A CT calibration method based on the polybinary tissue model for radiotherapy treatment planning

A method to establish the relationship between CT number and effective density for therapeutic radiations is proposed. We approximated body tissues to mixtures of muscle, air, fat, and bone. Consequently, the relationship can be calibrated only with a CT scan of their substitutes, for which we chose water, air, ethanol, and potassium phosphate solution, respectively. With simple and specific corrections for non-equivalencies of the substitutes, the calibration accuracy of 1% will be achieved. We tested the calibration method with some biological materials to verify that the proposed method would offer accuracy, simplicity, and specificity required for a standard in radiotherapy treatment planning, in particular, with heavy charged particles

Research plan of advanced patient positioning; steps toward the on-demand treatment system

NIRS-MedAustron Joint Symposium on Carbon Ion Therapy in Cance

Technical study of real time eye-motion tracking system for radiotherapy of intra-ocular tumour

To increase the accuracy and reproducibility of the patient eye-gaze and to decrease the error of dose distribution resulted from eye motion during irradiation we developed a system of real time eye-motion tracking for the particle radiotherapy of intra-ocular tumour. In almost facilities treating the intra-ocular tumors by particle beam, the patients must be capable to co-operate and to maintain to a fixed stare (gaze) at a particular angle during positioning and irradiation. An operator watches the eye motion in the monitor screen of CCD camera, and switch on the beam, or will manually switch off if patient breaks the gaze. The operator is required the instanuous interpretation to the eye motion, and this includes the time delay until beam-off with manual operation. In our developed system, the direction of the patient gaze is measured in real time using infrared video image. Two-dimensional coordinates of centres at the pupil and the Purkinje which is a reflection from the surface of cornea are determined by image processing at each field image of 16.7 milliseconds intervals. A set of these coordinates is applied to the geometrical eye model, and the angle of gaze in spatial coordinate is calculated. This estimated gaze direction is compared with previously set angle that is clinically admissible gaze motion. If the direction of gaze changes to outside of the admission or by the blink, the irradiation is automatically turned off thorough the gate signal (TTL) for beam extraction. In preliminary study using an artificial eye, our system detected the position variation of 0.2 mm, and in subjects study, detected the gaze variation of 1.8 degree that is almost equivalent to the variation of 0.4 mm on the eye surface. The total response time from the change of gaze to TTL-off was less than 67 milliseconds. This system will support the safety irradiation of ocular tumour.40th　PTCO

New treatment facility for heavy-ion radiation therapy at HIMAC

Heavy ions in therapy and space symposiu

A REAL TIME EYE-MOTION TRACKING SYSTEM FOR IMAGE GUIDED RADIOTHERAPY OF INTRA-OCULAR TUMOR

During the irradiation of the intra-ocular tuomur, the patient must be capable to co-operate and to maintain to a fixed stare at a particular angle to concentrate the dose on the target. To increase the accuracy and reproducibility of the gaze and to avoid the error of dose distribution resulted from eye-motion, we developed a system to track the eye-motion in real time and to irradiate with the gating technique. Using infrared video image around the patient eye, the pupil and the Purkinje which is a reflection from the surface of cornea are detected by image processing. A set of these two points is applied on the eye-ball model and the angle of gaze is estimated. If the direction of gaze is moved to outside of permitted area by the rotary motion of eye ball or by the eyelid, the gate signal to beam-off is generated, and the irradiation is automatically turned off. In preliminary study using an artificial eye, our system detected the pupil position with the accuracy of less than 0.2 mm. In subjects, the minor fluctuation about 1.8 degree of the gaze direction was observed. This variation was almost equivalent to the motion of 0.4 mm on the eye surface. The total response time from the change of gaze to beam-off was less than 67 milliseconds. The accuracy of developed system would be enough clinically, and this will support the safety irradiation of ocular tumour and the quantitative verification of the patient gaze.4th Shinji Takahashi Memorial International Workshop on 3D-CR

Dose Distribution of Heavy-ion Scanning Irradiationfor Simulated for Moving Target

Objective:Heavy ion radiotherapy is characterized its excellent physical dose localization and the biological effectiveness because of its high linear energy transfer (LET). The scanning irradiation of heavy ion, which is the highly conformal techniques, is more sensitive to motion effects. The consequence can be under-dosage of the target volume or over-dosage of critical structures. The effectiveness of scanning irradiation with the respiratory-gated techniques for the moving target is evaluated in this study.Material and Methods:The scanning irradiation using carbon ions is planed to the target contours on a set of 3D CT images. They are converted to the water equivalent depth coordinate and the prescribed dose is set in and around the target region. The Bragg peaks of beams are arranged in the water equivalent space, and the weight of each beam spot is optimized to meet the condition of the prescribed dose. From the optimized beam arrangement and the weight, the planned dose distribution is calculated and displayed on the axial, sagittal, or coronal multiplanar reconstruction CT image. The motion models are constructed based on a set of sequential 3D CT volume (4D CT) data of various clinical cases, such as lung and liver tumor. And the dose distribution simulated for the moving target is evaluated with this model. Results:The scanning-irradiated dose distribution is simulated for the clinical targets based on the motion analysis of tumor. The motion of tumor is analyzed by the direction, distance, speed and variation of density. Especially for the heavy-ion radiotherapy, the density through beam path is crucial because it affects strongly on the dose coverage around the distal end of the tumor. For some clinical moving models, the dose uniformities in planning target volume and the outer dosage on normal tissue are estimated with the timing for respiration. The quantitative analysis with the scanning parameters such as beam size, arrangement and scanning speed, is on going.Conclusion:This simulation of scanning irradiation enables the clinical evaluation of the dose distribution for the moving target. The effect on dose uniformity is estimated and the engineering requirements for the scanning devices can be examined to the tumor on moving target.Third International Conference on Translational Research and Pre-Clinical Stratgies in Radiation Oncolog

Quantitative Evaluation of 3D Lung Motion with Anatomical Feature Tracking Technique for Precise Particle Radiotherapy

ICTR２００６（Third International Conference on Translational Research and Pre-Clinical Strategies in Radiation Oncology

Visualization of dose distribution on the endobronchial surface using virtual bronchoscopy

ICTR２００６（Third International Conference on Translational Research and Pre-Clinical Strategies in Radiation Oncology