title: Intra-operative 3D guidance and edema detection in prostate brachytherapy using a non-isocentric C-arm.
abstract: OBJECTIVE
  Brachytherapy (radioactive seed insertion) has emerged as one of the most effective treatment options for patients with prostate cancer, with the added benefit of a convenient outpatient procedure. The main limitation in contemporary brachytherapy is faulty seed placement, predominantly due to the presence of intra-operative edema (tissue expansion). Though currently not available, the capability to intra-operatively monitor the seed distribution, can make a significant improvement in cancer control. We present such a system here.
  
  
  METHODS
  Intra-operative measurement of edema in prostate brachytherapy requires localization of inserted radioactive seeds relative to the prostate. Seeds were reconstructed using a typical non-isocentric C-arm, and exported to a commercial brachytherapy treatment planning system. Technical obstacles for 3D reconstruction on a non-isocentric C-arm include pose-dependent C-arm calibration; distortion correction; pose estimation of C-arm images; seed reconstruction; and C-arm to TRUS registration.
  
  
  RESULTS
  In precision-machined hard phantoms with 40-100 seeds and soft tissue phantoms with 45-87 seeds, we correctly reconstructed the seed implant shape with an average 3D precision of 0.35 mm and 0.24 mm, respectively. In a DoD Phase-1 clinical trial on six patients with 48-82 planned seeds, we achieved intra-operative monitoring of seed distribution and dosimetry, correcting for dose inhomogeneities by inserting an average of over four additional seeds in the six enrolled patients (minimum 1; maximum 9). Additionally, in each patient, the system automatically detected intra-operative seed migration induced due to edema (mean 3.84 mm, STD 2.13 mm, Max 16.19 mm).
  
  
  CONCLUSIONS
  The proposed system is the first of a kind that makes intra-operative detection of edema (and subsequent re-optimization) possible on any typical non-isocentric C-arm, at negligible additional cost to the existing clinical installation. It achieves a significantly more homogeneous seed distribution, and has the potential to affect a paradigm shift in clinical practice. Large scale studies and commercialization are currently underway.
authors.affiliation: Johns Hopkins University, Baltimore, MD 21210, United States. Ameet.Jain@Philips.com
authors.forename: A
authors.initials: A
authors.lastname: Jain
authors.forename: A
authors.initials: A
authors.lastname: Deguet
authors.forename: I
authors.initials: I
authors.lastname: Iordachita
authors.forename: G
authors.initials: G
authors.lastname: Chintalapani
authors.forename: S
authors.initials: S
authors.lastname: Vikal
authors.forename: J
authors.initials: J
authors.lastname: Blevins
authors.forename: Y
authors.initials: Y
authors.lastname: Le
authors.forename: E
authors.initials: E
authors.lastname: Armour
authors.forename: C
authors.initials: C
authors.lastname: Burdette
authors.forename: D
authors.initials: D
authors.lastname: Song
authors.forename: G
authors.initials: G
authors.lastname: Fichtinger
mesh_terms: D001918:Brachytherapy / Q000009:adverse effects*; D004487:Edema / Q000000981:diagnostic imaging* / Q000209:etiology* / Q000517:prevention & control; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D011300:Preoperative Care / Q000379:methods; D011471:Prostatic Neoplasms / Q000150:complications / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D011881:Radiotherapy, Computer-Assisted / Q000379:methods; D014463:Ultrasonography / Q000379:methods*