ions through computer simulations.
Methods: Using the Geant4 Monte Carlo toolkit, we calculated spatial dose and LET distributions in a water phantom for monoenergetic beams for four candidate ions with the same range (28 cm in water): 207 MeV/u protons, 244 MeV/u ³He ions, 206 MeV/u ⁴He ions, and 400 MeV/u ¹²C ions. An ideal broad beam of 6 cm in diameter was used in the simulations. The scoring voxel volume was set to 1 cubic millimeter. We also recorded the dose contributions from several major nuclear fragments. Furthermore, data for a 5-cm RBE-weighted dose SOBP for ¹²C ions with a range of 30 cm were analyzed.
Results: Simulation results showed advantages and disadvantages of each ion. For instance, a ¹²C ion beam produces the sharpest and narrowest Bragg peak, and the smallest penumbra, but it has the highest entrance to peak dose ratio, and highest and longest nuclear fragmentation tail. Furthermore, the lateral dose halo effect of ¹²C is substantially greater than other ions. For the same range in water, ³He and ⁴He ions show very similar features. They have smaller lateral penumbrae than protons, and much smaller fragmentation tails compared with ¹²C ions. Although protons have the largest lateral penumbra and widest Bragg peak, they do not have an observable fragmentation tail. For a pristine beam of 400 MeV/u ¹²C ions, the fragmentation tail dose is 15% of the peak dose. In the case of 5-cm SOBP with 30-cm range of ¹²C ions, the fragmentation tail dose can be as high as 30% of the maximum dose.
Conclusion: Each type of ion has special advantages and disadvantages. Further research is needed to consider additional factors such as energy dependence, cost effectiveness and RBE.

Funding Support, Disclosures, and Conflict of Interest: NCI grant P01CA021239

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