title: Early prediction of tumour response to PRRT. The sequential change of tumour-absorbed doses during treatment with 177Lu-octreotate.
abstract: [177Lu-DOTA0,Tyr3]-octreotate (177Lu-octreotate) in peptide receptor radionuclide therapy (PRRT) offers direct intra-therapeutic dosimetry. The aim of this study was to compare tumour and non-tumour parameters and assess intra-individual variations.
  
  
  METHODS
  Retrospective analysis of 53 consecutive PRRT treatment cycles (mean activity of 7.53 ± 0.46 GBq 177Lu-octreotate, intended four cycles at intervals of 10-14 weeks, standard nephroprotection) in 27 GEP NET patients. Extended planar dosimetry with serial whole-body imaging on selected, non-superimposed tumour and non-tumour regions; liver (LM), bone (BM), and other (OM) metastases. The per-cycle variation was compared with post-treatment response (CT/MRI three months post-treatment, modified SWOG criteria).
  
  
  RESULTS
  Residence time in tumor lesions (133-147 h) exceeded that in kidneys (93 h). Tumour-to-kidney absorbed dose ratios ranged from 14 to 28 (LM, BM, OM). Intra-individual per-cycle dose variation was insignificant for kidneys, but significant for metastases (LM, BM, and OM; p < 0.05). The mean per-cycle decrease of tumour absorbed dose (ΔD/A0[%]) was linked to morphologic response after PRRT. A mean decrease of >20% was predictive of a partial or minor remission in all 11 evaluable patients, while absent significant dose reduction indicated stable or progressive disease in 4/5 patients. The dose decrease was unrelated to volume effects and also observed for BM.
  
  
  CONCLUSIONS
  Besides confirmation of a favourable tumour-to-kidney parameter relation for 177Lu-octreotate, stepwise intra-lesional comparison seems to imply a prognostic impact of tumor dosimetry: The early per-cycle change ΔD/A0 between treatment cycles may predict the outcome after PRRT. Larger studies are needed to confirm this finding.
authors: Samer Ezziddin, MD, Department of Nuclear Medicine, University Hospital Bonn, Sigmund-Freud-Str. 25, 53105 Bonn, Germany, Tel. +49/(0)228/28 71 91 74, Fax +49/(0)228/28 79 01 91 74, E-mail: samer.ezziddin@ukb.uni-bonn.de.
authors: S
authors: S
authors: Ezziddin
authors: K
authors: K
authors: Reichmann
authors: C
authors: C
authors: Yong-Hing
authors: M
authors: M
authors: Damm
authors: J
authors: J
authors: Risse
authors: H
authors: H
authors: Ahmadzadehfar
authors: T
authors: T
authors: Logvinski
authors: S
authors: S
authors: Guhlke
authors: H-J
authors: HJ
authors: Biersack
authors: A
authors: A
authors: Sabet
mesh_terms: D000328:Adult; D000368:Aged; D004067:Digestive System Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D055088:Early Detection of Cancer / Q000379:methods*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015282:Octreotide / Q000031:analogs & derivatives* / Q000627:therapeutic use; D011379:Prognosis; D011874:Radiometry / Q000379:methods*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000627:therapeutic use; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016896:Treatment Outcome
chemical_list: C554548:177Lu-octreotate; D019275:Radiopharmaceuticals; D015282:Octreotide
keywords: 177Lu-DOTA octreotate; Gastroenteropancreatic neuroendocrine tumours; dosimetry; peptide receptor radionuclide therapy; tumour response