Katarina Sjögreen Gleisner
Professor
Whole-remnant and maximum-voxel SPECT/CT dosimetry in 131I-NaI treatments of differentiated thyroid cancer
Författare
Summary, in English
Purpose: To investigate the possible differences between SPECT/CT based whole-remnant and maximum-voxel dosimetry in patients receiving radio-iodine ablation treatment of differentiated thyroid cancer (DTC). Methods: Eighteen DTC patients were administered 1.11 GBq of 131I-NaI after near-total thyroidectomy and rhTSH stimulation. Two patients had two remnants, so in total dosimetry was performed for 20 sites. Three SPECT/CT scans were performed for each patient at 1, 2, and 3-7 days after administration. The activity, the remnant mass, and the maximum-voxel activity were determined from these images and from a recovery-coefficient curve derived from experimental phantom measurements. The cumulated activity was estimated using trapezoidal-exponential integration. Finally, the absorbed dose was calculated using S-values for unit-density spheres in whole-remnant dosimetry and S-values for voxels in maximum-voxel dosimetry. Results: The mean absorbed dose obtained from whole-remnant dosimetry was 40 Gy (range 2-176 Gy) and from maximum-voxel dosimetry 34 Gy (range 2-145 Gy). For any given patient, the activity concentrations for each of the three time-points were approximately the same for the two methods. The effective half-lives varied (R = 0.865), mainly due to discrepancies in estimation of the longer effective half-lives. On average, absorbed doses obtained from whole-remnant dosimetry were 1.2±0.2 (1 SD) higher than for maximum-voxel dosimetry, mainly due to differences in the S-values. The method-related differences were however small in comparison to the wide range of absorbed doses obtained in patients. Conclusions: Simple and consistent procedures for SPECT/CT based whole-volume and maximumvoxel dosimetry have been described, both based on experimentally determined recovery coefficients. Generally the results from the two approaches are consistent, although there is a small, systematic difference in the absorbed dose due to differences in the S-values, and some variability due to differences in the estimated effective half-lives, especially when the effective half-life is long. Irrespective of the method used, the patient absorbed doses obtained span over two orders of magnitude.
Avdelning/ar
- Medicinsk strålningsfysik, Lund
Publiceringsår
2016-10-01
Språk
Engelska
Sidor
5279-5287
Publikation/Tidskrift/Serie
Medical Physics
Volym
43
Issue
10
Dokumenttyp
Artikel i tidskrift
Förlag
American Association of Physicists in Medicine
Ämne
- Radiology, Nuclear Medicine and Medical Imaging
- Other Physics Topics
Nyckelord
- I-NaI
- differentiated thyroid carcinoma
- dosimetry
- thyroid bed remnants
Status
Published
ISBN/ISSN/Övrigt
- ISSN: 0094-2405