title: Image-guided radiotherapy for prostate cancer using 3 different techniques: localization data of 186 patients.
abstract: OBJECTIVE
  This study evaluates 3 different imaging modalities--ultrasound (US), stereoscopic X-ray imaging of implanted markers (Visicoils) (X-ray), and kV cone-beam computed tomography (CBCT)--to assess interfraction and intrafraction localization error during conformal radiation therapy of prostate cancer.
  
  
  METHODS
  The study population consisted of 186 consecutive prostate cancer patients treated with an image-guided radiotherapy (IGRT) hypofractionated protocol using 3 techniques: 32 with X-ray, 30 with CBCT, and 124 with US. Treatment dose of 70.2 Gy was delivered in 26 fractions with a conformal dynamic arcs technique. Interfraction prostate localization errors were determined for the 3 techniques. Moreover, interfraction and intrafraction prostate motion in terms of translations and rotations, as well as residual errors, were determined with X-ray.
  
  
  RESULTS
  The systematic and random components of the prostate localization errors were as follows: (1) with X-ray 3.0 ± 3.4, 2.3 ± 2.7, 1.8 ± 2.3 mm in anterior-posterior (AP), superior-inferior (SI), and left-right (LR) directions and 1.8° ± 1.2°, 2.3° ± 1.5°, 2.7° ± 3.1°, for the yaw, roll, and pitch rotations; (2) with CBCT 3.5 ± 4.2, 3.3 ± 3.3, 2.5 ± 3.1 mm in AP, SI, and LR directions; (3) with US 3.7 ± 4.7, 3.4 ± 4.3, 2.3 ± 3.5 mm in AP, SI, and LR directions. Residual errors with X-ray were less than 1 mm in all directions. Intrafraction prostate motion of less than 0.5 mm in LR and of the order of 1 mm in AP and SI directions was found. This led to a significant reduction of the margins, potentially important for dose escalation studies.
  
  
  CONCLUSIONS
  Daily on-line IGRT with stereoscopic X-ray imaging allowed a consistent PTV margin reduction considering residual interfraction prostate localization error and intrafraction motion. X-ray offers the best compromise among accuracy, reliability, dose to the patient, and time investment for daily IGRT treatment of prostate.
authors.affiliation: 1 Medical Physics Unit, European Institute of Oncology, Milan - Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Garibaldi
authors.forename: Barbara Alicja
authors.initials: BA
authors.lastname: Jereczek-Fossa
authors.forename: Dario
authors.initials: D
authors.lastname: Zerini
authors.forename: Raffaella
authors.initials: R
authors.lastname: Cambria
authors.forename: Annamaria
authors.initials: A
authors.lastname: Ferrari
authors.forename: Flavia
authors.initials: F
authors.lastname: Serafini
authors.forename: Federica
authors.initials: F
authors.lastname: Cattani
authors.forename: Barbara
authors.initials: B
authors.lastname: Tagaste
authors.forename: Cristiana
authors.initials: C
authors.lastname: Fodor
authors.forename: Rosa
authors.initials: R
authors.lastname: Luraschi
authors.forename: Roberto
authors.initials: R
authors.lastname: Orecchia
mesh_terms: D000368:Aged; D054893:Cone-Beam Computed Tomography; D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D016896:Treatment Outcome; D018084:Ultrasonography, Interventional