OBI clinical studies of setup errors in precise radiotherapy of pelvic carcinoma / 肿瘤研究与临床

ABSTRACT

Objective To study setup errors in precise radiotherapy by Varian ix accelerator OBI system and provide reference data for clinic.Methods 15 patients with pelvic cancer patients were studied in intensity modulated radiation therapy, measurement in patients with left and right (X), head and feet (Y),before and after the (Z) 3 directions respectivelY,the linear error and X,Y,Z axis to form the corresponding U, V, W rotation errors, online error correction anyway, and record the error values. The error data was analyzed before and after corrections using the two-parameter method to calculate the clinical target volume (CTV) to planning target volume (PTV) of putting boundaries (MPTV).Results 15 patients were preformed total 146 times of the first place after a and after treatment of conical CT scan,in the X,Y,Z direction system error ((x)) ± random error (s) were (1.23±0.134) mm,(2.02±7.96) mm and (1.87±3.13) mm,after treatment for respectively (0.49±1.14) mm,(0.98±2.28) mm and (1.87±3.13) mm.There was no significant difference on X direction of the tapered bed CT scan in the first place,before and after calibration,in Y and Z direction there were significant differences, corrected position error in Y and Z direction is lower compared with that of primary (P ＜ 0.05); the setup error were (0.72±1.23)°,(0.06±1.12)°,(0.12±0.97)° on U,V and W direction respectively. rotate error in general was not more than 3°. Since online correction only worked to the translation error correction, There was no difference in U,V and W before and after correction.The MPTV was 2.55,9.61 and 5.93 mm on X,Y,Z direction before correcting. Conclusions Online or offline using the OBI system to guide positioning error correction can improve the positioning accuracy and reduce the positioning uncertainty,while maintaining or increasing local control rate at the same time,reducing exposure to surrounding normal tissue,so as to improve treatment accuracy purposes.