The logical progression in the technology of particle therapy may be the eventual adoption of clinical carbon ion beams. With the increasing popularity of clinical heavy particle radiotherapy, proton LET simulations are of increasing relevancy. In view of the beam path of the carbon beam is littered with a variety of secondary particles possessing a wide range of LET values, more reliable model parameters and clinical trials are needed for exploration of the advantage of carbon ion radiation therapy. concluded the optimum hadronic therapy to be that with lithium pencil beams (followed by beryllium and boron), possessing a localized high-LET (>20 keV/µm) component at the end of its range while maintaining low (<10 keV/µm) LET values in normal tissues. Studying a number of potential light-ion beams, Kempe et al. Due to a greater distribution of dose beyond the Bragg peak, carbon beams are not generally considered to be dosimetrically superior to protons the correlations between LET, RBE, and an ion's charge and mass are not as yet well-established.īrahme determined values, based on biological parameters, that place an optimum LET for cell killing at 25–75 keV/µm, while urging minimization of the LET to normal tissues. With the comparable dose conformity of protons and carbon ions, they differ most in their RBE, because of their different LET. Where ϕ E is the particle fluence in energy E, at the depth d, and S (E) is the stopping power of a specific particle type of energy E.Īccelerators may produce a variety of ion beams, of which proton and carbon ion beams are the most common in clinical use. The dose-averaged LET used in this study is defined as The contributions of nuclear interactions are crucial for light-ion beam therapy, as the production of secondary particles having significant LET values can cause a potential increase in the RBE of the beam.įor a secondary particle with specific charge and velocity, the term LET is determined by the energy transferred from a large number of particles of the same type to a localized region, on average, per unit path length. LET definitions are based on the stopping power values used to describe the gradual loss of energy of the incoming ion per unit path length as it penetrates an absorbing material it is the sum of the electronic and nuclear collision stopping power and the radioactive stopping power. It is generally accepted that the RBE is dependent upon the dose, dose fractionation, tissue type, biological endpoint, and the local particle energy spectrum, which is usually referred as radiation quality and can be characterized by the LET. Increased linear energy transfer (LET) along the beam path implies a greater ionization density, and thus an enhanced RBE. Coupled with a greater relative biological effectiveness (RBE), the potentially higher therapeutic ratio implies an increase in the tumor control probability, and a reduction of the normal tissue complication probability.ĭose conformity in ion beam therapy is enhanced through the properties of the Bragg peak. Carbon ion therapy may be one of the most promising forms of light-ion therapy, and studies regarding the production of secondary particles from the interaction of carbon ions in water-like absorber materials, and subsequently the interactions of secondary particles in the same materials, predict the importance of this therapy for clinical use. Ion beam radiotherapy has the potential to achieve dose conformity indices higher than those of traditional photon therapy. The results of the simulations show that the secondary particles that contributed a major dose component had LETs 600 keV/µm contributed only <0.3% of the dose. The dose-averaged LET and the dose contributions of primary and secondary particles were calculated from the simulation. A 1 mm diameter carbon ion pencil beam with energies per nucleon of 155, 262, and 369 MeV was used in a geometry and tracking 4 Monte Carlo simulation to interact in a 27 L water phantom containing 3000 rectangular detector voxels.
Our primary objective in this study was to classify and quantify the secondary particles produced, their dose averaged LETs, and their dose contributions in the absorbing material. The secondary particles may have linear energy transfer (LET) values that potentially increase the relative biological effectiveness of the beam. The factors influencing carbon ion therapy can be predicted from accurate knowledge about the production of secondary particles from the interaction of carbon ions in water/tissue-like materials, and subsequently the interaction of the secondary particles in the same materials.
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