Analysis Of Setup Errors In The 20 Cases Pelvic Tumor By Helical Tomotherapy

[Objective] Taking advantage of helical tomotherapy (Tomo therapy) imaging guidance system to measure and analyze set-up errors of patients with pelvic tumors fixed by supine position, carbon fiber frame and thermoplastic film, and to compare differences between automatic and manual registration and calculate the margin of planning target volume of clinical target volume (CTV) and planning target volume(PTV), which provide basis for our department.[Methods] A total of 20 patients with pelvic tumors took supine position, and fixed by carbon fiber frame and thermo-plasti film, and accepted Spiral CT scanning. Images fusion and delineating target area and organ at risk were processed by Elektra Focal workstation. Radiotherapy planning was made by Tomo therapy planning station 4.0. Before each treatment, every patient accepted megavoltage cone beam CT (MVCT) and the MVCT scanning images and Standard kilovoltage CT (kVCT) images were compared in term of registration of bone landmark. Automatical and manual registration data of three direction including axis of patient from left to right(x), head to feet (y) and back to belly (z) were recorded, which got a total of 510 sets of data. All of the data was analyzed by normality test to calculate system error value (ζ) and random error value (σ) of x, y and z-axis, and to calculate the reasonable CTV—PTV margin values according to the formula of M= 2.0∑+0.7σ. Three groups registration data of autoX-manuX, autoY-manuY and autoZ-manuZ were analyzed through paired t-testing and differences were considered significant at P<0.05.[Results] All of the 20 patients have accepted 510 times MVCT scanning. And all of the registration data conformed to normal distribution, the CTV—PTV Margin values in the three directions(x, y and z) were 3.03mm,5.33mm and 2.38mm, respectively. Three groups registration data of autoX-manuX, autoY-manuY and autoZ-manuZ were analyzed through paired t-testing, and the t value were 0.325, 1.284 and 0.941, respectively, while the P value were 0.745,0.200 and 0.347, respectively,(P>0.05). There was no statistical significance between manual and automatic registration. Before Tomo radiotherapy, manual-registration didn’t have to be done every time under strict position verification.[Conclusions] In radiotherapy for pelvic tumors patients, image-guided coordination based on tomo, the CTV—PTV Margin values in the three directions(x, y and z) can be used as reference in our department, for no mage-guided department has a certain guide significance. By paired t-test and under strict position verification, manual-registration didn’t have to be done every time.