Francois Dubus

Extracranial Stereotactic Radiotherapy: Preliminary Results with the CyberKnife®

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.

Radiothérapie stéréotaxique de carcinomes bronchiques primitifs: suivi non invasif de la cible en temps réel

PURPOSE Stereotactic radiation therapy using the CyberKnife(®) has been introduced in France in 2006. Two treatment modalities are currently available: the first one (Synchrony(®)) is a real-time fiducial-based target tracking system, while the other (Xsight Lung Tracking [XLT] System(®)) is completely fiducial-free. PATIENTS AND METHODS Sixty-eight patients were treated for a pulmonary tumor between June 2007 and November 2009. Since august 2008, the XLT System(®) was used for 26 patients. We report the necessary conditions for the XLT System (position, laterality and size of the tumor), the toxicity and outcome of this treatment. RESULTS Twenty-two patients were analyzed. Median follow-up was 6 months (min=3; max=16). Local control rate was 100%. The main toxicity was grade grade 1 pulmonary alveolitis (27%). No grade 3 or 4 toxicities were reported. CONCLUSION The high local control rate and low toxicity obtained with the CyberKnife(®) XLT System(®) suggest that such treatment is an alternative for inoperable patients.

Clinical implementation of a Monte Carlo based treatment plan QA platform for validation of Cyberknife and Tomotherapy treatments

PURPOSE The main focus of the current paper is the clinical implementation of a Monte Carlo based platform for treatment plan validation for Tomotherapy and Cyberknife, without adding additional tasks to the dosimetry department. METHODS The Monte Carlo platform consists of C++ classes for the actual functionality and a web based GUI that allows accessing the system using a web browser. Calculations are based on BEAMnrc/DOSXYZnrc and/or GATE and are performed automatically after exporting the dicom data from the treatment planning system. For Cyberknife treatments of moving targets, the log files saved during the treatment (position of robot, internal fiducials and external markers) can be used in combination with the 4D planning CT to reconstruct the actually delivered dose. The Monte Carlo platform is also used for calculation on MRI images, using pseudo-CT conversion. RESULTS For Tomotherapy treatments we obtain an excellent agreement (within 2%) for almost all cases. However, we have been able to detect a problem regarding the CT Hounsfield units definition of the Toshiba Large Bore CT when using a large reconstruction diameter. For Cyberknife treatments we obtain an excellent agreement with the Monte Carlo algorithm of the treatment planning system. For some extreme cases, when treating small lung lesions in low density lung tissue, small differences are obtained due to the different cut-off energy of the secondary electrons. CONCLUSIONS A Monte Carlo based treatment plan validation tool has successfully been implemented in clinical routine and is used to systematically validate all Cyberknife and Tomotherapy plans.

Radiothérapie stéréotaxique extracrânienne: la place du CyberKnife®

RésuméEn 2006, l’Institut national du cancer a lancé un appel d’offres portant sur la radiothérapie stéréotaxique extracrânienne. Trois sites 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 œuvre vont ètre évalués sur une période de deuxanssur les trois sites considérés.AbstractIn 2006, three sites were selected by the French Institut national du cancer to evaluate the CyberKnife robotic radiotherapy system. This device, able to track mobile tumours in real time, offers new possibilities in the field of extracranial stereotactic radiotherapy. The device’s functionalities, as well as medical and economical issues, will be evaluated for two years on the three sites.

Abstract ID: 222 Clinical implementation of a Monte Carlo based QA platform for validation of Tomotherapy and Cyberknife treatment plans

INTRODUCTION This work describes the clinical implementation of a Monte Carlo based platform for treatment plan validation for Tomotherapy and Cyberknife, including a semi-automatic plan evaluation module based on dose constraints for organs-at-risk (OAR). METHODS The Monte Carlo-based platform Moderato [1] is based on BEAMnrc/DOSXYZnrc and allows for automated re-calculation of doses planned with Tomotherapy and Cyberknife techniques. The Prescription/Validation module generates a set of dose constraints based on the anatomical region and fractionation scheme considered. Upon achievement of the planning, dose results are displayed with visual warnings in case of constraint violation. The system was tested on 83 patient cases in order to evaluate the influence of difference in calculation algorithms on OAR constraints. RESULTS The first results with the Tomotherapy plans allowed for detecting and correcting a problem with the CT Hounsfield units when using a large reconstruction diameter (a CT artifact that lead to air voxels with an overestimated density). The Cyberknife results also showed some dose differences associated with different energy thresholds between Moderato and the Monte Carlo algorithm used in the Treatment Planning Station. Regarding OAR constraints, re-calculation generated few violations in thoracic, pelvic and abdominal cases. However, in spinal and head cases, significant differences can appear (-11% to +6%) on optic pathways and spinal cord, leading to doses above the limits. CONCLUSIONS The Moderato platform constitutes a promising tool for the validation of plan quality, offering both dose re-calculation and OAR constraints evaluation. First results show the importance of this verification for some specific regions. Further work is ongoing to optimize the quantity and relevance of the information displayed, before fully introducing the system in clinical routine.