title: Impact of target point deviations on control and complication probabilities in stereotactic radiosurgery of AVMs and metastases.
abstract: OBJECTIVE
  Determination of the impact of inaccuracies in the determination and setup of the target point in stereotactic radiosurgery (SRS) on the expectable complication and control probabilities.
  
  
  METHODS
  Two randomized samples of patients with arteriovenous malformation (AVM) (n=20) and with brain metastases (n=20) treated with SRS were formed, and the probability for complete obliteration (COP) or complete remission (CRP), the size of the 10 Gy-volume in the brain tissue (VOI10), and the probability for radiation necrosis (NTCP) were calculated. The dose-effect relations for COP and CRP were fitted to clinical data. Target point deviations were simulated through random vectors and the resulting probabilities and volumes were calculated and compared with the values of the treatment plan.
  
  
  RESULTS
  The decrease of the relative value of the control probabilities at 1mm target point deviation was up to 4% for AVMs and up to 10% for metastases. At 2 mm the median decrease was 5% for AVMs and 9% for metastases. The value for the target point deviation, at which COP and CRP decreased about 0.05 in 90% of the cases, was 1.3 mm. The increase of NTCP was maximally 0.0025 per mm target point deviation for AVMs and 0.0035/mm for metastases. The maximal increase of VOI10 was 0.7 cm(3)/mm target point deviation in both patient groups.
  
  
  CONCLUSIONS
  The upper limit for tolerable target point deviations is at 1.3mm. If this value cannot be achieved during the system test, a supplementary safety margin should be applied for the definition of the target volume. A better accuracy level is desirable, in order to ensure optimal chances for the success of the treatment. The target point precision is less important for the minimization of the probability of radiation necroses.
authors.affiliation: Department of Stereotaxy and Functional Neurosurgery, University of Cologne, Germany. harald.treuer@uk-koeln.de
authors.forename: Harald
authors.initials: H
authors.lastname: Treuer
authors.forename: Martin
authors.initials: M
authors.lastname: Kocher
authors.forename: Moritz
authors.initials: M
authors.lastname: Hoevels
authors.forename: Stefan
authors.initials: S
authors.lastname: Hunsche
authors.forename: Klaus
authors.initials: K
authors.lastname: Luyken
authors.forename: Mohammad
authors.initials: M
authors.lastname: Maarouf
authors.forename: Jürgen
authors.initials: J
authors.lastname: Voges
authors.forename: Rolf-Peter
authors.initials: RP
authors.lastname: Müller
authors.forename: Volker
authors.initials: V
authors.lastname: Sturm
mesh_terms: D001921:Brain / Q000473:pathology; D001932:Brain Neoplasms / Q000556:secondary / Q000601:surgery*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000601:surgery*; D019300:Medical Errors / Q000009:adverse effects*; D009336:Necrosis / Q000209:etiology; D011336:Probability; D016634:Radiosurgery / Q000009:adverse effects*; D012074:Remission Induction; D012189:Retrospective Studies; D016896:Treatment Outcome