title: Investigation of linac-based image-guided hypofractionated prostate radiotherapy.
abstract: A hypofractionation treatment protocol for prostate cancer was initiated in our department in December 2003. The treatment regimen consists of a total dose of 36.25 Gy delivered at 7.25 Gy per fraction over 10 days. We discuss the rationale for such a prostate hypofractionation protocol and the need for frequent prostate imaging during treatment. The CyberKnife (Accuray Inc., Sunnyvale, CA), a linear accelerator mounted on a robotic arm, is currently being used as the radiation delivery device for this protocol, due to its incorporation of near real-time kV imaging of the prostate via 3 gold fiducial seeds. Recently introduced conventional linac kV imaging with intensity modulated planning and delivery may add a new option for these hypofractionated treatments. The purpose of this work is to investigate the use of intensity modulated radiotherapy (IMRT) and the Varian Trilogy Accelerator with on-board kV imaging (Varian Medical Systems Inc., Palo Alto, CA) for treatment of our hypofractionated prostate patients. The dose-volume histograms and dose statistics of 2 patients previously treated on the CyberKnife were compared to 7-field IMRT plans. A process of acquiring images to observe intrafraction prostate motion was achieved in an average time of about 1 minute and 40 seconds, and IMRT beam delivery takes about 40 seconds per field. A complete 7-field IMRT plan can therefore be imaged and delivered in 10 to 17 minutes. The Varian Trilogy Accelerator with on-board imaging and IMRT is well suited for image-guided hypofractionated prostate treatments. During this study, we have also uncovered opportunities for improvement of the on-board imaging hardware/software implementation that would further enhance performance in this regard.
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305-5847, USA. tpaw@stanford.edu
authors.forename: Todd
authors.initials: T
authors.lastname: Pawlicki
authors.forename: Gwe-Ya
authors.initials: GY
authors.lastname: Kim
authors.forename: Annie
authors.initials: A
authors.lastname: Hsu
authors.forename: Cristian
authors.initials: C
authors.lastname: Cotrutz
authors.forename: Arthur L
authors.initials: AL
authors.lastname: Boyer
authors.forename: Lei
authors.initials: L
authors.lastname: Xing
authors.forename: Christopher R
authors.initials: CR
authors.lastname: King
authors.forename: Gary
authors.initials: G
authors.lastname: Luxton
mesh_terms: D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D010315:Particle Accelerators / Q000295:instrumentation*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation* / Q000379:methods; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000295:instrumentation