title: Influence of different treatment techniques and clinical factors over the intrafraction variation on lung stereotactic body radiotherapy.
abstract: OBJECTIVE
  In the present study we compared three different Stereotactic body radiation therapy (SBRT) treatment delivery techniques in terms of treatment time (TT) and their relation with intrafraction variation (IFV). Besides that, we analyzed if different clinical factors could have an influence on IFV. Finally, we appreciated the soundness of our margins.
  
  
  METHODS
  Forty-five patients undergoing SBRT for stage I lung cancer or lung metastases up to 5 cm were included in the study. All underwent 4DCT scan to create an internal target volume (ITV) and a 5 mm margin was added to establish the planning target volume (PTV). Cone-beam CTs (CBCTs) were acquired before and after each treatment to quantify the IFV. Three different treatment delivery techniques were employed: fixed fields (FF), dynamically collimated arcs (AA) or a combination of both (FA). We studied if TT was different among these modalities of SBRT and whether TT and IFV were correlated. Clinical data related to patients and tumors were recorded as potential influential factors over the IFV.
  
  
  RESULTS
  A total of 52 lesions and 147 fractions were analyzed. Mean IFV for x-, y- and z-axis were 1 ± 1.16 mm, 1.29 ± 1.38 mm and 1.17 ± 1.08 mm, respectively. Displacements were encompassed by the 5 mm margin in 96.1 % of fractions. TT was significantly longer in FF therapy (24.76 ± 5.4 min), when compared with AA (15.30 ± 3.68 min) or FA (17.79 ± 3.52 min) (p < 0.001). Unexpectedly, IFV did not change significantly between them (p = 0.471). Age (p = 0.003) and left vs. right location (p = 0.005) were related to 3D shift ≥2 mm. In the multivariate analysis only age showed a significant impact on the IFV (OR = 1.07, p = 0.007).
  
  
  CONCLUSIONS
  The choice of AA, FF or FA does not impact on IFV although FF treatment takes significantly longer treatment time. Our immobilization device offers enough accuracy and the 5 mm margin may be considered acceptable as it accounts for more than 95 % of tumor shifts. Age is the only clinical factor that influenced IFV significantly in our analysis.
authors.affiliation: Department of Radiation Oncology, Complejo Hospitalario de Navarra, Pamplona, Spain. lekimrico@hotmail.com.
authors.forename: M
authors.initials: M
authors.lastname: Rico
authors.affiliation: Department of Radiation Oncology, Complejo Hospitalario de Navarra, Pamplona, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Martínez
authors.affiliation: Department of Radiation Physics, Complejo Hospitalario de Navarra, Pamplona, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Pellejero
authors.affiliation: Department of Preventive Medicine, Complejo Hospitalario de Navarra, Pamplona, Spain.
authors.forename: B
authors.initials: B
authors.lastname: Bermejo
authors.affiliation: Department of Radiation Oncology, Complejo Hospitalario de Navarra, Pamplona, Spain.
authors.forename: P
authors.initials: P
authors.lastname: Navarrete
authors.affiliation: Department of Radiation Oncology, Complejo Hospitalario de Navarra, Pamplona, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Barrado
authors.affiliation: Department of Radiation Oncology, Complejo Hospitalario de Navarra, Pamplona, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Campo
authors.affiliation: Department of Radiation Physics, Complejo Hospitalario de Navarra, Pamplona, Spain.
authors.forename: F
authors.initials: F
authors.lastname: Mañeru
authors.affiliation: Department of Radiation Oncology, Complejo Hospitalario de Navarra, Pamplona, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Villafranca
authors.affiliation: Department of Radiation Oncology, Clínica Universidad de Navarra, Pamplona, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Aristu
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D019583:Dose Fractionation, Radiation; D005260:Female; D005500:Follow-Up Studies; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011379:Prognosis; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors / Q000517:prevention & control; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D047368:Tumor Burden
keywords: Clinical factors; Intrafraction variation; Lung SBRT; Treatment delivery technique; Treatment time