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 ad-justed 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.
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%.
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