title: Challenges in using ¹⁸F-fluorodeoxyglucose-PET-CT to define a biological radiotherapy boost volume in locally advanced pancreatic cancer.
abstract: BACKGROUND
  The best method of identifying regions within pancreatic tumours that might benefit from an increased radiotherapy dose is not known. We investigated the utility of pre-treatment FDG-PET in predicting the spatial distribution of residual metabolic activity following chemoradiotherapy (CRT) in locally advanced pancreatic cancer (LAPC).
  
  
  METHODS
  17 patients had FDG-PET/CT scans at baseline and six weeks post-CRT. Tumour segmentation was performed at 40% and 50% of SUVmax at baseline and 60%, 70%, 80% and 90% post-CRT. FDG-PET scans were non-rigidly registered to the radiotherapy planning CT using the CT component of the FDG-PET/CT. Percentage overlap of the post-CRT volumes with the pre-CRT volumes with one another and the gross tumour volume (GTV) was calculated.
  
  
  RESULTS
  SUVmax decreased during CRT (median pre- 8.0 and post- 3.6, p < 0.0001). For spatial correlation analysis, 9 pairs of scans were included (Four were excluded following complete metabolic response, one patient had a non-FDG avid tumour, one had no post-CRT imaging, one had diffuse FDG uptake that could not be separated from normal tissues and one had an elevated blood glucose). The Pre40% and 50% of SUVmax volumes covered a mean of 50.8% and 30.3% of the GTV respectively. The mean% overlap of the 90%, 80%, 70%, 60% of SUVmax post-CRT with the Pre40% and Pre50% volumes were 83.3%, 84.0%, 83.7%, 77.9% and 77.8%, 69.9%, 74.5%, 64.8% respectively.
  
  
  CONCLUSIONS
  Regions of residual metabolic activity following CRT can be predicted from the baseline FDG-PET and could aid definition of a biological target volume for non-uniform dose prescriptions.
authors: CRUK/MRC Oxford Institute for Radiation Oncology, Gray Laboratories, University of Oxford, Old Road Campus Research Building, Off Roosevelt Drive, Oxford OX3 7DQ, UK. james.wilson@oncology.ox.ac.uk.
authors: James M
authors: JM
authors: Wilson
authors: Somnath
authors: S
authors: Mukherjee
authors: Kwun-Ye
authors: KY
authors: Chu
authors: Thomas B
authors: TB
authors: Brunner
authors: Mike
authors: M
authors: Partridge
authors: Maria
authors: M
authors: Hawkins
mesh_terms: D000230:Adenocarcinoma / Q000175:diagnosis / Q000378:metabolism / Q000628:therapy; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D059248:Chemoradiotherapy; D002945:Cisplatin / Q000008:administration & dosage; D017322:Clinical Trials, Phase II as Topic; D003841:Deoxycytidine / Q000008:administration & dosage / Q000031:analogs & derivatives; D019788:Fluorodeoxyglucose F18; D005500:Follow-Up Studies; D006801:Humans; D064847:Multimodal Imaging; D009367:Neoplasm Staging; D010190:Pancreatic Neoplasms / Q000175:diagnosis* / Q000378:metabolism / Q000628:therapy*; D049268:Positron-Emission Tomography / Q000706:statistics & numerical data*; D011379:Prognosis; D019275:Radiopharmaceuticals; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data*; D000093542:Gemcitabine
chemical_list: D019275:Radiopharmaceuticals; D003841:Deoxycytidine; D019788:Fluorodeoxyglucose F18; D002945:Cisplatin; D000093542:Gemcitabine