title: Prostate stereotactic ablative radiation therapy using volumetric modulated arc therapy to dominant intraprostatic lesions.
abstract: OBJECTIVE
  To investigate boosting dominant intraprostatic lesions (DILs) in the context of stereotactic ablative radiation therapy (SABR) and to examine the impact on tumor control probability (TCP) and normal tissue complication probability (NTCP).
  
  
  METHODS
  Ten prostate datasets were selected. DILs were defined using T2-weighted, dynamic contrast-enhanced and diffusion-weighted magnetic resonance imaging. Four plans were produced for each dataset: (1) no boost to DILs; (2) boost to DILs, no seminal vesicles in prescription; (3) boost to DILs, proximal seminal vesicles (proxSV) prescribed intermediate dose; and (4) boost to DILs, proxSV prescribed higher dose. The prostate planning target volume (PTV) prescription was 42.7 Gy in 7 fractions. DILs were initially prescribed 115% of the PTV(Prostate) prescription, and PTV(DIL) prescriptions were increased in 5% increments until organ-at-risk constraints were reached. TCP and NTCP calculations used the LQ-Poisson Marsden, and Lyman-Kutcher-Burman models respectively.
  
  
  RESULTS
  When treating the prostate alone, the median PTV(DIL) prescription was 125% (range: 110%-140%) of the PTV(Prostate) prescription. Median PTV(DIL) D50% was 55.1 Gy (range: 49.6-62.6 Gy). The same PTV(DIL) prescriptions and similar PTV(DIL) median doses were possible when including the proxSV within the prescription. TCP depended on prostate α/β ratio and was highest with an α/β ratio = 1.5 Gy, where the additional TCP benefit of DIL boosting was least. Rectal NTCP increased with DIL boosting and was considered unacceptably high in 5 cases, which, when replanned with an emphasis on reducing maximum dose to 0.5 cm(3) of rectum (Dmax(0.5cc)), as well as meeting existing constraints, resulted in considerable rectal NTCP reductions.
  
  
  CONCLUSIONS
  Boosting DILs in the context of SABR is technically feasible but should be approached with caution. If this therapy is adopted, strict rectal constraints are required including Dmax(0.5cc). If the α/β ratio of prostate cancer is 1.5 Gy or less, then high TCP and low NTCP can be achieved by prescribing SABR to the whole prostate, without the need for DIL boosting.
authors.affiliation: Department of Clinical Oncology, Leeds Cancer Centre, St. James's University Hospital, Leeds, United Kingdom; University of Leeds, Leeds, United Kingdom.
authors.forename: Louise J
authors.initials: LJ
authors.lastname: Murray
authors.affiliation: Department of Medical Physics, Leeds Cancer Centre, St. James's University Hospital, Leeds, United Kingdom.
authors.forename: John
authors.initials: J
authors.lastname: Lilley
authors.affiliation: Department of Medical Physics, Leeds Cancer Centre, St. James's University Hospital, Leeds, United Kingdom.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Thompson
authors.affiliation: Department of Medical Physics, Leeds Cancer Centre, St. James's University Hospital, Leeds, United Kingdom.
authors.forename: Vivian
authors.initials: V
authors.lastname: Cosgrove
authors.affiliation: Department of Medical Physics, Leeds Cancer Centre, St. James's University Hospital, Leeds, United Kingdom; University of Leeds, Leeds, United Kingdom.
authors.forename: Josh
authors.initials: J
authors.lastname: Mason
authors.affiliation: Department of Medical Physics, Leeds Cancer Centre, St. James's University Hospital, Leeds, United Kingdom.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Sykes
authors.affiliation: Department of Clinical Oncology, Leeds Cancer Centre, St. James's University Hospital, Leeds, United Kingdom.
authors.forename: Kevin
authors.initials: K
authors.lastname: Franks
authors.affiliation: Department of Clinical Oncology, Leeds Cancer Centre, St. James's University Hospital, Leeds, United Kingdom; University of Leeds, Leeds, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Sebag-Montefiore
authors.affiliation: Department of Clinical Oncology, Leeds Cancer Centre, St. James's University Hospital, Leeds, United Kingdom. Electronic address: Ann.Henry@leedsth.nhs.uk.
authors.forename: Ann M
authors.initials: AM
authors.lastname: Henry
mesh_terms: D003287:Contrast Media; D019583:Dose Fractionation, Radiation; D005240:Feasibility Studies; D005270:Femur Head / Q000000981:diagnostic imaging / Q000528:radiation effects; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects*; D011336:Probability; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000517:prevention & control*; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects*; D012669:Seminal Vesicles / Q000000981:diagnostic imaging / Q000528:radiation effects; D047368:Tumor Burden; D014521:Urethra / Q000000981:diagnostic imaging / Q000528:radiation effects; D001743:Urinary Bladder / Q000000981:diagnostic imaging / Q000528:radiation effects
chemical_list: D003287:Contrast Media