title: Direction-modulated brachytherapy for high-dose-rate treatment of cervical cancer. I: theoretical design.
abstract: OBJECTIVE
  To demonstrate that utilization of the direction-modulated brachytherapy (DMBT) concept can significantly improve treatment plan quality in the setting of high-dose-rate (HDR) brachytherapy for cervical cancer.
  
  
  METHODS
  The new, MRI-compatible, tandem design has 6 peripheral holes of 1.3-mm diameter, grooved along a nonmagnetic tungsten-alloy rod (ρ = 18.0 g/cm(3)), enclosed in Delrin tubing (polyoxymethylene, ρ = 1.41 g/cm(3)), with a total thickness of 6.4 mm. The Monte Carlo N-Particle code was used to calculate the anisotropic (192)Ir dose distributions. An in-house-developed inverse planning platform, geared with simulated annealing and constrained-gradient optimization algorithms, was used to replan 15 patient cases (total 75 plans) treated with a conventional tandem and ovoids (T&O) applicator. Prescription dose was 6 Gy. For replanning, we replaced the conventional tandem with that of the new DMBT tandem for optimization but left the ovoids in place and kept the dwell positions as originally planned. All DMBT plans were normalized to match the high-risk clinical target volume V100 coverage of the T&O plans.
  
  
  RESULTS
  In general there were marked improvements in plan quality for the DMBT plans. On average, D2cc for the bladder, rectum, and sigmoid were reduced by 0.59 ± 0.87 Gy (8.5% ± 28.7%), 0.48 ± 0.55 Gy (21.1% ± 27.2%), and 0.10 ± 0.38 Gy (40.6% ± 214.9%) among the 75 plans, with best single-plan reductions of 3.20 Gy (40.8%), 2.38 Gy (40.07%), and 1.26 Gy (27.5%), respectively. The high-risk clinical target volume D90 was similar, with 6.55 ± 0.96 Gy and 6.59 ± 1.06 Gy for T&O and DMBT, respectively.
  
  
  CONCLUSIONS
  Application of the DMBT concept to cervical cancer allowed for improved organ at risk sparing while achieving similar target coverage on a sizeable patient population, as intended, by maximally utilizing the anatomic information contained in 3-dimensional imaging. A series of mechanical and clinical validations are to be followed.
authors.affiliation: Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California; Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, California.
authors.forename: Dae Yup
authors.initials: DY
authors.lastname: Han
authors.affiliation: Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California; Department of Physics, University of California San Diego, La Jolla, California.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Webster
authors.affiliation: Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Scanderbeg
authors.affiliation: Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California.
authors.forename: Catheryn
authors.initials: C
authors.lastname: Yashar
authors.affiliation: Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California.
authors.forename: Dongju
authors.initials: D
authors.lastname: Choi
authors.affiliation: Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California.
authors.forename: Bongyong
authors.initials: B
authors.lastname: Song
authors.affiliation: Medical Physics Unit, McGill University, Montréal, Québec, Canada; Department of Radiation Oncology, Jewish General Hospital, Montréal, Québec, Canada.
authors.forename: Slobodan
authors.initials: S
authors.lastname: Devic
authors.affiliation: Department of Medical Physics, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Ananth
authors.initials: A
authors.lastname: Ravi
authors.affiliation: Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California; Department of Medical Physics, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada. Electronic address: wyjsong@gmail.com.
authors.forename: William Y
authors.initials: WY
authors.lastname: Song
mesh_terms: D000328:Adult; D000465:Algorithms; D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D012809:Colon, Sigmoid / Q000528:radiation effects; D004867:Equipment Design; D005260:Female; D006801:Humans; D007496:Iridium Radioisotopes / Q000627:therapeutic use; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009010:Monte Carlo Method; D058958:Organs at Risk / Q000528:radiation effects*; D011832:Radiation Injuries / Q000517:prevention & control*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012007:Rectum / Q000528:radiation effects; D014414:Tungsten; D001743:Urinary Bladder / Q000528:radiation effects; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*; D055815:Young Adult
chemical_list: D007496:Iridium Radioisotopes; D014414:Tungsten