A dose-effect correlation for radioiodine ablation in differentiated thyroid cancer.
OBJECTIVE
The aim of this study was to determine the range of absorbed doses delivered to thyroid remnants, blood, and red marrow from fixed administrations of radioiodine and to ascertain whether the success of ablation is more dependent on these absorbed doses than on the administered activity.


METHODS
Twenty-three patients received 3,000 MBq radioiodine following near-total thyroidectomy. The maximum absorbed dose to remnants was calculated from subsequent single photon emission tomography scans. Absorbed doses delivered to blood and red marrow were calculated from blood samples and from whole-body retention measurements. The protein bound iodine (PBI) was also calculated.


RESULTS
Maximum absorbed doses to thyroid remnants ranged from 7 to 570 Gy. Eighteen of the 23 patients had a successful ablation. A significant difference was seen between the absorbed doses delivered to thyroid remnants, blood, and red marrow for those patients that had a successful ablation compared to those with a failed ablation (p = 0.030, p = 0.043 and p = 0.048, respectively). The difference between the PBI values acquired at day 1 and day 6 were also indicative of response (p = 0.074).


CONCLUSIONS
A successful ablation is strongly dependent on the absorbed dose to the thyroid remnant. Dosimetry-based personalized treatment can prevent both sub-optimal administrations, which entails further radioiodine therapy, and excessive administration of radioactivity, which increases the potential for radiation toxicity.
Flux
Glenn D
GD
Department of Physics, Royal Marsden NHS Foundation Trust, Sutton, Surrey, SM2 5PT, UK. glenn.flux@icr.ac.uk
Haq
Masud
M
Chittenden
Sarah J
SJ
Buckley
Susan
S
Hindorf
Cecilia
C
Newbold
Kate
K
Harmer
Clive L
CL
D000293:Adolescent; D000328:Adult; D000368:Aged; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D011874:Radiometry; D011877:Radionuclide Imaging; D011879:Radiotherapy Dosage; D012062:Relative Biological Effectiveness; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D055815:Young Adult
D007457:Iodine Radioisotopes