Presentation First experiences for respiratory gating carbon-ion scanning therapy using marker-less tumor tracking

森, 慎一郎

In 2011, we started carbon-ion scanning beam therapy for limited anatomical sites not requiring respiratory gating. And now overall room occupation time (from entering to leaving the treatment room) was 10 minutes in average. We have been preparing to provide respiratory gating scanning treatment, because it is well known that pencil beam scanning offers excellent dose conformity, but is sensitive to organ motion. Therefore, we developed and integrated several motion compensating techniques to gated treatment; phase-control, rescanning, amplitude-based gating. Of-course, all clinical work-flow is generated based on 4D imaging. Here, we introduced our first experiences for scanning beam therapy in thoracic and abdominal regions.A few cases of lung and liver cancer patients selected from inpatients at our hospital. 4DCT was done with the 320 multi-slice CT under free-breathing conditions. Radiation oncologists input the target and normal tissue contours on the reference phase. To calculate range-ITV, beam ranges were calculated from the beam entrance of the patient surface to the distal and proximal edge of the target for the respective phases. The range-ITV was then calculated by selecting the minimum and maximum beam ranges ray-by-ray. Gating window was defined as 50% peri-exhale (T30-T70), the prescribed dose was 60Gy(RBE) and 45 Gy(RBE) for lung and liver treatments, respectively. Over 6 times phase-controlled rescanning was applied to minimize interplay effect. We have installed an X-ray fluoroscopic imaging system in our treatment room for clinical use with an amplitude-based gating strategy. Use of an implanted fiducial marker strongly facilitates the detection of tumor position, but is somewhat invasive due to the risk of pneumothorax on insertion and cannot be used in all patients due to patient condition. We, therefore, generated real time marker-less tumor tracking to turn on/off treatment beam.
Particle Therapy Co-Operative Group

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