title: Discrepant salivary gland response after radioiodine and MIBG therapies.
abstract: BACKGROUND
  A retrospective study using PET/CT imaging with 124I-labeled metaiodobenzylguanidine (124I-MIBG) was performed to estimate the (radiation) absorbed dose to the salivary glands in neuroendocrine cancer patients undergoing 131I-MIBG therapy and to compare these results with those in radioiodine (131I-iodide) therapy.
  
  
  METHODS
  Twenty-seven patients received individual 124I-MIBG-PET/CT dosimetries, among whom 18 had not previously undergone any MIBG therapies (patient group before treatment) and 9 had already received MIBG therapies prior to the tracer dosimetries (patient group after treatment). For each patient, three or four 124I-MIBG PET/CT scans were performed at approximately 4 and 24 hours, as well as at approximately 48 or/and ≥96 hours after tracer injection. The absorbed doses per administered 131I-MIBG activity to the submandibular and parotid glands were calculated based on the MIRD concept, with its assumption of a uniform glandular activity distribution.
  
  
  RESULTS
  The mean±standard deviation of the (self-)absorbed dose per activity averaged over both patient groups and salivary gland types was 0.53±0.24 Gy/GBq (median, 0.49 Gy/GBq; range, 0.17-1.38 Gy/GBq). The absorbed doses per activity of the patient group before treatment did not significantly deviate from those of the patient group after treatment (P=0.67). In the patient group after treatment, the mean±standard deviation of the cumulative 131I-MIBG activity was 20±12 GBq (median, 16 GBq; range, 10-50 GBq). Among the patient groups, no significant absorbed dose difference was found between the submandibular and parotid glands (P>0.24). In comparison to radioiodine therapy, the estimated absorbed dose per activity in MIBG was significantly higher (P<0.001), on average twice as high, contradicting the relationship between the absorbed dose and clinical observation of glandular side effects.
  
  
  CONCLUSIONS
  The discrepant salivary gland responses in MIBG and radioiodine therapies suggest a different radiotherapeutical distribution on microscopic scale within the glandular tissue and prove the clinical relevance of a microdosimetric analysis.
authors.affiliation: Nuclear Medicine Clinic, Duisburg-Essen University, Essen, Germany - walter.jentzen@uni-duisburg-essen.de.
authors.forename: Walter
authors.initials: W
authors.lastname: Jentzen
authors.affiliation: Nuclear Medicine Clinic, Duisburg-Essen University, Essen, Germany.
authors.forename: Marion
authors.initials: M
authors.lastname: Richter
authors.affiliation: Nuclear Medicine Clinic, Duisburg-Essen University, Essen, Germany.
authors.forename: Thorsten D
authors.initials: TD
authors.lastname: Poeppel
authors.affiliation: Nuclear Medicine Clinic, Duisburg-Essen University, Essen, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Schmitz
authors.affiliation: Nuclear Medicine Clinic, Duisburg-Essen University, Essen, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Brandau
authors.affiliation: Nuclear Medicine Clinic, Duisburg-Essen University, Essen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Bockisch
authors.affiliation: Nuclear Medicine Clinic, Duisburg-Essen University, Essen, Germany.
authors.forename: Ina
authors.initials: I
authors.lastname: Binse
mesh_terms: D019797:3-Iodobenzylguanidine / Q000009:adverse effects* / Q000627:therapeutic use; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D018278:Carcinoma, Neuroendocrine / Q000000981:diagnostic imaging / Q000532:radiotherapy; D002648:Child; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000009:adverse effects* / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D000072078:Positron Emission Tomography Computed Tomography; D011829:Radiation Dosage; D012189:Retrospective Studies; D012469:Salivary Glands / Q000000981:diagnostic imaging / Q000528:radiation effects*; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes; C000614965:Iodine-131; D019797:3-Iodobenzylguanidine