title: Estimating (131)I biokinetics and radiation doses to the red marrow and whole body in thyroid cancer patients: probe detection versus image quantification.
abstract: OBJECTIVE
  To compare the probe detection method with the image quantification method when estimating (131)I biokinetics and radiation doses to the red marrow and whole body in the treatment of thyroid cancer patients.
  
  
  METHODS
  Fourteen patients with metastatic thyroid cancer, without metastatic bone involvement, were submitted to therapy planning in order to tailor the therapeutic amount of (131)I to each individual. Whole-body scans and probe measurements were performed at 4, 24, 48, 72, and 96 h after (131)I administration in order to estimate the effective half-life (Teff) and residence time of (131)I in the body.
  
  
  RESULTS
  The mean values for Teff and residence time, respectively, were 19 ± 9 h and 28 ± 12 h for probe detection, compared with 20 ± 13 h and 29 ± 18 h for image quantification. The average dose to the red marrow and whole body, respectively, was 0.061 ± 0.041 mGy/MBq and 0.073 ± 0.040 mGy/MBq for probe detection, compared with 0.066 ± 0.055 mGy/MBq and 0.078 ± 0.056 mGy/MBq for image quantification. Statistical analysis proved that there were no significant differences between the two methods for estimating the Teff (p = 0.801), residence time (p = 0.801), dose to the red marrow (p = 0.708), and dose to the whole body (p = 0.811), even when we considered an optimized approach for calculating doses only at 4 h and 96 h after (131)I administration (p > 0.914).
  
  
  CONCLUSIONS
  There is full agreement as to the feasibility of using probe detection and image quantification when estimating (131)I biokinetics and red-marrow/whole-body doses. However, because the probe detection method is inefficacious in identifying tumor sites and critical organs during radionuclide therapy and therefore liable to skew adjustment of the amount of (131)I to be administered to patients under such therapy, it should be used with caution.
authors.affiliation: PhD, Chief Medical Physicist, Instituto do Câncer do Estado de São Paulo Octavio Frias de Oliveira (Icesp), São Paulo, SP, Brazil.
authors.forename: José
authors.initials: J
authors.lastname: Willegaignon
authors.affiliation: Technologist, Instituto do Câncer do Estado de São Paulo Octavio Frias de Oliveira (Icesp), São Paulo, SP, Brazil.
authors.forename: Rogério Alexandre
authors.initials: RA
authors.lastname: Pelissoni
authors.affiliation: Technologist, Instituto do Câncer do Estado de São Paulo Octavio Frias de Oliveira (Icesp), São Paulo, SP, Brazil.
authors.forename: Beatriz Christine de Godoy Diniz
authors.initials: BC
authors.lastname: Lima
authors.affiliation: PhD, Assistant Professor, Radiology Department, Faculdade de Medicina da Universidade de São Paulo (FMUSP), São Paulo, SP, Brazil.
authors.forename: Marcelo Tatit
authors.initials: MT
authors.lastname: Sapienza
authors.affiliation: MD, Nuclear Physician, Instituto do Câncer do Estado de São Paulo Octavio Frias de Oliveira (Icesp), São Paulo, SP, Brazil.
authors.forename: George Barberio
authors.initials: GB
authors.lastname: Coura-Filho
authors.affiliation: MD, Radiologist Physician, Instituto do Câncer do Estado de São Paulo Octavio Frias de Oliveira (Icesp), São Paulo, SP, Brazil.
authors.forename: Marcelo Araújo
authors.initials: MA
authors.lastname: Queiroz
authors.affiliation: PhD, Full Professor, Radiology Department, Faculdade de Medicina da Universidade de São Paulo (FMUSP), São Paulo, SP, Brazil.
authors.forename: Carlos Alberto
authors.initials: CA
authors.lastname: Buchpiguel
keywords: Dosimetry; Iodine radioisotopes/therapeutic use; Radioisotopes/pharmacokinetics; Radiotherapy; Thyroid neoplasms