title: An assessment of interfractional bladder, rectum and vagina motion in postoperative cervical cancer based on daily cone-beam computed tomography.
abstract: Interfractional variations of the bladder, rectum and vagina may affect the accuracy of postoperative intensity-modulated radiotherapy in patients with cervical cancer. This study aimed to assess the interfractional variations with daily kV cone-beam computed tomography (CBCT). All the patients were instructed to control the filling status of the bladder and rectum. CBCT images were obtained daily after set-up and the bladder, rectum and vagina were contoured on each CBCT scan. All the contours were transferred to the planning CT following image fusion. Interfractional variations in pelvic organs were assessed with CBCT based on two reference lines, which were identified as A (the midsaggital line across the superior border of pubic symphysis) and B (a parallel line 1.5 cm above line A). The mean volume (range) of the bladder and rectum was 156.5 (1.7-626.5) and 48.2 (11.3-139.7) ml, respectively. The uniform planning target volume (PTV) margin of 10 mm failed to encompass the vagina in 17.3 and 18.1% of the fractions on lines A and B, respectively. The motion of the vagina (standard deviation) was 0.3 (0.3) and 0.1 (0.5) cm on lines A and B, respectively. The anteroposterior dimension and position of the vagina were significantly affected by the filling status of the bladder (P<0.05), but not by that of the rectum. Although instructions were given, the interfractional variations of the vagina and other pelvic organs were significant, which may exceed the uniform PTV margin; therefore, more effective methods to decrease these variations should be investigated.
authors.affiliation: Department of Radiation Oncology, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China.
authors.forename: Xin
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China.
authors.forename: Min
authors.initials: M
authors.lastname: Yu
authors.affiliation: Department of Radiation Oncology, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China.
authors.forename: Jin
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China.
authors.forename: Renming
authors.initials: R
authors.lastname: Zhong
authors.affiliation: Department of Radiation Oncology, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China.
authors.forename: Yali
authors.initials: Y
authors.lastname: Shen
authors.affiliation: Department of Radiation Oncology, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China.
authors.forename: Yaqin
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Department of Radiation Oncology, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China.
authors.forename: Zhiping
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Radiation Oncology, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China.
authors.forename: Sen
authors.initials: S
authors.lastname: Bai
authors.affiliation: Department of Radiation Oncology, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China.
authors.forename: Feng
authors.initials: F
authors.lastname: Xu
keywords: cone-beam computed tomography; intensity-modulated radiotherapy; organ motion; postoperative cervical cancer; vagina motion