18F--tetrafluoroborate (18F--TFB), a PET probe for imaging sodium-iodide symporter expression: Whole-body biodistribution, safety and radiation dosimetry in thyroid cancer patients

Abstract

Rationale

We report the safety, biodistribution and internal radiation dosimetry, in humans with thyroid cancer, of 18F-tetrafluoroborate (18F-TFB), a novel PET radioligand for imaging the human sodium/iodide symporter (hNIS).

Methods

Serial whole-body PET scans of 5 subjects with recently diagnosed with thyroid cancer were acquired prior to surgery for up to 4 hours after injection of 184 ± 15 MBq of 18F-TFB. Activity was determined in whole blood, plasma and urine. Mean organ absorbed doses and effective doses were calculated via quantitative image analysis and using OLINDA/EXM software.

Results

Images showed high uptake of 18F-TFB in known areas of high hNIS expression (thyroid, salivary glands and stomach). Excretion was predominantly renal. No adverse effects in relation to safety of the radiopharmaceutical were observed. The effective dose was 0.0326 ± 0.0018 mSv/MBq. The critical tissues/organs receiving the highest mean sex-averaged absorbed doses were thyroid (0.135 ± 0.079 mSv/MBq), stomach (0.069 ± 0.022 mSv/MBq) and salivary glands (parotids 0.031 ± 0.011 mSv/MBq, submandibular 0.061 ± 0.031 mSv/MBq). Other organs of interest were the bladder (0.102 ± 0.046 mSv/MBq) and kidneys (0.029 ± 0.009 mSv/MBq).

Conclusion

Imaging using 18F-TFB imparts a radiation exposure similar in magnitude to many other 18F--labeled radiotracers. 18F-TFB shows a similar biodistribution to 99mTc-pertechnetate, a known non-organified hNIS tracer, and is pharmacologically and radiobiologically safe in humans. Phase 2 trials as a hNIS imaging agent are warranted.