title: Optimal source distribution for focal boosts using high dose rate (HDR) brachytherapy alone in prostate cancer.
abstract: OBJECTIVE
  To investigate the optimal distribution of sources using high dose rate brachytherapy to deliver a focal boost to a dominant lesion within the whole prostate gland based on multi-parametric magnetic resonance imaging (mpMRI).
  
  
  METHODS
  Sixteen patients with prostate cancer underwent mpMRI each of which demonstrated a dominant lesion. There were single lesions in 6 patients, two lesions in 4 and 3 lesions in 6 patients. Two dosimetric models and parameters were compared in each case. The first model used 10mm intervals between needles, and the second model used additional needles at 5 mm intervals between each needle in the boost area.
  
  
  RESULTS
  Three of thirty-two plans did not achieve the plan objectives. These three plans were in the first model. A higher median urethral volume was seen in the 'unsuccessful' group (2.7 cc, and 1.9 cc, respectively, p-value=0.12). Conformity indices of the second model were also better than the first model (COIN index; 0.716 and 0.643, respectively).
  
  
  CONCLUSIONS
  Focal monotherapy based on mpMRI achieves optimal dosimetry by individualizing the needle positions using 5mm spacing rather than 10mm spacing within the boost volume. A larger urethral volume may have an adverse effect on this distribution. Formal clinical evaluation of this approach is currently underway.
authors.affiliation: Mount Vernon Cancer Centre, Northwood, United Kingdom; Division of Radiation Oncology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand. Electronic address: pittaya.dan@mahidol.ac.th.
authors.forename: Pittaya
authors.initials: P
authors.lastname: Dankulchai
authors.affiliation: Mount Vernon Cancer Centre, Northwood, United Kingdom.
authors.forename: Roberto
authors.initials: R
authors.lastname: Alonzi
authors.affiliation: Mount Vernon Cancer Centre, Northwood, United Kingdom.
authors.forename: Gerry J
authors.initials: GJ
authors.lastname: Lowe
authors.affiliation: Mount Vernon Cancer Centre, Northwood, United Kingdom.
authors.forename: James
authors.initials: J
authors.lastname: Burnley
authors.affiliation: Paul Strickland Scanner Centre, Mount Vernon Cancer Centre, Northwood, United Kingdom.
authors.forename: Anwar R
authors.initials: AR
authors.lastname: Padhani
authors.affiliation: Mount Vernon Cancer Centre, Northwood, United Kingdom.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Hoskin
mesh_terms: D000368:Aged; D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009339:Needles; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011874:Radiometry; D011879:Radiotherapy Dosage; D014521:Urethra / Q000528:radiation effects
keywords: Dominant lesion; Focal monotherapy; HDR brachytherapy; Multi-parametric MRI; Prostate cancer