title: Treatment Planning Considerations for Robotic Guided Cardiac Radiosurgery for Atrial Fibrillation.
abstract: OBJECTIVE
  Robotic guided stereotactic radiosurgery has recently been investigated for the treatment of atrial fibrillation (AF). Before moving into human treatments, multiple implications for treatment planning given a potential target tracking approach have to be considered.
  
  
  METHODS
  Theoretical AF radiosurgery treatment plans for twenty-four patients were generated for baseline comparison. Eighteen patients were investigated under ideal tracking conditions, twelve patients under regional dose rate (RDR = applied dose over a certain time window) optimized conditions (beam delivery sequence sorting according to regional beam targeting), four patients under ultrasound tracking conditions (beam block of the ultrasound probe) and four patients with temporary single fiducial tracking conditions (differential surrogate-to-target respiratory and cardiac motion).
  
  
  RESULTS
  With currently known guidelines on dose limitations of critical structures, treatment planning for AF radiosurgery with 25 Gy under ideal tracking conditions with a 3 mm safety margin may only be feasible in less than 40% of the patients due to the unfavorable esophagus and bronchial tree location relative to the left atrial antrum (target area). Beam delivery sequence sorting showed a large increase in RDR coverage (% of voxels having a larger dose rate for a given time window) of 10.8-92.4% (median, 38.0%) for a 40-50 min time window, which may be significant for non-malignant targets. For ultrasound tracking, blocking beams through the ultrasound probe was found to have no visible impact on plan quality given previous optimal ultrasound window estimation for the planning CT. For fiducial tracking in the right atrial septum, the differential motion may reduce target coverage by up to -24.9% which could be reduced to a median of -0.8% (maximum, -12.0%) by using 4D dose optimization. The cardiac motion was also found to have an impact on the dose distribution, at the anterior left atrial wall; however, the results need to be verified.
  
  
  CONCLUSIONS
  Robotic AF radiosurgery with 25 Gy may be feasible in a subgroup of patients under ideal tracking conditions. Ultrasound tracking was found to have the lowest impact on treatment planning and given its real-time imaging capability should be considered for AF robotic radiosurgery. Nevertheless, advanced treatment planning using RDR or 4D respiratory and cardiac dose optimization may be still advised despite using ideal tracking methods.
authors: Department for Radiation Oncology, University Medical Center Schleswig-Holstein, Campus Kiel, Germany ; Saphir Radiosurgery Center, Frankfurt and Güstrow, Germany.
authors: Oliver
authors: O
authors: Blanck
authors: Robotics and Cognitive Systems, University of Lübeck.
authors: Svenja
authors: S
authors: Ipsen
authors: Department for Radiation Oncology, University Medical Center Schleswig-Holstein, Campus Kiel, Germany ; Department for Radiation Oncology, Tuen Mun Hospital, Hong Kong, Hong Kong.
authors: Mark K
authors: MK
authors: Chan
authors: Institute for Diagnostics and Interventional Radiology, University Clinic Frankfurt, Germany ; Department for Radiology and Nuclear Medicine, Kantonsspital St. Gallen, Switzerland.
authors: Ralf
authors: R
authors: Bauer
authors: Institute for Diagnostics and Interventional Radiology, University Clinic Frankfurt, Germany ; Radiology, Darmstadt, Germany.
authors: Matthias
authors: M
authors: Kerl
authors: Clinic for Radiology and Nuclear Medicine, University Medical Center Schleswig-Holstein, Campus Lübeck, Germany.
authors: Peter
authors: P
authors: Hunold
authors: Institute for Diagnostics and Interventional Radiology, University Clinic Frankfurt, Germany.
authors: Volkmar
authors: V
authors: Jacobi
authors: Institute for Robotics and Cognitive Systems, University of Lubeck.
authors: Ralf
authors: R
authors: Bruder
authors: Institute for Robotics and Cognitive Systems, University of Luebeck, Institute for Robotics and Cognitive Systems, University of Lubeck.
authors: Achim
authors: A
authors: Schweikard
authors: Department for Radiation Oncology, University Medical Center Schleswig-Holstein, Campus Lübeck, Germany.
authors: Dirk
authors: D
authors: Rades
authors: Institute for Diagnostics and Interventional Radiology, University Clinic Frankfurt, Germany.
authors: Thomas J
authors: TJ
authors: Vogl
authors: Department for Thoracic, Cardiac and Thoracic Vascular Surgery, University Clinic Frankfurt, Germany.
authors: Peter
authors: P
authors: Kleine
authors: Cardiology Department, Sana Clinic Oldenburg in Holstein.
authors: Frank
authors: F
authors: Bode
authors: Department for Radiation Oncology, University Medical Center Schleswig-Holstein, Campus Kiel, Germany ; Department for Radiation Oncology, University Medical Center Copenhagen, Denmark.
authors: Jürgen
authors: J
authors: Dunst
keywords: 4d dose calculation; atrial fibrillation; cyberknife cardiac radiosurgery; dose rate optimization; pulmonary vein isolation; stereotactic body radiation therapy; treatment planning