title: Effect of intrafractional prostate motion on simultaneous boost intensity-modulated radiotherapy to the prostate: a simulation study based on intrafractional motion in the prone position.
abstract: Although the prostate displacement of patients in the prone position is affected by respiration-induced motion, the effect of intrafractional prostate motion in the prone position during "simultaneous integrated boost intensity-modulated radiotherapy" (SIB-IMRT) is unclear. The purpose of this study was to evaluate the dosimetric effects of intrafractional motion on SIB-IMRT to a dominant intraprostatic lesion (IPL) using measured motion data of patients in a prone position, fixed with a thermoplastic shell. We obtained 2 orthogonal x-ray fluoroscopic images at the same moment every 0.2 seconds for 30 seconds before and after treatment, once weekly, from 7 patients with localized prostate cancer with detectable prostatic calcification. Prostate displacements in the left-right (LR), anteroposterior (AP), and superoinferior (SI) directions were calculated using the prostatic calcification as a fiducial marker. We defined the displacement between pretreatment and posttreatment as baseline drift (BD). An SIB-IMRT plan was generated in which each IPL + 3mm received a dose of 94.5Gy, whereas the remainder of the prostate + 7mm received a dose of 75.6Gy in 9 fields. A simulated plan of dose blurring was generated by the convolution of isocenter-shifted plans using measured motion data in 30 seconds and motion in 30 seconds + distance between pretreatment and posttreatment position (BD) for each of the 7 patients. The motion in 30 seconds mainly reflected respiration-induced motion. The mean displacements of BD were 1.4mm (- 3.1 to 8.2mm), - 2.2mm (- 9.1 to 1.5mm), and - 0.3mm (- 5.0 to 1.8mm) in the AP, SI, and LR directions, respectively. The differences in the target coverage with V90% of the IPL and V100% of the prostate between the simulated plan and original plan were - 3.9% to - 0.3% and - 0.6% to 1.1% for respiration-induced motion and 3.1% to - 67.8% and 3.6% to - 13.3% for BD with respiration-induced motion, respectively. The large motion of BD resulted in an inadequate coverage by the prescribed dose of the SIB-IMRT to the IPL. A 7-mm margin is recommended when real-time tracking techniques are not applied. The effect of respiration-induced motion was small, so long as a 3-mm margin was added.
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University Kyoto, Japan.
authors.forename: Itaru
authors.initials: I
authors.lastname: Ikeda
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University Kyoto, Japan. Electronic address: mizo@kuhp.kyoto-u.ac.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Mizowaki
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University Kyoto, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Ono
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University Kyoto, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Yamada
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University Kyoto, Japan.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University Kyoto, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Monzen
authors.affiliation: Division of Clinical Radiology Service, Kyoto University Hospital, Kyoto, Japan.
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Yano
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University Kyoto, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hiraoka
mesh_terms: D003198:Computer Simulation; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D009068:Movement; D016684:Prone Position; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D050397:Radiotherapy, Intensity-Modulated
keywords: Intensity-modulated radiotherapy; Intrafractional motion; Prone position; Prostate cancer; Simulation