Backgrounds:The first Proton Beam Therapy (PBT) system, which has gated spot scanning with real-time tumor-tracking, has been developed and is now under operation. The new system enables us to deliver highly conformal dose to the moving target tumors while sparing surrounding healthy tissues by integrating real-time tumor-tracking and discrete spot scanning techniques. The system is designed to be spot scanning dedicated in order to maximize the efficiency of proton beam utilization and minimize the size of system and facility.
The newly designed system consists of a synchrotron, beam transport systems, a compact rotating gantry system with robotic couch and two orthogonal sets of X-ray fluoroscopes. The system has the ability to control dose distribution with spot scanning beams and to gate the beams from the synchrotron to irradiate a moving target tumor only when the actual positions of fiducial markers are within the planned positions. The new sophisticated synchrotron control system enables multiple-gated irradiations per operation cycle according to the gating signals of the real-time tumor-tracking system. Investigation has been made to minimize motion dose errors and irradiation times. Both treatment accuracy and efficiency were improved significantly in the new system. Researches for Cone-Beam CT and four-dimensional treatment planning system are work-in-progress to maximize its clinical usefulness.
The PBT center started patient treatment in March 2014. Commissioning of the system was finished in November and gated spot scanning treatment has been started from December 2014. Several patients with prostate and liver cancer have been successfully treated. The real-time tumor-tracking system has been demonstrated accurate doze distributions for moving target tumors.
The new capability of the PBT for moving tumors has been realized by using the gated spot scanning with real-time tumor-tracking system. The system will deliver significant advantages for both clinical and economical points of view.