OBJECTIVE: The present study was aimed at evaluating the viability of replacing ¹⁸F with ^99mTc in dose calibrator linearity testing. MATERIALS AND METHODS: The test was performed with sources of ^99mTc (62 GBq) and ¹⁸F (12 GBq) whose activities were measured up to values lower than 1 MBq. Ratios and deviations between experimental and theoretical ^99mTc and ¹⁸F sources activities were calculated and subsequently compared. RESULTS: Mean deviations between experimental and theoretical ^99mTc and ¹⁸F sources activities were 0.56 (± 1.79)% and 0.92 (± 1.19)%, respectively. The mean ratio between activities indicated by the device for the ^99mTc source as measured with the equipment pre-calibrated to measure ^99mTc and ¹⁸F was 3.42 (± 0.06), and for the ¹⁸F source this ratio was 3.39 (± 0.05), values considered constant over the measurement time. CONCLUSION: The results of the linearity test using ^99mTc were compatible with those obtained with the ¹⁸F source, indicating the viability of utilizing both radioisotopes in dose calibrator linearity testing. Such information in association with the high potential of radiation exposure and costs involved in ¹⁸F acquisition suggest ^99mTc as the element of choice to perform dose calibrator linearity tests in centers that use ¹⁸F, without any detriment to the procedure as well as to the quality of the nuclear medicine service.

Keywords: Nuclear medicine; Dose calibrator; Linearity test; Nuclear instrumentation.

OBJECTIVE: To analyze standardized uptake values (SUVs) using three different tube current intensities for attenuation correction on ¹⁸FNaF PET/CT scans. MATERIALS AND METHODS: A total of 254 ¹⁸F-NaF PET/CT studies were analyzed using 10, 20 and 30 mAs. The SUVs were calculated in volumes of interest (VOIs) drawn on three skeletal regions, namely, right proximal humeral diaphysis (RH), right proximal femoral diaphysis (RF), and first lumbar vertebra (LV1) in a total of 712 VOIs. The analyses covered 675 regions classified as normal (236 RH, 232 RF, and 207 LV1). RESULTS: Mean SUV for each skeletal region was 3.8, 5.4 and 14.4 for RH, RF, and LV1, respectively. As the studies were grouped according to mAs value, the mean SUV values were 3.8, 3.9 and 3.7 for 10, 20 and 30 mAs, respectively, in the RH region; 5.4, 5.5 and 5.4 for 10, 20 and 30 mAs, respectively, in the RF region; 13.8, 14.9 and 14.5 for 10, 20 and 30 mAs, respectively, in the LV1 region. CONCLUSION: The three tube current values yielded similar results for SUV calculation.

Keywords: ¹⁸F-NaF PET/CT; SUV; Tube current; mAs.

OBJECTIVE: To assess the cutoff values established by ROC curves to classify ¹⁸F-NaF uptake as normal or malignant. MATERIALS AND METHODS: PET/CT images were acquired 1 hour after administration of 185 MBq of ¹⁸F-NaF. Volumes of interest (VOIs) were drawn on three regions of the skeleton as follows: proximal right humerus diaphysis (HD), proximal right femoral diaphysis (FD) and first vertebral body (VB1), in a total of 254 patients, totalling 762 VOIs. The uptake in the VOIs was classified as normal or malignant on the basis of the radiopharmaceutical distribution pattern and of the CT images. A total of 675 volumes were classified as normal and 52 were classified as malignant. Thirty-five VOIs classified as indeterminate or nonmalignant lesions were excluded from analysis. The standardized uptake value (SUV) measured on the VOIs were plotted on an ROC curve for each one of the three regions. The area under the ROC (AUC) as well as the best cutoff SUVs to classify the VOIs were calculated. The best cutoff values were established as the ones with higher result of the sum of sensitivity and specificity. RESULTS: The AUCs were 0.933, 0.889 and 0.975 for UD, FD and VB1, respectively. The best SUV cutoffs were 9.0 (sensitivity: 73%; specificity: 99%), 8.4 (sensitivity: 79%; specificity: 94%) and 21.0 (sensitivity: 93%; specificity: 95%) for UD, FD and VB1, respectively. CONCLUSION: The best cutoff value varies according to bone region of analysis and it is not possible to establish one value for the whole body.

