title: Inter-Fraction Tumor Volume Response during Lung Stereotactic Body Radiation Therapy Correlated to Patient Variables.
abstract: OBJECTIVE
  Analyze inter-fraction volumetric changes of lung tumors treated with stereotactic body radiation therapy (SBRT) and determine if the volume changes during treatment can be predicted and thus considered in treatment planning.
  
  
  METHODS
  Kilo-voltage cone-beam CT (kV-CBCT) images obtained immediately prior to each fraction were used to monitor inter-fraction volumetric changes of 15 consecutive patients (18 lung nodules) treated with lung SBRT at our institution (45-54 Gy in 3-5 fractions) in the year of 2011-2012. Spearman's (ρ) correlation and Spearman's partial correlation analysis was performed with respect to patient/tumor and treatment characteristics. Multiple hypothesis correction was performed using False Discovery Rate (FDR) and q-values were reported.
  
  
  RESULTS
  All tumors studied experienced volume change during treatment. Tumor increased in volume by an average of 15% and regressed by an average of 11%. The overall volume increase during treatment is contained within the planning target volume (PTV) for all tumors. Larger tumors increased in volume more than smaller tumors during treatment (q = 0.0029). The volume increase on CBCT was correlated to the treatment planning gross target volume (GTV) as well as internal target volumes (ITV) (q = 0.0085 and q = 0.0039 respectively) and could be predicted for tumors with a GTV less than 22 mL. The volume increase was correlated to the integral dose (ID) in the ITV at every fraction (q = 0.0049). The peak inter-fraction volume occurred at an earlier fraction in younger patients (q = 0.0122).
  
  
  CONCLUSIONS
  We introduced a new analysis method to follow inter-fraction tumor volume changes and determined that the observed changes during lung SBRT treatment are correlated to the initial tumor volume, integral dose (ID), and patient age. Furthermore, the volume increase during treatment of tumors less than 22mL can be predicted during treatment planning. The volume increase remained significantly less than the overall PTV expansion, and radiation re-planning was therefore not required for the purpose of tumor control. The presence of the studied correlations suggests that the observed volumetric changes may reflect some underlying biologic process rather than random fluctuations.
authors.affiliation: Department of Radiation Oncology, The Ohio State University Wexner Medical Center, Columbus, Ohio, United States of America.
authors.forename: Samer
authors.initials: S
authors.lastname: Salamekh
authors.affiliation: Department of Radiation Oncology, University of California Davis, Sacramento, California, United States of America.
authors.forename: Yi
authors.initials: Y
authors.lastname: Rong
authors.affiliation: Department of Radiation Oncology, The Ohio State University Wexner Medical Center, Columbus, Ohio, United States of America.
authors.forename: Ahmet S
authors.initials: AS
authors.lastname: Ayan
authors.affiliation: Center for Biostatistics, The Ohio State University Wexner Medical Center, Columbus, Ohio, United States of America.
authors.forename: Xiaokui
authors.initials: X
authors.lastname: Mo
authors.affiliation: Department of Radiation Oncology, The Ohio State University Wexner Medical Center, Columbus, Ohio, United States of America.
authors.forename: Terence M
authors.initials: TM
authors.lastname: Williams
authors.affiliation: Department of Radiation Oncology, University of Washington, Seattle, Washington, United States of America.
authors.forename: Nina A
authors.initials: NA
authors.lastname: Mayr
authors.affiliation: Department of Radiation Oncology, The Ohio State University Wexner Medical Center, Columbus, Ohio, United States of America.
authors.forename: John C
authors.initials: JC
authors.lastname: Grecula
authors.affiliation: Department of Radiation Oncology, The Ohio State University Wexner Medical Center, Columbus, Ohio, United States of America.
authors.forename: Arnab
authors.initials: A
authors.lastname: Chakravarti
authors.affiliation: Department of Radiation Oncology, The Ohio State University Wexner Medical Center, Columbus, Ohio, United States of America.
authors.forename: Meng
authors.initials: M
authors.lastname: Xu-Welliver
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D054893:Cone-Beam Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D008875:Middle Aged; D016634:Radiosurgery