Article

Calculation of energy-deposition distributions and microdosimetric estimation of the biological effect of a 9C beam.

Nuclear Engineering, Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
Biophysik (Impact Factor: 1.75). 01/2009; 48(2):135-43. DOI: 10.1007/s00411-008-0206-8
Source: PubMed

ABSTRACT Among the alternative beams being recently considered for external cancer radiotherapy, (9)C has received some attention because it is expected that its biological effectiveness could be boosted by the beta-delayed emission of two alpha particles and a proton that takes place at the ion-stopping site. Experiments have been performed to characterise this exotic beam physically and models have been developed to estimate quantitatively its biological effect. Here, the particle and heavy-ion transport code system ( PHITS ) is used to calculate energy-deposition and linear energy transfer distributions for a (9)C beam in water and the results are compared with published data. Although PHITS fails to reproduce some of the features of the distributions, it suggests that the decay of (9)C contributes negligibly to the energy-deposition distributions, thus contradicting the previous interpretation of the measured data. We have also performed a microdosimetric calculation to estimate the biological effect of the decay, which was found to be negligible; previous microdosimetric Monte-Carlo calculations were found to be incorrect. An analytical argument, of geometrical nature, confirms this conclusion and gives a theoretical upper bound on the additional biological effectiveness of the decay. However, no explanation can be offered at present for the observed difference in the biological effectiveness between (9)C and (12)C; the reproducibility of this surprising result will be verified in coming experiments.

0 Bookmarks
 · 
95 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate the potential importance of radioactive 9C-ion beam in cancer radiotherapy. Human salivary gland (HSG) cells were exposed to a double-radiation-source 9C beam at different depths around the Bragg peak. Cell survival fraction was determined by standard clonogenic assay. For comparison, the same experiment was conducted for a therapeutic 12C beam. To determine relative biologic effectiveness (RBE) values, HSG cells were also irradiated with 60Co gamma-rays of fractionation scheme as the reference. The 9C beam was more efficient in cell killing at the depths around its Bragg peak than was the 12C beam, which corresponded to the 9C-ion stopping region and where delayed low-energy particles were emitted. The RBE value at 50% survival level for the 9C beam varied from 1.38 to 4.23. Compared with the 12C beam, the RBE values for the 9C beam were always higher; an increase in RBE by a factor of up to 1.87 has been observed at the depths distal to the Bragg peak. The potential advantage of radioactive 9C-ion beam in cancer therapy has been revealed at low dose rate in comparison with a therapeutic 12C beam. This observation, however, remains to be investigated at therapeutic dose rates in the future.
    International Journal of Radiation OncologyBiologyPhysics 12/2005; 63(4):1237-44. · 4.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A method of calculating cell survival from microdosimetric spectra for high-LET radiations and exponential cell survival is discussed. The basis of the calculation is that a cell nucleus receiving a specific dose D has a probability of survival of exp(-D/Do), where Do, the specific lethal dose, is assumed to be independent of cell size and shape. A relationship between specific lethal dose and mean lethal dose is derived. This approach gives the result that mean lethal dose is sensitive to both cell size and shape (cells with disc-shaped and spherical nuclei are treated) and therefore its uses as an indicator of cell sensitivity at high LET must be viewed with caution.
    International Journal of Radiation Biology 03/1991; 59(2):447-57. · 1.84 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Due to their favourable properties such as high dose localization and high RBE heavy-ion beams have attracted increasing interest in cancer treatment. Efforts to exploit these advantages to the maximum extent in cancer therapy have never been given up. A new idea of applying a radioactive ion beam with beta-delayed particle decay such as 9C or 8B to cancer therapy is put forward in this paper. A model to evaluate the biological effect in terms of cell survival induced by the emitted particles from the decays of the stopped ions has been established. Because of the difference of the internally emitted particle irradiation from the external ion beam, the microdosimetric quantity such as specific energy is applied to evaluate the cell surviving effect induced by the emitted particles from the decays of the radioactive ions. Within the framework of this model, the cell-killing effects resulting from the emitted particles were calculated under different conditions. Finally, the potential application of the radioactive ion beam 9C in cancer therapy is demonstrated.
    Physics in Medicine and Biology 10/2003; 48(18):2971-86. · 2.70 Impact Factor