Keywords: ¹⁸F-NaF PET/CT; ROC curve; Cutoff values; Normal uptake; Malignant uptake

OBJECTIVE: To compare the probe detection method with the image quantification method when estimating ¹³¹I biokinetics and radiation doses to the red marrow and whole body in the treatment of thyroid cancer patients. MATERIALS AND METHODS: Fourteen patients with metastatic thyroid cancer, without metastatic bone involvement, were submitted to therapy planning in order to tailor the therapeutic amount of ¹³¹I to each individual. Whole-body scans and probe measurements were performed at 4, 24, 48, 72, and 96 h after ¹³¹I administration in order to estimate the effective half-life (T_eff) and residence time of ¹³¹I in the body. RESULTS: The mean values for T_eff and residence time, respectively, were 19 ± 9 h and 28 ± 12 h for probe detection, compared with 20 ± 13 h and 29 ± 18 h for image quantification. The average dose to the red marrow and whole body, respectively, was 0.061 ± 0.041 mGy/MBq and 0.073 ± 0.040 mGy/MBq for probe detection, compared with 0.066 ± 0.055 mGy/MBq and 0.078 ± 0.056 mGy/MBq for image quantification. Statistical analysis proved that there were no significant differences between the two methods for estimating the T_eff (p = 0.801), residence time (p = 0.801), dose to the red marrow (p = 0.708), and dose to the whole body (p = 0.811), even when we considered an optimized approach for calculating doses only at 4 h and 96 h after ¹³¹I administration (p > 0.914). CONCLUSION: There is full agreement as to the feasibility of using probe detection and image quantification when estimating ¹³¹I biokinetics and red-marrow/whole-body doses. However, because the probe detection method is inefficacious in identifying tumor sites and critical organs during radionuclide therapy and therefore liable to skew adjustment of the amount of ¹³¹I to be administered to patients under such therapy, it should be used with caution.

Keywords: Thyroid neoplasms; Iodine radioisotopes/therapeutic use; Radioisotopes/pharmacokinetics; Dosimetry; Radiotherapy.

OBJECTIVE: To compare the degree of benign bone marrow uptake of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) between Hodgkin lymphoma patients with and without B symptoms. MATERIALS AND METHODS: We analyzed the medical charts of 74 Hodgkin lymphoma patients who underwent ¹⁸F-FDG positron emission tomography/computed tomography (PET/CT) prior to the initiation of therapy between October 2010 and September 2013. In all of the patients, the bone marrow biopsy was negative and the ¹⁸F-FDG PET/CT images did not suggest bone marrow involvement. Of the 74 patients evaluated, 54 presented inflammatory (B) symptoms and 20 did not. Regions of interest (ROIs) were drawn on the sternum, the proximal thirds of the humeri, the proximal thirds of the femora, and both iliac wings (totaling seven ROIs per patient). To compare the patients with and without B symptoms, in terms of standardized uptake values (SUVs) for the seven ROIs, we used the Mann-Whitney U test. RESULTS: For six of the ROIs, the SUVs were higher in the patients with B symptoms than in those without, and the difference was statistically significant (p < 0.05). There was also a tendency toward a statistically significant difference between the two groups in terms of the SUV for the right iliac wing ROI (p = 0.06). CONCLUSION: In our sample, the presence of B symptoms was associated with increased ¹⁸F-FDG uptake in bone marrow.

Keywords: Keywords: Fluorodeoxyglucose F18; Positron emission tomography computed tomography/methods; Hodgkin disease; Bone marrow/diagnostic imaging.