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Advances in Radiotherapy
& Nuclear Medicine Exploring F-FDG PET/CT in Richter transformation
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its ability to distinguish RT with high negative predictive fused PET/CT images at a combined reading session. The
value and identify sites of increased F-FDG uptake that is fused PET/CT images were used primarily for localizing
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suitable for biopsy. This study aimed to precisely evaluate lesions and differentiating abnormal metabolic activity
the positive and negative predictive values and predict the from physiological F-FDG uptake within adjacent organs.
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most affected lymph node sites, which can be validated Metabolic activity within sites of abnormal F-FDG uptake
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with histopathological confirmation. was analyzed qualitatively and semi-quantitatively on the PET
images. The determination of the standardized uptake value
2. Methods (SUVmax) within the volume of interest followed the formula:
2.1. Patient recruitment SUVmax = (Measured activity within the volume of
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A retrospective analysis of consecutive CLL patients who interest in MBq/mL)/(Injected dose of F-FDG
underwent F-FDG PET/CT at our institution between in MBq)/(Patient’s body weight in g) (I)
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November 2018 and December 2022 was performed. The The accuracy and consistency of SUV measurements
indication for PET/CT was suspicion of RST. F-FDG with F-FDG PET/CT were maintained by our in-house
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PET/CT was considered for patients with CLL presented quality control program. The program is performed by our
with elevated lactate dehydrogenase (LDH) levels, enlarged service team weekly and relies on the use of radioactive
lymph node, and fever in the absence of infection. Patients 18 F-containing sources and calibration phantoms (i.e., for
were excluded from the study if they had not undergone replicating human tissues), adherence to standardized
bone marrow or lymph node biopsy after a positive protocols, in-depth result analysis, and ongoing training
PET/CT (e.g., patients with high suspicion of RT requiring of personnel to maintain optimal performance. These
urgent treatment). practices allow for meticulous monitoring of equipment
performance, ensuring measurement fidelity and obtaining
2.2. F-fluorodeoxyglucose positron emission reliable results during medical imaging examinations.
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tomography-computed tomography imaging
On the PET/CT images, sites of abnormal F-FDG
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All F-FDG PET/CT scans were performed on an integrated uptake were documented with respect to the intensity of
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PET/CT scanner (GE Discovery STE8, GE Healthcare, the uptake and its anatomic location, and these parameters
USA). The patients fasted for at least 8 h before undergoing were then compared to the F-FDG intensity in the liver,
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scanning with any premedication. Blood glucose levels and with values ranging from 2.4 to 4.5 and a mean value of
body weight were measured shortly before the injection. 3.2. In our study, an SUVmax >5 within a lymph node or
All patients had blood glucose levels below 6.27 mmol/L.
Image acquisition was conducted 45 – 60 min after extranodal site was considered suggestive of RT, whereas
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intravenous injection with a net dose of 3 MBq/kg of F- SUVmax <5 indicated a more indolent phase of CLL.
A cutoff SUVmax = 5 was chosen empirically based on
FDG and an average uptake time of 50 min. The mean net our institutional practice and other similar studies.
3,4
injected F-FDG dose, calculated based on body weights Extranodal disease was suspected if abnormal F-FDG
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ranging from 50 to 80 kg and excluding residual activity in uptake was observed within an extranodal soft-tissue mass
the syringe, was 193 MBq.
or in the liver, spleen, bone marrow, or another organ.
PET/CT images were acquired from the head to the The F-FDG PET/CT findings were then correlated with
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upper thighs for 3 min per bed position. PET images histological findings from the bone marrow or lymph node
were reconstructed using standard vendor-provided biopsies performed on patients with positive PET/CT.
reconstruction algorithms, which incorporated ordered-
subset expectation maximization, including the two 2.3. Histopathological and descriptive analyses
iterations, 28 subsets, and a 128 × 128 reconstruction Histopathological examination is the gold standard for the
matrix. PET images were subjected to attenuation diagnosis of RT and was used in this study for patients with
correction using data from the CT component of the positive PET/CT. Biopsy was performed either on the lymph
examination. CT examination covering the area from nodes, extranodal site, or the bone marrow. Descriptive
the skull base to the upper thighs was performed using analyses of the patient’s age, sex, and the nodal and extranodal
the following parameters: 120 mA for current intensity sites of increased uptake were performed accordingly.
and 140 kVp for voltage, with a table speed of 13.5 mm/
rotation. Axial CT images were reconstructed with a 3. Results
section thickness of 3.75 mm. A total of 12 patients suspected of RT were included in our
All PET/CT studies were reviewed by two nuclear study. Their mean age at the time of their F-FDG PET/
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physicians. Both physicians examined the PET, CT, and CT scan was 66 years (range: 53 – 76 years). There was a

Volume 2 Issue 1 (2024) 2 https://doi.org/10.36922/arnm.2431