Set-up Error in Intensity Modulated Radiotherapy for Nasopharyngeal Carcinoma
ZHAI Zhen-yu, SHEN Jun-shu, HE Xia, et al. (Jiangsu Cancer Hospital, Nanjing 210009, China)
[Purpose] To investigate the set-up error in intensity modulated radiotherapy (IMRT) with electric portal image device (EPID) in nasopharyngeal carcinoma (NPC). [Methods] Discrepancies of bone an atomy markers in various directions were achieved by comparision of digifally reconstructed radiograph (DRR) with image of EPID in 8 cases of NPC initial treated with IMRT. The maxium discrepancies in mediolateral, antero-posterior and cranio-caudal directions were defined as the set-up error of each direction. [Results] The range of set-up error in three directions was -5mm to 5.5mm. The mean set-up error in three directions was (-0.87±1.3)mm,(-0.28±1.5)mm and (-0.55±1.6)mm respectively, and errors larger than 2mm accounted for 17.3%,14.3% and 17.3% respectively. No significant difference was found in set-up error among each fraction ations. [Conclusion] The set-up error in IMRT for NPC is acceptable, and also no significant difference in every fractionations. Portal verified image in the first treatment is very important.