Multimodal imaging in radiotherapy: Focus on adaptive therapy and quality control.

Improved computer resources in radiation oncology department have greatly facilitated the integration of multimodal imaging into the workflow of radiation therapy. Nowadays, physicians have highly informative imaging modalities of the anatomical region to be treated. These images contribute to the targeting accuracy with the current treatment device, impacting both segmentation or patient's positioning. Additionally, in a constant effort to deliver personalized care, many teams seek to confirm the benefits of adaptive radiotherapy. The published works highlight the importance of registration algorithms, particularly those of elastic or deformable registration necessary to take into account the anatomical evolutions of the patients during the course of their therapy. These algorithms, often considered as "black boxes", tend to be better controlled and understood by physicists and physicians thanks to the generalization of evaluation and validation methods. Given the still significant development of medical imaging techniques, it is foreseeable that multimodal registration needs require more efficient algorithms well integrated within the flow of data.

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.

[Stereotactic radiotherapy for lung cancer: Non-invasive real-time tumor tracking]. / 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.

[Repositioning accuracy of cerebral fractionated stereotactic radiotherapy using CT scanning]. / Evaluation par tomodensitométrie du repositionnement en radiothérapie stéréotaxique fractionnée cérébrale.

PURPOSE: To evaluate the accuracy of patient repositioning in fractionated cerebral stereotactic radiotherapy using a Brain Lab stereotactic cranial mask in conjunction with standard dental fixation. PATIENTS AND METHODS: Fifty planning and checking CT scans were performed in 25 patients. The check CT scan was performed before or after one of the three sessions of treatment. Coregistration to the planning CT scan was used to assess alignment of the isocentre to the reference markers. The relative position of the PTV with regard to isocentre allowed us to determine its total displacement (3D vector). RESULTS: Mean isocentre translations (+/-SD) taking into account direction were -0.01+/-0.7, -0.2+/-1.3 and 0.07+/-0.5mm in mediolateral, craniocaudal and anteroposterior directions respectively. Mean rotations (+/- SD) were -0.02+/-0.6, -0.08+/-0.3 and -0.1+/-0.3 degree in mediolateral, craniocaudal and anteroposterior axes respectively. Mean overall PTV displacement was 1.8+/-1.5mm. PTV displacement was smaller than 2 and 3mm in 19/25 and 23/25 patients respectively. CONCLUSION: The accuracy of patient positioning using a stereotactic cranial mask system is similar to those reported in the literature and shows a satisfactory reproducibility with a standard dental fixation.

[CyberKnife robotic stereotactic radiotherapy: technical aspects and medical indications]. / Radiothérapie stéréotaxique robotisée par CyberKnife : aspects techniques et indications.

In 2006, 3 sites have been selected by the Institut national of cancer (Lille, Nancy et Nice) to evaluate a radiotherapy robot, the CyberKnife. This machine, able to track mobile tumours in real time, gives new possibilities in the field of extra cranial stereotactic radiotherapy. Functionalities and medico economical issues of the machine will be evaluated during 2 years on the 3 sites.

Non-destructive 10B analysis in neutron transmission experiments.

Boron alloyed stainless-steel sheets are predominantly used in nuclear engineering as neutron shielding for radioactive waste disposal equipment. The neutron absorption depends strongly on the amount and the distribution of the 10B isotope. A systematic transmission study of 10B enriched steel plates by means of neutron time-of-flight and neutron radiography experiments was performed. The 10B content was analyzed with accuracy up to 5 x 10(-3) wt% using monochromatic beams and a linear increase of the macroscopic cross section with the 10B content was found even for strong absorbers. Then we extended the transmission analysis to "white" thermal neutron beams where large deviations from the exponential transmission law are observed. The influence of the spectral width is discussed in more detail because beam hardening causes an elevation of the effective transmission through strong absorbing materials, an effect which is crucial for the design of neutron shielding.