Purpose: Megavoltage CT (MVCT) study on helical tomotherapy permits to verify and correct the patient setup by coregistration with the planning kVCT. This process is time-consuming and our objective is to investigate a possibility of using a smaller number of imaging studies in the case of patients with prostate cancer.
Patients and methods: The interfraction shifts of 20 patients (about 700 MVCT studies) treated in our institution have been recorded and analyzed. A new reference position has been calculated as an average of shifts observed during different initial number of fractions imaged.
Results: The analysis of the reference position obtained for the set of 20 patients as a function of the number of imaging sessions has shown that MVCT studies during first four fractions are sufficient for the majority of patients.
Conclusion: Imaging during the first four fractions can be used to determine a reference position for patients with prostate cancer treated on helical tomotherapy. A study on Planned Adaptive (TomoTherapy Inc., Madison, WI, USA) software to evaluate the clinical significance of this scenario is currently in process in our institution.