Determining the Minimal Required Radioactivity of ¹⁸F-FDG for Reliable Semiquantification in PET/CT Imaging: A Phantom Study

Abstract

In pursuit of as-low-as-reasonably-achievable (ALARA) doses, this study investigated the minimal required radioactivity and corresponding imaging time for reliable semiquantification in PET/CT imaging. Methods: Using a phantom containing spheres of various diameters (3.4, 2.1, 1.5, 1.2, and 1.0 cm) filled with a fixed 18 F-FDG concentration of 165 kBq/mL and a background concentration of 23.3 kBq/mL, we performed PET/CT at multiple time points over 20 h of radioactive decay. The images were acquired for 10 min at a single bed position for each of 10 half-lives of decay using 3-dimensional list mode and were reconstructed into 1-, 2-, 3-, 4-, 5-, and 10-min acquisitions per bed position using an ordered-subsets expectation maximum algorithm with 24 subsets and 2 iterations and a gaussian 2-mm filter. SUV max and SUV avg were measured for each sphere. Results: The minimal required activity (±10%) for precise SUV max semiquantification in the spheres was 1.8 kBq/mL for an acquisition of 10 min, 3.7 kBq/mL for 3-5 min, 7.9 kBq/mL for 2 min, and 17.4 kBq/mL for 1 min. The minimal required activity concentration-acquisition time product per bed position was 10-15 kBq/mL⋅min for reproducible SUV measurements within the spheres without overestimation. Using the total radioactivity and counting rate from the entire phantom, we found that the minimal required total activity-time product was 17 MBq⋅min and the minimal required counting rate-time product was 100 kcps⋅min. Conclusion: Our phantom study determined a threshold for minimal radioactivity and acquisition time for precise semiquantification in 18 F-FDG PET imaging that can serve as a guide in pursuit of achieving ALARA doses.Key Words: PET; phantom; dosimetry; dose reduction; acquisition time; standard uptake value J Nucl Med Technol 2016; 44:26-30 DOI: 10.2967/jnmt.115.165258 There is a growing trend to minimize ionizing radiation exposure, particularly from diagnostic medical imaging involving x-rays and internal radiation from administration of radionuclides. Recent evidence from a retrospective largecohort study of over 178,600 U.K. residents who were exposed to radiation from CT scans in childhood found that a cumulative dose of more than 30 mGy to red bone marrow from as few as 5-10 head CT scans in children younger than 15 y carried a relative risk of 3.18 for leukemia as compared with a cumulative dose of less than 5 mGy. For brain cancer, a cumulative dose of 50-74 mGy to brain from as few as 2-3 head CT scans carried a relative risk of 2.82, as compared with those receiving a cumulative dose of less than 5 mGy (1). In a study of 680,000 Australians exposed to CT scans in childhood and adolescence, Mathews et al. found an incidence rate ratio of 1.24 for all cancers, with an observed dose-response relation of 0.16 per additional CT scan using an estimated average effective radiation dose of 4.5 mSv per scan (2).18 F-FDG PET/CT has been widely used for oncologic and cardiac imaging, with radiation exposure being derived from the injected dose of radiot...

Reduction of the fluorine-18-labeled fluorodeoxyglucose dose for clinically dedicated breast positron emission tomography

“…This is considered to be a severe partial-volume effect in small spheres. These results were consistent with the previous phantom study of PET/CT on 18 F-FDG dose reduction [10]. Furthermore, the SUV max and SUV mean were underestimated at very low dose of about 5% or less, possibly due to excessive scatter correction.…”

“…PET/CT results in considerable radiation exposure (approximately 7–10 mSv in recent studies, derived from the injected dose of radiotracer and X-ray CT used for attenuation correction and anatomic co-registration) [7, 8]. Exposure reduction is a major concern in PET, and several studies have reported on dose reduction of 18F-FDG in PET/CT [9, 10] or PET/magnetic resonance (PET/MR) [11–13]. By combining long acquisition (20 min) of breast regions on PET/MR system with high sensitivity detector consisting of silicon photomultiplier, the radiation exposure was successfully reduced comparable to the effective dose of a single digital mammogram [13].…”

Minimal-activity PET/CT for efficacy control after SIRT (MAPECSI) – clinical implementation of a resource-saving, liver-focused protocol

“…For special indications, like the differential diagnosis of a solitary pulmonary nodule, tailored imaging strategies like segmental PET/CT scans of dedicated regions were suggested to reduce financial or radiation burden [19,20]. The option of a minimal-activity PET/CT was evaluated in a phantom study and in clinical practice, compensating the reduced amount of radiotracer with a prolonged acquisition time [21,22]. Considering the continually increasing number of SIRT procedures and nuclear medicine examinations, even fully equipped departments reach their capacity limits and are forced to improve their processes.…”

Effect of urinary excretion on radiation dose in patients having PET/CT scans

“…Image fusion technology, for example, can further reduce radiation exposure [18]. Based on ALARA principle, the present study investigated minimal radioactivity level and corresponding imaging time required for reliable semiquantification in PET/CT imaging [19] cumulative 18F-FDG dose was calculated in milli-Curies during treatment and surveillance of all patients who received PET/CT scans. Calculated 18F-FDG PET/CT dose was converted to effective dose from milli-Curies to Becquerels and then from Becquerels to milli-Sieverts using a conversion factor of 0.019 mSv/MBq [20].…”