Effect of androgen deprivation therapy on intraprostatic tumour volume identified on 18 F choline PET/CT for prostate dose painting radiotherapy

• Published in: British journal of radiology 2017-03, Vol.90 (1071), p.20160818
• Main Authors: Chan, Joachim, Carver, Antony, Brunt, John N H, Vinjamuri, Sobhan, Syndikus, Isabel
• Format: Article
• Language: English
• Subjects: Aged; Choline - analogs & derivatives; Humans; Male; Middle Aged; Positron Emission Tomography Computed Tomography - methods; Prostate - diagnostic imaging; Prostate - pathology; Prostatic Neoplasms - pathology; Prostatic Neoplasms - radiotherapy; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; Radiotherapy, Intensity-Modulated - methods; Retrospective Studies; Treatment Outcome; Tumor Burden
• ISSN: 1748-880X

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. Fluoroethylcholine ( F 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 (SUV ) 60%] when compared with mpMRI. 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 SUV was 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. For visual contouring of boost volumes in prostate dose painting radiotherapy, F 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 SUV may 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 of F 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.