ABSTRACT
Objective To measure set-up errors in intensity modulated radiotherapy of postoperative rectal cancer (IMRTPRC), and analyze the effects of target volumes and normal tissues by set-up errors in IMRTPRC. Methods electrical field device was used to measure the set-up errors of 30 patients in IMRTPRC; we randomly selected 6 patients, and simulated their radiotherapy set-up errors in TPS. Then were counted the dose distribution and analyze relative dosimetrical parameters of target volumes, normal tissues and got the set-up errors effecting on dosimetry. Statistical analysis was performed using an SPSS statistical package(Version 19.0). Results The set-up errors on X, Y and Z direction are (−0.82 ± 2.67) mm, (0.42 ± 2.91) mm and (0.47 ± 1.64) mm respectively. In regard to set-up errors of L5, R7, G8, T5, B6 and A4, most of statistical properties of PTV’s D98%, D95%, D50%, D2%, Hi and Ci are smaller than 0.05, so the differences have statistical values; In L5-Hi, G8-D2%, T5-D50% and B6-D2%, so these differences have not statistical value (P>0.05). In L5, R7, G8, T5, B6 and A4, about half of the statistical properties of normal tissue like bowl, bladder and femur heads, are smaller than 0.05 and have statistical value, and the rest of them are negative. Conclusion The dose of PTV is decreased due toset-up error. Uniformity and conformity is also gone bad. So the dosimetry quantity of PTV can not get reach to the initial design level. However, the dose of normal tissues like bowl, bladder and femur heads, are increased unexpectedly.
ABSTRACT
Objective To measure changes of definitive volume of rebuild CT image in three dimensional conformal radiotherapy (3DCRT) treatment planning system (TPS) under different scanning and observing conditions, which may provide a reference in selecting proper condition of scanning and observing, delineating target volume, and delivering treatment plan. Methods A self-made phantom was scanned under different CT scanning conditions, datas were imported to TPS, CT images were rebuilt in three dimensions under different observing conditions, and then the volumes of large, middle and small simulated tumors on CT images were compared with their real volumes. Results The volume defined by rebuilt CT imags in 3DCRT TPS varied according to different scanning and observing conditions. When scanning axial thickness was set at 10. 000 mm, errors of large, middle and small simulated tumor were - 13.60%, - 17. 68% and - 27. 53%, respectively. When 0. 625 mm was set, errors changed to -0. 50%, -0. 68% and -0. 81% ,respectively. When scanning pitch was set at 0. 562, 0. 938, 1. 375 and 1. 750, the errors were - 1.06%, - 1.09%, 5.52% and 4.75%, respectively. Extreme observing condition, window width and window level markedly increased errors of definitive volume of rebuilt CT images with a maximum of 80. 06%. Conclusions This study may provide clues in selecting scanning and observing condition, delineating target volume, and delivering treatment plan.