Objective To study the accuracy of SentinelTM system for patient setup using rigid-body phantom.Methods A 002LFC IMRT phantom was placed on Elekta HexaPODTM 6-degree couch using tattoo and the laser in the treatment room.When a well-know shift (3 directions) and rotation (3 positions) was moved,CBCT and SentinelTM system were scanned respectively,and the measuring errors of six dimensions were recorded.The absolute differences between applied and measured errors were compared and paired t-test.Results Total 15 well-know shifts were investigated.The SentinelTM system was very good stability and the largest absolute difference only 0.9 mm (z direction) and 0.2° (arbitrary direction).At the same time,a good conformance between SentinelTM system and CBCT was displayed because the largest absolute difference between applied and measuring error was less than 0.9 mm (z direction) and 0.2° (arbitrary direction).Conclusions SentinelTM system is fast,simple,non-invasive and seems to be reliable in detecting patient setup errors.It maybe hold potential to ensure precise patient positioning with reduced CBCT frequency in tumor locations with fixed relation to surface structures.

Objective To investigate the effects of hippocampal?sparing intensity?modulated radiotherapy ( IMRT) on dose distribution of target volume and organs at risk ( OARs) in locally advanced nasopharyngeal carcinoma. Methods A retrospective dosimetric analysis was performed among 11 patients with locally advanced nasopharyngeal carcinoma. The MONACO ? v5. 10 Treatment Planning System was used to design three treatment plans:routine volumetric modulated arc therapy ( VMAT ) , hippocampal?sparing VMAT, and nine fixed?fields IMRT. The D98%, D50%, D2%, Dmean , conformity index ( CI ) , and homogeneity index (HI) of planning target volume (PTV) and PTVnx as well as dose distribution of the hippocampus and OARs were evaluated. Using single factor analysis of variance,two group comparative was LSD or paired t?test. Results For the above three plans,the D2% values of PTVnx were ,7 513,and 7 462 cGy,respectively (P=0. 016);the D98% values of PTV were 5837,5812,and 5914 cGy,respectively (P=0. 029);the average D2% values of PTV were 7 399,7 380,and 7 333 cGy,respectively ( P=0. 047);the HI values of PTV were 0. 239,0. 241,and 0. 220,respectively (P=0. 016);the V10 values of the brain stem were 97. 2%,88. 1%,and 90. 3%,respectively ( P=0. 001);the V20 values of the brain stem were 74. 2%, 62. 3%,and 67. 1%,respectively ( P=0. 032);the V30 values of the brain stem were 50. 9%,35. 8%,and 45. 5%, respectively ( P= 0. 020 );the V40 values of brain stem were 24. 4%, 14. 4%, and 23. 3%, respectively ( P=0. 018);the Dmean values of hippocampus were 1 518,899,and 896 cGy,respectively ( P=0. 000);the D40% values of hippocampus were 1 379,642,and 639 cGy,respectively ( P=0. 000);the V10 values of the hippocampus were 54. 1%,25. 1%,and 3. 8%,respectively ( P=0. 000);the V20 values of the hippocampus were 26. 2%, 12. 6%, and 12. 0%, respectively ( P=0. 001 ) . Conclusions Hippocampal?sparing VMAT and nine fixed?fields IMRT can significantly reduce the dose to the hippocampus without affecting dose distribution of target volume and OARs. VMAT may be superior to IMRT because VMAT can simultaneously reduce the dose to the brain stem.