Speaker
Description
Carbon ion radiotherapy is an effective radiotherapy with a high linear energy transfer (LET) and a sharp dose distribution. Nevertheless, carbon ion medical accelerators are larger than medical proton accelerators and are difficult to construct and maintain. In particular, a rotating gantry is preferable for patient treatment, but this had not been realized for a long time due to its large size and weight.
Recently, compact rotating gantries using superconducting magnets have been developed and are now in operation at several facilities. Since the gantries have a heavy weight of about 200 tons and have not only long power cables but also many metallic flexible transfer hoses for liquid helium from cryocooler compressors, mechanical troubles are unavoidable. There were, however, not enough experience of mechanical troubles in the accelerator society. Sharing the experience will help new users of medical accelerators.
East Japan Heavy Ion Center, Faculty of Medicine, Yamagata University started treatment operation in 2021. Overall machine availability for total system (accelerator, fixed port room, and gantry room) is 96.5% and more than 3,000 patients have been treated. In this facility. a superconducting rotating gantry has been successfully operated with no long-term treatment delay. In We introduce major troubles with the rotating gantry below:
* Superconducting magnet displacement causing beam orbit distortion
* Water leak from flexible hose
* Deformation of flexible hose
* Damage to the cryocooler power cable result in earth fault
Details, root cause analysis, and reactions to prevent recurrence of these troubles will be presented.