title: The use of RapidArc volumetric-modulated arc therapy to deliver stereotactic radiosurgery and stereotactic body radiotherapy to intracranial and extracranial targets.
abstract: Twenty-three targets in 16 patients treated with stereotactic radiosurgery (SRS) or stereotactic body radiotherapy (SBRT) were analyzed in terms of dosimetric homogeneity, target conformity, organ-at-risk (OAR) sparing, monitor unit (MU) usage, and beam-on time per fraction using RapidArc volumetric-modulated arc therapy (VMAT) vs. multifield sliding-window intensity-modulated radiation therapy (IMRT). Patients underwent computed tomography simulation with site-specific immobilization. Magnetic resonance imaging fusion and optical tracking were incorporated as clinically indicated. Treatment planning was performed using Eclipse v8.6 to generate sliding-window IMRT and 1-arc and 2-arc RapidArc plans. Dosimetric parameters used for target analysis were RTOG conformity index (CI(RTOG)), homogeneity index (HI(RTOG)), inverse Paddick Conformity Index (PCI), D(mean) and D5-D95. OAR sparing was analyzed in terms of D(max) and D(mean). Treatment delivery was evaluated based on measured beam-on times delivered on a Varian Trilogy linear accelerator and recorded MU values. Dosimetric conformity, homogeneity, and OAR sparing were comparable between IMRT, 1-arc RapidArc and 2-arc RapidArc plans. Mean beam-on times ± SD for IMRT and 1-arc and 2-arc treatments were 10.5 ± 7.3, 2.6 ± 1.6, and 3.0 ± 1.1 minutes, respectively. Mean MUs were 3041, 1774, and 1676 for IMRT, 1-, and 2-arc plans, respectively. Although dosimetric conformity, homogeneity, and OAR sparing were similar between these techniques, SRS and SBRT fractions treated with RapidArc were delivered with substantially less beam-on time and fewer MUs than IMRT. The rapid delivery of SRS and SBRT with RapidArc improved workflow on the linac with these otherwise time-consuming treatments and limited the potential for intrafraction organ and patient motion, which can cause significant dosimetric errors. These clinically important advantages make image-guided RapidArc useful in the delivery of SRS and SBRT to intracranial and extracranial targets.
authors.affiliation: Department of Radiation Oncology, Chao Family Comprehensive Cancer Center, University of California, Irvine-Medical Center, Orange, CA, USA. droa@uci.edu
authors.forename: Dante E
authors.initials: DE
authors.lastname: Roa
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Schiffner
authors.forename: Juying
authors.initials: J
authors.lastname: Zhang
authors.forename: Salam N
authors.initials: SN
authors.lastname: Dietrich
authors.forename: Jeffrey V
authors.initials: JV
authors.lastname: Kuo
authors.forename: Jason
authors.initials: J
authors.lastname: Wong
authors.forename: Nilam S
authors.initials: NS
authors.lastname: Ramsinghani
authors.forename: Muthana S A L
authors.initials: MS
authors.lastname: Al-Ghazi
mesh_terms: D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008875:Middle Aged; D011874:Radiometry / Q000379:methods*; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016896:Treatment Outcome; D055815:Young Adult