Dosimetric evaluation of nuclear interaction models in the Geant4 Monte Carlo simulation toolkit for carbon-ion radiotherapy.

We tested the ability of two separate nuclear reaction models, the binary cascade and JQMD (Jaeri version of Quantum Molecular Dynamics), to predict the dose distribution in carbon-ion radiotherapy. This was done by use of a realistic simulation of the experimental irradiation of a water target. Comparison with measurement shows that the binary cascade model does a good job reproducing the spread-out Bragg peak in depth-dose distributions in water irradiated with a 290 MeV/u (per nucleon) beam. However, it significantly overestimates the peak dose for a 400 MeV/u beam. JQMD underestimates the overall dose because of a tendency to break a nucleus into lower-Z fragments than does the binary cascade model. As far as shape of the dose distribution is concerned, JQMD shows fairly good agreement with measurement for both beam energies of 290 and 400 MeV/u, which favors JQMD over the binary cascade model for the calculation of the relative dose distribution in treatment planning.

Isolation and characterization of defective-interfering particles of poliovirus Sabin 1 strain.

Defective-interfering (DI) particles of the Sabin strain of type 1 poliovirus were generated on serial high m.o.i. passaging. The deletions, measured by agarose gel electrophoresis, appeared to comprise approximately 10% of the total genome. Analysis of the RNAs, after digestion with RNase T1, by two-dimensional polyacrylamide gel electrophoresis revealed that the locations of the deleted genome regions were similar to those of the DI particles of the Mahoney strain of type 1 poliovirus (A. Nomoto, A. Jacobson, Y. F. Lee, J. Dunn, and E. Wimmer, (1979), J. Mol. Biol. 128, 179-196). Taking the known nucleotide sequences of the total genome and large RNase T1-resistant oligonucleotides into account, the deletions of almost all DI RNAs were found to exist between nucleotide positions 1307 and 2630, a genome region encoding capsid polypeptides VP2, VP3, and VP1. In cells coinfected with the purified DI particles and the Sabin strain of type 2 or type 3 poliovirus, particles containing the DI genomes were effectively produced. These results suggest that encapsidation signals are conserved in all three serotypes of polioviruses. However, only a very small amount of similar DI particles appeared to be produced in cells coinfected with coxsackie virus B1, although the genomes of polioviruses and coxsackie viruses have common sequences and therefore these viruses are considered to have arisen from a common ancestor. These data may suggest differences in encapsidation signals between polioviruses and coxsackie viruses.