An investigation of precision of full six-degree target shift corrections using the ArcCHECK system

Objective To investigate the precision of full six-degree target shift corrections using the ArcCHECK system. Methods Fourteen patients receiving intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) in Fujian Medical University Cancer Hospital from May to September, 2015 were selected. The first treatment setup errors were obtained using cone-beam computed tomography. The setup errors were simulated in ArcCHECK, and the full six-degree target shift corrections was used to correct the errors. The plans without and with setup errors and the plan with corrected setup errors were taken. The paired t-test was used to compare dose to agreement (DTA) and Gamma passing rates between the plan without setup errors and the plan with setup errors and plan with corrected setup errors. Results The DTA and Gamma passing rates were (96.76±1.57)% and (98.35±0.92)% for the plan without setup errors, (59±21.42)% and (62.86±21.63)% for the plan with setup errors, and (91.41±4.82)% and (94.11±4.33)% for the plan with corrected setup errors. There were significant differences between the plan without setup errors and the plan with setup errors and plan with corrected setup errors in DTA passing rate (t=6.64 and 5.13, both P<0.05) and Gamma passing rate (t=6.15 and 4.19, both P<0.05). Conclusions The full six-degree target shift corrections can be used in IMRT for NPC, with good results in correcting setup errors and improving the precision for IMRT dose distribution. Key words: Nasopharyngeal neoplasm/intensity-modulated radiotherapy; Full six-degree shift corrections; Correction of error