22 research outputs found
Semi-empirical formulation of multiple scattering for Gaussian beam model of heavy charged particles stopping in tissue-like matter
Dose calculation for radiotherapy with protons and heavier ions deals with a
large volume of path integrals involving a scattering power of body tissue.
This work provides a simple model for such demanding applications. There is an
approximate linearity between RMS end-point displacement and range of incident
particles in water, empirically found in measurements and detailed
calculations. This fact was translated into a simple linear formula, from which
the scattering power that is only inversely proportional to residual range was
derived. The simplicity enabled analytical formulation for ions stopping in
water, which was designed to be equivalent with the extended Highland model and
agreed with measurements within 2% or 0.02 cm in RMS displacement. The
simplicity will also improve the efficiency of numerical path integrals in the
presence of heterogeneity.Comment: 6 pages, 3 figures, submitted to Physics in Medicine and Biolog
Computational modeling of beam-customization devices for heavy-charged-particle radiotherapy
A model for beam customization with collimators and a range-compensating
filter based on the phase-space theory for beam transport is presented for dose
distribution calculation in treatment planning of radiotherapy with protons and
heavier ions. Independent handling of pencil beams in conventional pencil-beam
algorithms causes unphysical collimator-height dependence in the middle of
large fields, which is resolved by the framework comprised of generation,
transport, collimation, regeneration, range-compensation, and edge-sharpening
processes with a matrix of pencil beams. The model was verified to be
consistent with measurement and analytic estimation at a submillimeter level in
penumbra of individual collimators with a combinational-collimated carbon-ion
beam. The model computation is fast, accurate, and readily applicable to
pencil-beam algorithms in treatment planning with capability of combinational
collimation to make best use of the beam-customization devices.Comment: 16 pages, 5 figure
Theoretical methods for the calculation of Bragg curves and 3D distributions of proton beams
The well-known Bragg-Kleeman rule RCSDA = A dot E0p has become a pioneer work
in radiation physics of charged particles and is still a useful tool to
estimate the range RCSDA of approximately monoenergetic protons with initial
energy E0 in a homogeneous medium. The rule is based on the
continuous-slowing-down-approximation (CSDA). It results from a generalized
(nonrelativistic) Langevin equation and a modification of the phenomenological
friction term. The complete integration of this equation provides information
about the residual energy E(z) and dE(z)/dz at each position z (0 <= z <=
RCSDA). A relativistic extension of the generalized Langevin equation yields
the formula RCSDA = A dot (E0 +E02/2M dot c2)p. The initial energy of
therapeutic protons satisfies E0 << 2M dot c2 (M dot c2 = 938.276 MeV), which
enables us to consider the relativistic contributions as correction terms.
Besides this phenomenological starting-point, a complete integration of the
Bethe-Bloch equation (BBE) is developed, which also provides the determination
of RCSDA, E(z) and dE(z)/dz and uses only those parameters given by the BBE
itself (i.e., without further empirical parameters like modification of
friction). The results obtained in the context of the aforementioned methods
are compared with Monte-Carlo calculations (GEANT4); this Monte-Carlo code is
also used with regard to further topics such as lateral scatter, nuclear
interactions, and buildup effects. In the framework of the CSDA, the energy
transfer from protons to environmental atomic electrons does not account for
local fluctuations.Comment: 97 pages review pape