Radiation Dosimetry of ⁸²Rb in Humans Under Pharmacologic Stress

Abstract

82Rb is used with PET for cardiac perfusion studies. Using human biokinetic measurements, in vivo, we recently reported on the resting-state dosimetry of this agent. The objective of this study was to obtain 82Rb dose estimates under stress. Methods 82Rb biokinetics were obtained in 10 healthy volunteers (5 male, 5 female; mean age ± SD, 33 ± 10 y; age range, 18–50 y) using whole-body PET/CT. The 76-s half-life of 82Rb and the corresponding need for pharmacologic vasodilation require that all imaging be completed within 10 min. To accommodate these constraints, while acquiring the data needed for dosimetry we used the following protocol. First, a whole-body attenuation correction CT scan was obtained. Then, a series of 3 whole-body PET scans was acquired after a single infusion of 1.53 ± 0.12 GBq of 82Rb at rest. Four minutes after the infusion of a 0.56 mg/kg dose of the vasodilator, dipyridamole, 3 serial whole-body PET scans were acquired after a single infusion of 1.50 ± 0.16 GBq of 82Rb under stress. The time-integrated activity coefficient (TIAC) for stress was obtained by scaling the mean rest TIAC obtained from our previous rest study by the stress-to-rest TIAC ratio obtained from the rest–stress measurements described in this report. Results The highest mean organ-absorbed doses under stress were as follows: heart wall, 5.1, kidneys, 5.0, lungs, 2.8, and pancreas, 2.4 μGy/MBq (19, 19, 10.4, and 8.9 mrad/mCi, respectively). The mean effective doses under stress were 1.14 ± 0.10 and 1.28 ± 0.10 μSv/MBq using the tissue-weighting factors of the International Commission on Radiological Protection, publications 60 and 103, respectively. Conclusion Appreciable differences in source-organ biokinetics were observed for heart wall and kidneys during stress when compared with the previously reported rest study. The organ receiving the highest dose during stress was the heart wall. The mean effective dose calculated during stress was not significantly different from that obtained at rest.

ASNC imaging guidelines/SNMMI procedure standard for positron emission tomography (PET) nuclear cardiology procedures

“…The radiation dosimetry from 82 Rb in an adult may vary from 1.1 to 3.5 mSv total effective dose for a maximal allowable activity of 60 mCi injection for each rest and stress study. 38,39 With current advances in PET instrumentation, diagnostic quality PET images can be acquired using only 20 to 40 mCi of 82 Rb for each of the rest and stress images of the study resulting in lower radiation exposure.…”

Production and Selection of Metal PET Radioisotopes for Molecular Imaging

“…Heart, kidney, lungs and pancreas receive an absorbed radiation dose of 5.1, 5.0, 2.8 and 2.4 mGy per MBq, respectively. This is significantly less than both 201 Tl and 99m Tc sestamibi SPECT agents (Senthamizhchelvan, S. et al, 2011). The long half life of the parent 82 Sr (t 1/2 = 25.55 days) permits its transport throughout the world.…”

Current Status of Myocardial Perfusion PET in the United States

“…A typical rest/stress Tc-99m SPECT exposes a patient to about 12 mSv of radiation, compared to about 3 for a rest/stress PET study (13)(14)(15). This is an important consideration for younger patients, and for those with chronic CAD who are likely to receive high radiation burdens during their years of coping with this chronic disease.…”