title: Evaluation of the setup margins for cone beam computed tomography-guided cranial radiosurgery: A phantom study.
abstract: The aim of this study is to evaluate the setup margins from the clinical target volume (CTV) to planning target volume (PTV) for cranial stereotactic radiosurgery (SRS) treatments guided by cone beam computed tomography (CBCT). We designed an end-to-end (E2E) test using a skull phantom with an embedded 6mm tungsten ball (target). A noncoplanar plan was computed (E2E plan) to irradiate the target. The CBCT-guided positioning of the skull phantom on the linac was performed. Megavoltage portal images were acquired after 15 independent deliveries of the E2E plan. The displacement 2-dimensional (2D) vector between the centers of the square field and the ball target on each portal image was used to quantify the isocenter accuracy. Geometrical margins on each patient׳s direction (left-right or LR, anterior-posterior or AP, superior-inferior or SI) were calculated. Dosimetric validation of the margins was performed in 5 real SRS cases: 3-dimesional (3D) isocenter deviations were mimicked, and changes in CTV dose coverage and organs-at-risk (OARs) dosage were analyzed. The CTV-PTV margins of 1.1mm in LR direction, and 0.7mm in AP and SI directions were derived from the E2E tests. The dosimetric analysis revealed that a 1-mm uniform margin was sufficient to ensure the CTV dose coverage, without compromising the OAR dose tolerances. The effect of isocenter uncertainty has been estimated to be 1mm in our CBCT-guided SRS approach.
authors.affiliation: Department of Radiation Oncology, Hospital Quirón, Barcelona, Spain. Electronic address: jfcdrr@yahoo.es.
authors.forename: Juan Francisco
authors.initials: JF
authors.lastname: Calvo Ortega
authors.affiliation: Department of Radiotherapy, Erasmus MC Cancer Institute, University Medical Center Rotterdam, Rotterdam, The Netherlands.
authors.forename: Wouter
authors.initials: W
authors.lastname: Wunderink
authors.affiliation: Department of Radiation Oncology, Hospital Quirón, Barcelona, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Delgado
authors.affiliation: Department of Radiation Oncology, Hospital Quirón, Barcelona, Spain.
authors.forename: Sandra
authors.initials: S
authors.lastname: Moragues
authors.affiliation: Department of Radiation Oncology, Hospital Quirón, Barcelona, Spain.
authors.forename: Miquel
authors.initials: M
authors.lastname: Pozo
authors.affiliation: Department of Radiation Oncology, Hospital Quirón, Barcelona, Spain.
authors.forename: Joan
authors.initials: J
authors.lastname: Casals
mesh_terms: D001932:Brain Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D058958:Organs at Risk; D019047:Phantoms, Imaging; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000009:adverse effects / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000009:adverse effects / Q000379:methods*; D047368:Tumor Burden
keywords: CBCT; CTV; Isocenter; Margin; SRS