【Objective】To explore the different scanning frequency for the MVCT scanning in the tomotherapy

and seek the best strategy of the scanning.【Methods】Patients were treated by tomotherapy in SYSUCC from January 1

2015 to May 15

2016

includ? ing 88 head & neck patients

63 chest & abdomen patients and 19 pelvis patients. All patients have had a daily MVCT scanning for po? sition verification before the treatment. The data retrieved from“the first five times of the very first week”and“the every first time of each week”

were compared with“the whole course”data

respectively.【Results】There are no significant difference between“the whole course”and“the first five times of the very first week”or“the every first time of each week”for pelvis patients and chest and abdomen patients. There are significant differences between Z axis of“the whole course”and“the first five times of the very first week”only for head & neck patients.【Conclusion】It is a good scanning choice of“the first five times of the very first week”and“the every first time of each week”for the those patients with thoracic & abdominal or pelvic tumors to reduce the extra radiation dose from the MVCT. There are significant differences between Z axis of“the whole course”and“the first five times of the very first week”in the head & neck patients. Therefore

“the first five times of the very first week”cannot be used as a solid position information for daily verification. And“the every first time of each week”may be a good compromise solution.