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A Mechanism-Based Approach to Predict the
Relative Biological Effectiveness of Protons and Carbon Ions in Radiation
Therapy
M.C. Frese, V.K. Yu,
R. D. Stewart,
D.J. Carlson
Int. J. Radiat. Biol. Phys. 83,
442-450 (2012)
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Purpose: The physical and
potential biological advantages of proton and carbon ions have not
been fully exploited in radiation therapy for
the treatment of cancer. In this work, an approach to
predict proton and carbon ion relative
biological effectiveness (RBE) in a representative spreadout
Bragg peak (SOBP) is derived using the
repair-misrepair-fixation (RMF) model.
Methods and
Materials: Formulas linking dose-averaged linear-quadratic
parameters to DSB
induction and processing are derived from the
RMF model. The Monte Carlo Damage Simulation
(MCDS)
software is used to quantify the effects of radiation quality on the
induction of
DNA
double-strand breaks (DSB). Trends in parameters
a and b
for clinically relevant proton
and carbon ion kinetic energies are
determined.
Results: Proton and carbon
ion RBE are shown to increase as particle energy, dose, and tissue
a/b ratios
decrease. Entrance RBE is ~ 1.0 and ~ 1.3 for protons and carbon ions,
respectively.
For doses in the range of 0.5 to 10 Gy, proton RBE ranges from 1.02
(proximal edge) to 1.4
(distal edge). Over the same dose range, the
RBE for carbon ions ranges from 1.5 on the proximal
edge to 6.7 on the distal edge.
Conclusions:
The proposed approach is advantageous because the RBE for clinically
relevant
particle distributions is guided by well-established physical and
biological (track structure)
considerations. The use of an independently
tested Monte Carlo model to predict the effects
of radiation quality on DSB induction also
minimizes the number of ad hoc biological parameters
that must be determined to predict RBE. Large
variations in predicted RBE across an
SOBP may produce undesirable biological hot
and cold spots. These results highlight the potential
for the optimization of physical dose for a
uniform biological effect..
Keywords:
Carbon ions, Cell survival, Protons, RBE, Repair-misrepair-fixation
(RMF) model |