Received 16 November 2007; received in revised form 4 July 2008; accepted 23 July 2008. published online 09 January 2009.
Purpose
The objective of this experiment was to compare the oncogenic potential of carbon ion beams and conventional photon beams for use in radiotherapy.
Methods and Materials
The HeLa X human skin fibroblast cell line CGL1 was irradiated with carbon ions of three different energies (270, 100, and 11.4 MeV/u). Inactivation and transformation data were compared with those for 15 MeV photons.
Results
Inactivation and transformation frequencies for the 270 MeV/u carbon ions were similar to those for 15-MeV photons. The maximal relative biologic effectiveness (RBEα) values for 100MeV/u and 11.4 MeV/u carbon ions, respectively, were as follows: inactivation, 1.6 ± 0.2 and 6.7 ± 0.7; and transformation per surviving cell, 2.5 ± 0.6 and 12 ± 3. The curve for dose-transformation per cell at risk exhibited a maximum that was shifted toward lower doses at lower energies.
Conclusions
Transformation induction per cell at risk for carbon ions in the entrance channel was comparable to that for photons, whereas for the lower energies, 100 MeV/u and 11 MeV/u, which are representative of the energies delivered to the tumor margins and volume, respectively, the probability of transformation in a single cell was greater than it was for photons. In addition, at isoeffective doses with respect to cell killing, the 11.4-MeV/u beam was more oncogenic than were photons.
Reprint requests to: Daniela Bettega, Ph.D., Dipartimento di Fisica, Via Celoria 16-20133 Milano, Italy. Tel: ++390250317210; Fax: ++390250317630
This research project was supported in part by the European Commission under the 6th Framework Programme through the Integrated Infrastructure Initiative on EUROpean Nuclear Structure (EURONS), Contract No. Rii3-CT-2004-506065, and by the Italian Space Agency (Contract MO-MA 1 B1341-X5 COUNT).
ABSTRACT