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Purpose The dose calculated using a convolution algorithm should be validated in a simple homogeneous water-equivalent phantom before clinical use. The dose calculation accuracy within a solid water phantom was investigated. Methods The specific Gamma knife design requires a dose rate calibration within a spherical solid water phantom. The TMR10 algorithm, which approximates the phantom material as liquid water, correctly computes the absolute dose in water. The convolution algorithm, which considers electron density miscalculates the dose in water as the phantom Hounsfield units were converted into higher electron density when the original CT calibration curve was used. To address this issue, the electron density of liquid water was affected by modifying the CT calibration curve. The absolute dose calculated using the convolution algorithm was compared with that computed by the TMR10. The measured depth dose profiles were also compared to those computed by the convolution and TMR10 algorithms. A patient treatment was recalculated in the solid-water phantom and the delivery quality assurance was checked. Results The convolution algorithm and the TMR10 calculate an absolute dose within 1% when using the modified CT calibration curve. The dose depth profile calculated using the convolution algorithms was superimposed on the TMR10 and measured dose profiles when the modified CT calibration curve was applied. The Gamma index was better than 93%. Conclusions Dose calculation algorithms, which consider electron density, require a CT calibration curve adapted to the phantom material to correctly compute the dose in water.

The new Leksell Gamma knife convolution algorithm requires evaluation prior to implementation in clinical practice. The superiority of this algorithm, which takes into account tissue electron densities, was evaluated using EBT3 GafChromicTM films within an anthropomorphic phantom. The CIRS anthropomorphic head phantom was chosen for its relevance to validate the convolution algorithm. Absolute dose and dose distributions were measured and compared with the outputs calculated from the Leksell Gamma Plan algorithms (TMR10 and the convolution algorithm). The measured absolute dose and the dose distributions in the homogeneous region of the anthropomorphic phantom were clearly in agreement with the dose distribution computed by the convolution algorithm. In a heterogeneous region where soft tissues contain a medium, such as aluminium, or an air gap, the measured dose profiles drastically changed, and only the convolution algorithm was able to correctly compute the dose to water in water. The convolution algorithm was able to take into account regions with high or very low electron densities such that the measured absolute dose was nearly equal to that computed by the convolution algorithm, with a common accepted dose measurement error of 2%.

Resume Objectif de l’etude La radiotherapie stereotaxique par CyberKnife® a ete introduite en France en 2006. Deux modes de traitement sont actuellement disponibles : l’un (Synchrony®) necessite l’implantation d’un ou de plusieurs fiduciels afin que la lesion puisse etre suivie en temps reel, l’autre (Xsight Lung Tracking System®) s’affranchit totalement de cette contrainte et permet de planifier et de realiser des traitements sans fiduciels. Patients et methodes Soixante huit patients ont ete pris en charge pour une tumeur pulmonaire entre juin 2007 et novembre 2009. A partir d’aout 2008, 26 patients ont ete traites avec l’Xsight Lung Tracking System®. Nous decrivons les conditions necessaires a la realisation de ce traitement (position, taille, lateralite de la lesion), la toxicite et les resultats de ce traitement. Resultats L’analyse a porte sur 22 patients. Le suivi etait en mediane de six mois (3–16). Le taux de controle local etait de 100 %. Le principal effet secondaire rencontre etait une pneumonie radique de grade 1 (27 %). Aucune toxicite de grade 3 ou 4 n’a ete rapportee. Conclusion Le taux de controle local eleve et la tres faible toxicite obtenue par le CyberKnife® en mode Xsight Lung® indiquent le potentiel de cette technique dans la prise en charge therapeutique des patients inoperables.

In the field of radiation oncology, equipment for fractionated radiotherapy and single-dose radiosurgery has become increasingly accurate, together with the introduction of robotized treatments. A robot is a device that can be programmed to carry out accurate, repeated and adjusted tasks in a given environment. Treatment of extracranial lesions involves taking into account organ mobility (tumor and healthy tissue) whilst retaining the ability to stereotactically locate the target. New imaging techniques (single-photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), positron emission tomography (PET)) provide further relevant information to slice images (computed tomography (CT) scans, MRI) for target definition. Hypo-fractionated treatments can only be used for curative treatment if the target is accurately defined and tracked during treatment. The CyberKnife is a non-invasive system of radiosurgery and fractionated stereotactic radiotherapy. For intracranial lesions treated by single-dose radiosurgery, it has been used to treat meningioma, acoustic neuromas, pituitary adenoma, metastases, arteriovenous malformations and refractory pain (trigeminal neuralgia). More than 10,000 patients have been treated worldwide. Currently, the most significant developments are in the field of extracranial stereotactic radiotherapy (lung, liver, reirradiation, prostate, etc.). Clinical results obtained in the CyberKnife Nord-Ouest program after 1 year of experience are presented.

National audience; En 2006, l'Institut national du cancer a lancé un appel d'offres portant sur la radiothérapie stéréotaxique extracrânienne. Trois sites (Lille, Nancy et Nice) ont été sélectionnés pour implanter et évaluer un robot de radiothérapie, le CyberKnife®. Cette machine capable de suivre des tumeurs mobiles en temps réel ouvre de nouvelles perspectives dans le champ de la radiothérapie stéréotaxique, notamment dans sa composante extracrânienne. Les fonctionnalités de cet équipement et le coût de sa mise en oeuvre vont être évalués sur une période de deux ans sur les trois sites considérés.

7050 Background: Stereotactic radiation therapy is a promising treatment for early stage lung cancer occurring in medically inoperable patients (pts). Robotic radiosurgery with the CyberKnife allow...