ABSTRACT
Objective To investigate the positioning errors of head and neck during intensity-modulated radiation therapy of nasopharyngeal carcinoma.Methods Nineteen patients with middle-advanced nasopharyngeal carcinoma (T2-4N1-3M0), treated by intensity-modulated radiation therapy, underwent repeated CT during their 6-week treatment course.All the patients were immobilized by head-neck-shoulder thermoplastic mask.We evaluated their anatomic landmark coordinated in a total of 66 repeated CT data sets and respective x, y, z shifts relative to their position in the planning CT.ResultsThe positioning error of the neck was 2.44 mm±2.24 mm,2.05 mm±1.42 mm,1.83 mm±1.53 mm in x, y, z respectively.And that of the head was 1.05 mm±0.87 mm,1.23 mm±1.05 mm,1.17 mm±1.55 mm respectively.The positioning error between neck and head have respectively statistical difference (t=-6.58,-5.28,-3.42,P=0.000,0.000,0.001).The system error of the neck was 2.33,1.67 and 1.56 higher than that of the head, respectively in left-right, vertical and head-foot directions;and the random error of neck was 2.57,1.34 and 0.99 higher than that of head respectively.Conclusions In the process of the intensity-modulated radiation therapy of nasopharyngeal carcinoma, with the immobilization by head-neck-shoulder thermoplastic mask, the positioning error of neck is higher than that of head.
ABSTRACT
Objective To compare two verification tools for intensity modulated radiotherapy (IM-RT) and to investigate the feasibility of a new three dimensitional verification tool. Methods Five patients receiving IMRT were randomly chosen for the quality assurance plans with MapCHECK Model 1175 (SunNu-clear, Melbourne, FL,USA) and Delta4(ScandiDos, Sweden) by using Philips Pinnacle 8.0D treatment planning system. Dose verification was measured with the Varian Clinical 23EX LA. Results The overall average percentages of pass points in DD2% DTA2 mm, DD3% DTA3 mm and DD4% DTA4 mm were 84.7%, 97. 1% and 99.3% with MapCHECK Model 1175, 86.2%, 98.2% and 99.6% with Delta4 re-spectively. The differences were statisticically significant (t = 3.94, P = 0.003 ; t = 3.17, P = 0.011 ; t = 3.05 ,P =0.014,respectively). The gantry angle was changed to zero degree with MapCHECK, but not with Delta. The effects were embodied with Delta, such as the gravity on leaf position accuracy of MLC, the treat-ment table on dose distribution and the earth magnetism on dose system. Conclusion Delta4 is an ideal verification tool for intensity modulated radiotherapy.