Heavy-ions beams offer several advantages compared to other radiation such as low lateral scattering andhigh biological effectiveness (RBE) in the Bragg peak region, making them particularly attractive for thetreatment of radio-resistant tumours localized close to organs at risk . The extension of ion therapy tonew clinical cases requires the exploitation of a dedicated treatment planning system (TPS) based on theexisting version of TRiP98 [2,3], established TPS for carbon ions. The theoretical models and experimentaldatabases included in TRiP98 are presently mainly based on measurements in water. This approximationcan be applied successfully to reproduce many biological tissues with the exception of bones, where thepresence of heavy elements, like calcium, might change significantly the composition of the resultingmixed radiation field. Presently, the TriP98 physical beam model takes into account for the bone only itsdensity variation, but it neglects difference between bones and water in attenuation of the primary andproduction of secondary particles through nuclear fragmentation. However, a detailed knowledge of theparticle field at each point of the treatment area is crucial for an accurate estimate of the actual dose. Aprevious study  investigated the influence of different types of bone on the carbon particles range. Inthe present work we aim at understanding the influence of medium inhomogeneities on the 12C beam dosedistribution. For the experiment, a bone target was placed inside a water phantom. The irradiation of thetarget volume positioned partially behind the bone target and partially directly in water was simulated withTRiP98 and the dose at the interface measured at several depths along the primary beam direction. Absolutedose measurements were achieved with a system of pin-point ionization chambers, while the relative dosedistribution was investigated with two different solid states detectors: thermoluminescence detectors oftype TLD-700 and alanine ESR pellets. The position of the target volume, the thickness and the type of bone were changed to investigate the influence of the inhomogeneity in different quasi-clinical scenarios.The experimental results were compared with the values predicted by TRiP98.
|Number of pages||252|
|Publication status||Published - 2012|