title: Dosimetric effect of CT contrast agent in CyberKnife treatment plans.
abstract: BACKGROUND
  To investigate the effect of computed tomography (CT) contrast enhancement (CE) on the 3D dose distributions of non-coplanar small field beams in the CyberKnife (CK) treatment planning system (TPS) for the stereotactic ablative radiotherapy (SABR).
  
  
  METHODS
  Twenty-two pre-CE CT treatment plans were recruited to this retrospective plan study. Their post-CE CT plans were based on the pre-CE CT plan data and calculated using the same MU and beam paths in either Ray-Tracing or Monte Carlo (MC) algorithms. The differences in the doses of the beam path and the reference point between the pre- and post-CE CT plans were compared. The minimum, maximum, and mean doses in dose-volume histograms (DVHs) of target and organs-at-risk (OARs) were also compared.
  
  
  RESULTS
  The dose differences between the pre- and post-CE plans in a single beam path were less than 1.05% in both calculation algorithms, with respect to the prescription dose. At the center of the target volume, it was 1.9% (maximum 6.2%) in Ray-Tracing and 1.6% (maximum 4.0%) in MC. The CA effect showed on average 1.2% difference in the OAR maximum dose (maximum 7.8% in Ray-Tracing and 7.2% in MC). In the lung cases, the CT CE resulted in a dose difference of 2.4% (from 1.0% to 6.5%) without the calculation algorithm effect (maximum 20.3%).
  
  
  CONCLUSIONS
  The CK treatment plan using the post-CE CT generally afforded less than 2% dose differences from the pre-CE CT plan. However, it could be up to 7.8% depending on the target positions in a body and be more than 20% with the calculation algorithms. Thus, the post-CE CT in CK treatment plans should be used with careful consideration for the CA effect, target position, and calculation algorithm factors.
authors.forename: Hee Jung
authors.initials: HJ
authors.lastname: Kim
authors.forename: Ah Ram
authors.initials: AR
authors.lastname: Chang
authors.forename: Yang-Kyun
authors.initials: YK
authors.lastname: Park
authors.affiliation: Department of Radiation Oncology, Seoul National University Hospital, Seoul, South Korea. sye@snu.ac.kr.
authors.forename: Sung-Joon
authors.initials: SJ
authors.lastname: Ye
mesh_terms: D003287:Contrast Media / Q000494:pharmacology*; D006801:Humans; D009369:Neoplasms / Q000601:surgery*; D058958:Organs at Risk; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed
chemical_list: D003287:Contrast Media