title: Effect of androgen deprivation therapy on intraprostatic tumour volume identified on18F choline PET/CT for prostate dose painting radiotherapy.
abstract: OBJECTIVE
  Prostate dose painting radiotherapy requires the accurate identification of dominant intraprostatic lesions (DILs) to be used as boost volumes; these can be identified on multiparametric MRI (mpMRI) or choline positron emission tomography (PET)/CT. Planning scans are usually performed after 2-3 months of androgen deprivation therapy (ADT). We examine the effect of ADT on choline tracer uptake and boost volumes identified on choline PET/CT.
  
  
  METHODS
  Fluoroethylcholine (18F choline) PET/CT was performed for dose painting radiotherapy planning in patients with intermediate- to high-risk prostate cancer. Initially, they were performed at planning. Owing to low visual tracer uptake, PET/CT for subsequent patients was performed at staging. We compared these two approaches on intraprostatic lesions obtained on PET using both visual and automatic threshold methods [prostate maximum standardized uptake value (SUVmax) 60%] when compared with mpMRI.
  
  
  RESULTS
  PET/CT was performed during ADT in 11 patients (median duration of 85 days) and before ADT in 29 patients. ADT significantly reduced overall prostate volume by 17%. During ADT, prostate SUVmaxwas lower although it did not reach statistical significance (4.2 vs 6.6, p = 0.06); three patients had no visually identifiable PET DIL; and visually defined PET DILs were significantly smaller than corresponding mpMRI DILs (p = 0.03). However, all patients scanned before ADT had at least one visually identifiable PET DIL, with no significant size difference between MRI and visually defined PET DILs. In both groups, threshold PET produced larger DILs than visual PET. Both PET methods have moderate sensitivity (0.50-0.68) and high specificity (0.85-0.98) for identifying MRI-defined disease.
  
  
  CONCLUSIONS
  For visual contouring of boost volumes in prostate dose painting radiotherapy,18F choline PET/CT should be performed before ADT. For threshold contouring of boost volumes using our PET/CT scanning protocol, threshold levels of above 60% prostate SUVmaxmay be more suitable. Additional use of PET with MRI for radiotherapy planning can significantly change the overall boost volumes compared with using MRI alone. Advances in knowledge: For prostate dose painting radiotherapy, the additional use of18F choline PET with MRI can significantly change the overall boost volumes, and PET should be performed before hormone therapy, especially if boost volumes are visually identified.
authors.affiliation: 1 Radiotherapy Department, Clatterbridge Cancer Centre NHS Foundation Trust, Bebington, UK.
authors.forename: Joachim
authors.identifier: http://orcid.org/0000-0001-8465-5159
authors.initials: J
authors.lastname: Chan
authors.affiliation: 1 Radiotherapy Department, Clatterbridge Cancer Centre NHS Foundation Trust, Bebington, UK.
authors.forename: Antony
authors.initials: A
authors.lastname: Carver
authors.affiliation: 1 Radiotherapy Department, Clatterbridge Cancer Centre NHS Foundation Trust, Bebington, UK.
authors.forename: John N H
authors.initials: JN
authors.lastname: Brunt
authors.affiliation: 2 Nuclear Medicine Department, Royal Liverpool and Broadgreen University Hospitals NHS Trust, Liverpool, UK.
authors.forename: Sobhan
authors.initials: S
authors.lastname: Vinjamuri
authors.affiliation: 1 Radiotherapy Department, Clatterbridge Cancer Centre NHS Foundation Trust, Bebington, UK.
authors.forename: Isabel
authors.initials: I
authors.lastname: Syndikus
mesh_terms: D000368:Aged; D002794:Choline / Q000031:analogs & derivatives*; D006801:Humans; D008297:Male; D008875:Middle Aged; D000072078:Positron Emission Tomography Computed Tomography / Q000379:methods*; D011467:Prostate / Q000000981:diagnostic imaging / Q000473:pathology; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D016896:Treatment Outcome; D047368:Tumor Burden
chemical_list: C448902:fluoroethylcholine; D002794:Choline