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Measurements aimed at investigating the quenching of sensitivity of Gafchromic EBT3 films irradiated with charged particles at radiotherapy energy levels have been carried out. Films have been irradiated with beams of protons and carbon ions of interest for Hadron Therapy. The broadening of pencil beams in water phantom as a function of initial energy has been studied and the quenching of EBT3 film sensitivity has been quantified. A procedure for correcting the dose images obtained by means of EBT3 films has been improved and its application to an irradiation test has show the validity of the proposed methodology.

The various dose components generated by epithermal neutron beams in tissue-equivalent materials have different spatial distributions that also depend on the size and volume of the irradiated volume. NCT dosimetry requires the separate determination of dose components having different LET, because of their different RBE. Monte Carlo simulations have been developed concerning the absorbed doses and thermal neutron fluences, to investigate the extent of the differences that may occur by changing the shape and size of the irradiated volumes. Moreover, the doses and fluences that occur if specific isotopes (10B, 14N, 157Gd) are added to water have been evaluated.

The quenching of sensitivity of gafchromic films EBT3 with increasing radiation LET is studied and a proposed method for correcting the measured dose images is described. The method evaluates a correction coefficient in each position of the acquired image by multiplying the measured dose value for a calculated ratio of the absorbed dose to the measured one. Such calculated doses are obtained utilising knowledge about absorbed and measured doses for single Bragg peaks from protons of a generic energy E. This topic is under study and the software in MATLAB developed for achieving the correction of the measured images is continuously implemented. The first results to test the validity of the proposed method also for complex dose distributions are promising.

Purpose Gafchromic films could be valid detectors for in-phantom dose controls in hadrontherapy but the quenching of their sensitivity with increasing the linear energy transfer (LET) of radiation brings a limit to their utilisation. This effect is manifest in the case of exposures to protons but it is really noticeable for carbon ions, whose LET is high also at the beam-entrance position. A method for correcting dose images acquired with films irradiated with proton beams has been initially proposed and tested with high approximations [1] and then developed with more exhaustive procedure [2] . In this work, studies aimed at applying the method, in his final structure, to carbon ions are carried out. Methods Gafchromic EBT3 films that were suitably placed in a solid-water phantom and exposed to carbon ion beams at the synchrotron of CNAO (Pavia, Italy). Optical analyses were performed with conventional scanner or laboratory-made instrument for light-transmittance detection. The method for amending dose images evaluates, in each image point, a correction coefficient obtained evaluating, for each pencil beam (PB) giving dose contribution in the considered position, both the absorbed dose and the measured one and, finally, their ratio. Dedicated software in MATLAB has been developed for attaining the corrected images. Results Correction algorithms require 3D knowledge of both absorbed and measured doses for each PB. Measurements and calculations have been performed with PBs of various energies and fitting parameters were deduced. Conclusions The proposed method for amending the experimental images has proved to be promising and, upon completion of the software, will be suitable for the use in clinical practice.

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 (RBE α ) 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.