title: Clinical evaluation of X-ray voxel Monte Carlo versus pencil beam-based dose calculation in stereotactic body radiotherapy of lung cancer under normal and deep inspiration breath hold.
abstract: The purpose of this study is to evaluate the differences between dose distributions calculated with the pencil beam (PB) and X-ray voxel Monte Carlo (MC) algorithms for patients with lung cancer using intensity-modulated radiotherapy (IMRT) or HybridArc techniques. The 2 algorithms were compared in terms of dose-volume histograms, under normal and deep inspiration breath hold, and in terms of the tumor control probability (TCP). The dependence of the differences in tumor volume and location was investigated. Dosimetric validation was performed using Gafchromic EBT3 (International Specialty Products, ISP, Wayne, NJ). Forty-five Computed Tomography (CT) data sets were used for this study; 40 Gy at 8 Gy/fraction was prescribed with 5 noncoplanar 6-MV IMRT beams or 3 to 4 dynamic conformal arcs with 3 to 5 IMRT beams distributed per arc. The plans were first calculated with PB and then recalculated with MC. The difference between the mean tumor doses was approximately 10% ± 4%; these differences were even larger under deep inspiration breath hold. Differences between the mean tumor dose correlated with tumor volume and path length of the beams. The TCP values changed from 99.87% ± 0.24% to 96.78% ± 4.81% for both PB- and MC-calculated plans (P = .009). When a fraction of hypoxic cells was considered, the mean TCP values changed from 76.01% ± 5.83% to 34.78% ± 18.06% for the differently calculated plans (P < .0001). When the plans were renormalized to the same mean dose at the tumor, the mean TCP for oxic cells was 99.05% ± 1.59% and for hypoxic cells was 60.20% ± 9.53%. This study confirms that the MC algorithm adequately accounts for inhomogeneities. The inclusion of the MC in the process of IMRT optimization could represent a further step in the complex problem of determining the optimal treatment plan.
authors.affiliation: Laboratory of Medical Physics and Expert Systems, Regina Elena National Cancer Institute, Rome, Italy landoni@ifo.it.
authors.forename: V
authors.initials: V
authors.lastname: Landoni
authors.affiliation: REM Radioterapia, Catania-Istituto Oncologico del Mediterraneo (IOM), Viagrande (CT), Italy.
authors.forename: G R
authors.initials: GR
authors.lastname: Borzì
authors.affiliation: Laboratory of Medical Physics and Expert Systems, Regina Elena National Cancer Institute, Rome, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Strolin
authors.affiliation: Laboratory of Medical Physics and Expert Systems, Regina Elena National Cancer Institute, Rome, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Bruzzaniti
authors.affiliation: Laboratory of Medical Physics and Expert Systems, Regina Elena National Cancer Institute, Rome, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Soriani
authors.affiliation: Laboratory of Medical Physics and Expert Systems, Regina Elena National Cancer Institute, Rome, Italy.
authors.forename: D
authors.initials: D
authors.lastname: D'Alessio
authors.affiliation: Department of Radiation Oncology, Regina Elena National Cancer Institute, Rome, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Ambesi
authors.affiliation: REM Radioterapia, Catania-Istituto Oncologico del Mediterraneo (IOM), Viagrande (CT), Italy.
authors.forename: A M
authors.initials: AM
authors.lastname: Di Grazia
authors.affiliation: Laboratory of Medical Physics and Expert Systems, Regina Elena National Cancer Institute, Rome, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Strigari
mesh_terms: D000465:Algorithms; D062485:Breath Holding; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D009010:Monte Carlo Method; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden; D014965:X-Rays
keywords: Monte Carlo calculation; stereotactic lung radiotherapy; tumor control probability