title: Tumor control probability and the utility of 4D vs 3D dose calculations for stereotactic body radiotherapy for lung cancer.
abstract: Four-dimensional (4D) dose calculations for lung cancer radiotherapy have been technically feasible for a number of years but have not become standard clinical practice. The purpose of this study was to determine if clinically significant differences in tumor control probability (TCP) exist between 3D and 4D dose calculations so as to inform the decision whether 4D dose calculations should be used routinely for treatment planning. Radiotherapy plans for Stage I-II lung cancer were created for 8 patients. Clinically acceptable treatment plans were created with dose calculated on the end-exhale 4D computed tomography (CT) phase using a Monte Carlo algorithm. Dose was then projected onto the remaining 9 phases of 4D-CT using the Monte Carlo algorithm and accumulated onto the end-exhale phase using commercially available deformable registration software. The resulting dose-volume histograms (DVH) of the gross tumor volume (GTV), planning tumor volume (PTV), and PTVsetup were compared according to target coverage and dose. The PTVsetup was defined as a volume including the GTV and a margin for setup uncertainties but not for respiratory motion. TCPs resulting from these DVHs were estimated using a wide range of alphas, betas, and tumor cell densities. Differences of up to 5Gy were observed between 3D and 4D calculations for a PTV with highly irregular shape. When the TCP was calculated using the resulting DVHs for fractionation schedules typically used in stereotactic body radiation therapy (SBRT), the TCP differed at most by 5% between 4D and 3D cases, and in most cases, it was by less than 1%. We conclude that 4D dose calculations are not necessary for most cases treated with SBRT, but they might be valuable for irregularly shaped target volumes. If 4D calculations are used, 4D DVHs should be evaluated on volumes that include margin for setup uncertainty but not respiratory motion.
authors.affiliation: Department of Radiation Oncology, Perelman Center for Advanced Medicine, University of Pennsylvania, Philadelphia, PA. Electronic address: gilmer.valdes@uphs.upenn.edu.
authors.forename: Gilmer
authors.initials: G
authors.lastname: Valdes
authors.affiliation: Department of Radiation Oncology, Siteman Cancer Center, Washington University in St. Louis, St. Louis, MO.
authors.forename: Clifford
authors.initials: C
authors.lastname: Robinson
authors.affiliation: Department of Radiation Oncology, David Geffen School of Medicine, UCLA, Los Angeles, CA.
authors.forename: Percy
authors.initials: P
authors.lastname: Lee
authors.affiliation: Department of Biomedical Engineering, AIX Marseille 2 University, Marseille, France; Department of Medical Physics, Joseph Fourier University, Grenoble, France.
authors.forename: Delphine
authors.initials: D
authors.lastname: Morel
authors.affiliation: Department of Radiation Oncology, David Geffen School of Medicine, UCLA, Los Angeles, CA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Low
authors.affiliation: Department of Radiation Oncology, David Geffen School of Medicine, UCLA, Los Angeles, CA.
authors.forename: Keisuke S
authors.initials: KS
authors.lastname: Iwamoto
authors.affiliation: Department of Radiation Oncology, David Geffen School of Medicine, UCLA, Los Angeles, CA.
authors.forename: James M
authors.initials: JM
authors.lastname: Lamb
mesh_terms: D003198:Computer Simulation; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000601:surgery*; D015233:Models, Statistical; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016896:Treatment Outcome; D047368:Tumor Burden / Q000528:radiation effects
keywords: 3D dose calculations; 4D dose calculations; TCP