title: Neurovascular bundle-sparing radiotherapy for prostate cancer using MRI-CT registration: A dosimetric feasibility study.
abstract: OBJECTIVE
  Sexual dysfunction after radiotherapy for prostate cancer remains an important late adverse toxicity. The neurovascular bundles (NVB) that lie posterolaterally to the prostate are typically spared during prostatectomy, but in traditional radiotherapy planning they are not contoured as an organ-at-risk with dose constraints. Our goal was to determine the dosimetric feasibility of "NVB-sparing" prostate radiotherapy while still delivering adequate dose to the prostate.
  
  
  METHODS
  Twenty-five consecutive patients with prostate cancer (with no extraprostatic disease on pelvic magnetic resonance imaging [MRI]) who that were treated with external beam radiotherapy, with the same primary planning target volume margins, to a dose of 79.2 Gy were evaluated. Pelvic MRI and simulation computed tomography scans were registered using dedicated software to allow for bilateral NVB target delineation on T2-weighted MRI. A volumetric modulated arc therapy plan was generated using the NVB bilaterally with 2 mm margin as an organ to spare and compared to the patient's previously delivered plan. Dose-volume histogram endpoints for NVB, rectum, bladder, and planning target volume 79.2 were compared between the 2 plans using a 2-tailed paired t-test.
  
  
  RESULTS
  The V70 for the NVB was significantly lower on the NVB-sparing plan (p <0.01), while rectum and bladder endpoints were similar. Target V100% was similar but V105%was higher for the NVB-sparing plans (p <0.01).
  
  
  CONCLUSIONS
  "NVB-sparing" radiotherapy is dosimetrically feasible using CT-MRI registration, and for volumetric modulated arc therapy technology - target coverage is acceptable without increased dose to other normal structures, but with higher target dose inhomogeneity. The clinical impact of "NVB-sparing" radiotherapy is currently under study at our institution.
authors.affiliation: Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, GA. Electronic address: richardjcassidy@emory.edu.
authors.forename: R J
authors.initials: RJ
authors.lastname: Cassidy
authors.affiliation: Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, GA.
authors.forename: X
authors.initials: X
authors.lastname: Yang
authors.affiliation: Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, GA.
authors.forename: T
authors.initials: T
authors.lastname: Liu
authors.affiliation: Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, GA.
authors.forename: M
authors.initials: M
authors.lastname: Thomas
authors.affiliation: Department of Radiology, Emory University, Atlanta, GA.
authors.forename: S G
authors.initials: SG
authors.lastname: Nour
authors.affiliation: Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, GA.
authors.forename: A B
authors.initials: AB
authors.lastname: Jani
mesh_terms: D000368:Aged; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden
keywords: MRI-CT registration; Neurovascular bundle sparing; VMAT