An assessment of the magnitude of intra-fraction movement of head-and-neck IMRT cases and its implication on the action-level of the imaging protocol

作者：Pang Pei Ping Eric^*; Hendry Julie; Cheah Shie Lee; Soong Yoke Lim; Fong Kam Weng; Wee Tien Seng Joseph; Tan Wee Kiat Terence; Nei Wen Long; Wang Fuqiang; Wong Ru Xin; Ng Wee Loon; Chen John

来源：Radiotherapy and Oncology, 2014, 112(3): 437-441.

DOI：10.1016/j.radonc.2014.09.008

• Action-level
• Imaging protocol
• Head and neck
• Intra-fraction
• Correction strategies
• Planning margins

Background and purpose: A planning margin 3 mm is employed in some head-and-neck IMRT cases due to the proximity of critical structures. This study aims to explore the need to redefine the action-level in the head-and-neck imaging protocol in consideration of the intra-fraction movement.
Material and methods: This is a local study of 18 patients treated using the same immobilisation system and setup protocol. Post-treatment orthogonal pair of kilovoltage X-ray images was acquired on the first three days of treatment. 106 sets of pre- and post-treatment kV X-ray images acquired over 53 fractions were analysed against the treatment planning DRR for calculation of intra-fraction movement.
Results: Individual mean intra-fraction movement in all directions ranged from -1.8 to 1.1 mm. Population mean (median) intra-fraction movement in the x-, y-, and z-planes were -0.1 mm (0 mm), -0.3 mm (-0.3 mm) and -0.2 mm (-0.2 mm) respectively. Intra-fraction movement in all three dimensions, x-, y- and z-planes were considered statistically significant (p < 0.05). 7 out of 53 fractions (13.2%) were highlighted as the combined magnitude of the intra-fraction motion with the uncorrected pre-treatment setup errors had exceeded the boundaries of given margins.
Conclusions: 3 mm-AL was not adequate to account for intra-fraction movement when the CTV-PTV margin was <= 3 mm and should be excluded from the routine imaging protocol and daily image-guided radiotherapy should be employed. Adjusting the action-level to 2 mm would allow a more confident approach in delivery of the prescribed dose in head-and-neck IMRT cases.

• 出版日期2014-9