title: Adequacy of inhale/exhale breathhold CT based ITV margins and image-guided registration for free-breathing pancreas and liver SBRT.
abstract: OBJECTIVE
  To evaluate use of breath-hold CTs and implanted fiducials for definition of the internal target volume (ITV) margin for upper abdominal stereotactic body radiation therapy (SBRT). To study the statistics of inter- and intra-fractional motion information.
  
  
  METHODS
  11 patients treated with SBRT for locally advanced pancreatic cancer (LAPC) or liver cancer were included in the study. Patients underwent fiducial implantation, free-breathing CT and breath-hold CTs at end inhalation/exhalation. All patients were planned and treated with SBRT using volumetric modulated arc therapy (VMAT). Two margin strategies were studied: Strategy I uses PTV = ITV + 3 mm; Strategy II uses PTV = GTV + 1.5 cm. Both CBCT and kV orthogonal images were taken and analyzed for setup before patient treatments. Tumor motion statistics based on skeletal registration and on fiducial registration were analyzed by fitting to Gaussian functions.
  
  
  RESULTS
  All 11 patients met SBRT planning dose constraints using strategy I. Average ITV margins for the 11 patients were 2 mm RL, 6 mm AP, and 6 mm SI. Skeletal registration resulted in high probability (RL = 69%, AP = 4.6%, SI = 39%) that part of the tumor will be outside the ITV. With the 3 mm ITV expansion (Strategy 1), the probability reduced to RL 32%, AP 0.3%, SI 20% for skeletal registration; and RL 1.2%, AP 0%, SI 7% for fiducial registration. All 7 pancreatic patients and 2 liver patients failed to meet SBRT dose constraints using strategy II. The liver dose was increased by 36% for the other 2 liver patients that met the SBRT dose constraints with strategy II.
  
  
  CONCLUSIONS
  Image guidance matching to skeletal anatomy is inadequate for SBRT positioning in the upper abdomen and usage of fiducials is highly recommended. Even with fiducial implantation and definition of an ITV, a minimal 3 mm planning margin around the ITV is needed to accommodate intra-fractional uncertainties.
authors.affiliation: Department of Radiation Oncology, Cedars Sinai Medical Center, Los Angeles, CA 90048, USA. Wensha.Yang@cshs.org.
authors.forename: Wensha
authors.initials: W
authors.lastname: Yang
authors.forename: Benedick A
authors.initials: BA
authors.lastname: Fraass
authors.forename: Robert
authors.initials: R
authors.lastname: Reznik
authors.forename: Nicholas
authors.initials: N
authors.lastname: Nissen
authors.forename: Simon
authors.initials: S
authors.lastname: Lo
authors.forename: Laith H
authors.initials: LH
authors.lastname: Jamil
authors.forename: Kapil
authors.initials: K
authors.lastname: Gupta
authors.forename: Howard
authors.initials: H
authors.lastname: Sandler
authors.forename: Richard
authors.initials: R
authors.lastname: Tuli
mesh_terms: D062485:Breath Holding; D015331:Cohort Studies; D045853:Exhalation / Q000502:physiology; D057918:Fiducial Markers; D006801:Humans; D001239:Inhalation / Q000502:physiology; D008113:Liver Neoplasms / Q000601:surgery*; D009038:Motion; D010190:Pancreatic Neoplasms / Q000601:surgery*; D016634:Radiosurgery / Q000009:adverse effects / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000009:adverse effects / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects / Q000379:methods; D012119:Respiration; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden; D018084:Ultrasonography, Interventional