US-guided percutaneous ablation of thyroid nodules with 177LU-MAA (LUTMA) - Feasibility study.

PURPOSE: The main purpose is to evaluate the safety, and efficacy of 177Lutetium labeled macroaggregated albumin (LUTMA) ablation of thyroid nodules. MATERIALS AND METHODS: Patients with confirmed benign nodules who were not candidate or did not accept surgery were enrolled. Under ultrasonography (USG) guidance, LUTMA which was produced in our department, was administered into the nodules. Nodule volumes were assessed via USG before the injection and at 1-week, 1-month, and 3-months post-treatment. We calculated the volume reduction rates (VRRs) for these intervals. To detect extranodular activity leakage, patients underwent SPECT/CT imaging at one hour, 24 h, and one week post-injection. RESULTS: Fifteen patients (male: 12, female: 3) with benign thyroid nodules were eligible to join this study. These nodules were categorized as cystic (n = 9), solid (n = 3), or mixed (n = 3). Median nodules volume was 6.59 ml (range: 0.56-55 ml). Predicted absorbed dosee to the nodules varied between 10-1036 Gy. The VRRs at 3 months was 85% for all nodule types with gradual increases over time: 0%-92%, 20%-97%, and 28%-98% at 1 week, 1 month, and 3-months, respectively. The median VRR of cystic nodules was 89% (range: 81%-98%) at 3-months. It is significantly higher than solid ones (P = .009). None of the patients experienced adverse reactions or discomfort during the injection or follow-up. CONCLUSION: LUTMA treatment significantly reduces the volume of benign thyroid nodules, offering relief from disease-associated symptoms and cosmetic concerns. It emerges as a promising alternative to surgical and other local treatments for benign thyroid nodule ablation. CLINICAL SIGNIFICATION: LUTMA is a novel theranostic radiopharmaceutical which is promising in local ablative treatment of benign thyroid nodules.

A multi-institutional assessment of eye lens dose in nuclear medicine clinics.

AIM: The endeavor was to measure the lens dose of actively working staff in nuclear medicine departments. MATERIAL AND METHODS: This study was accomplished in three nuclear medicine sites. A total of 23 workers in nuclear medicine joined this work. Among them are 6 SPECT/ CT technologists, 6 PET/CT technologists, 3 PET/MRI technologists, 5 radiopharmacists, 2 physicists, and 1 physician. EXTDOSE Hp(3) OSL dosimeter with tissue equivalent beryllium-oxide crystal was used for lens dose measurement. All participants were asked to wear the lens dosimeter for 2 months as near to the eye level as possible. RESULTS: Pooling the dose measures together yielded an average lens dose of 1.48 ±â€…0.77 mSv for the radiopharmacy team, 1.44 ±â€…0.26 for PET/ CT technologists, 0.86 ±â€…0.45 mSv for SPECT/ CT technologists, 0.38 mSv for the sole physician administered 177Lu, and 0.45 ±â€…0.02 mSv for the physicists conducting 131I therapy. Moreover, normalizing the lens dose to the labeled activity led to a lens dose of 2.2 ±â€…1.4 µSv/GBq for the radiopharmacy team. Likewise, per administered activity: 23.8 ±â€…7.3 µSv/GBq for PET/CT and PET/MRI technologists, 12.2 ±â€…10.5 µSv/GBq 99mTc for SPECT/CT technologists, 6.0 ±â€…0.81 µSv/GBq 131I for physicists, and 3.0 µSv/GBq 177Lu for the physician. CONCLUSION: It was deduced that the annual occupational lens dose of the nuclear medicine workers varied from 2.3 to 11.5 mSv/year; however, one radiopharmacist projected annual lens dose as close to the lens equivalent dose limit (20 mSv/year) as 17.9 mSv.

Assessment of PET/CT: National Electrical Manufacturers Association NU2-2018 Standards versus American Association of Physicists in Medicine Task Group 126.

OBJECTIVE: The aim of this study was to perform and evaluate PET/computed tomography acceptance tests separately using American Association of Physicists in Medicine (AAPM) Task Group 126 and National Electrical Manufacturers Association (NEMA) methods. MATERIALS AND METHODS: Measurements of sensitivity, spatial resolution, count rate performance and scatter fraction, the accuracy of corrections for count losses and randoms, and image quality were obtained according to NEMA NU-2018. Likewise, the performance tests were made using the AAPM Task Group 126 method, and the results were compared with NEMA NU-2018. RESULTS: The sensitivity at the isocenter was 8.87 cps/kBq according to NEMA and 7.60 cps/kBq by using the AAPM Task Group 126. For the spatial resolution, the full width at half maximum (FWHM) and FWTM values were 4.34 mm and 6.78 mm at 1 cm radial offset by NEMA, while AAPM Task Group 126 yielded FWHM and FWTM values of 4.42 mm and 8.14 mm, respectively. In the image quality, NEMA exhibited hot lesions contrast of 40.8, 56.7, 69.9, and 77.3 for 10, 13, 17, and 22 mm spheres, respectively. As a ratio to 25 mm, the "Hot" max standard uptake values by AAPM Task Group 126 were found to be 1, 1.1, 1.37, and 1.68 for 8, 12, 16, and 25 mm lesions, respectively. CONCLUSION: Acceptance tests using NEMA are of high relevance and convenience for the reliability of the results. Alternatively, AAPM Task Group 126 seems convenient and more economical to apply with reliable outcomes for the equivalent tests.

SPECT/CT-based dosimetry of salivary glands and iodine-avid lesions following 131I therapy.

Objective: The purpose was to provide uptake and radiation dose estimates to salivary glands (SG) and pathologic lesions following radioiodine therapy (RIT) of differentiated thyroid cancer patients (DTC). Methods: A group of DTC patients (n = 25) undergoing 131I therapy joined this study with varying amounts of therapeutic activity. Sequential SPECT/CT scans were acquired at 4 ± 2, 24 ± 2, and 168 ± 3 h following administration of 3497-9250 MBq 131I. An earlier experiment with Acrylic glass body phantom (PET Phantom NEMA 2012 / IEC 2008) was conducted for system calibration including scatter, partial volume effect and count loss correction. Dose calculation was made via IDAC-Dose 2.1 code. Results: The absorbed dose to parotid glands was 0.04-0.97 Gy/GBq (median: 0.26 Gy/GBq). The median absorbed dose to submandibular glands was 0.14 Gy/GBq (0.05 to 0.56 Gy/GBq). The absorbed dose to thyroid residues was from 0.55 to 399.5 Gy/GBq (median: 21.8 Gy/GBq), and that to distal lesions ranged from 0.78 to 28.0 Gy/GBq (median: 3.12 Gy/GBq). 41% of the thyroid residues received dose > 80 Gy, 18% between 70-80 Gy, 18% between 40-70 Gy, and 23% has dose < 40 Gy. In contrast, 18% of the metastases exhibited a dose > 80 Gy, 9% between 40-60 Gy, and the dose to the vast majority of lesions (64%) was < 40 Gy. Conclusion: It was inferred that dose estimation after RIT with SPECT/CT is feasible to apply, together with good agreement with published 124I PET/CT dose estimates. A broad and sub-effective dose range was estimated for thyroid residues and distal lesions. Moreover, the current methodology might be useful for establishing a dose-effect relationship and radiation-induced salivary glands damage after RIT.

Simplification of dosimetry in 90Y-radioembolization therapy by dual planar images.

AIM: The purpose was to provide a practical and effective method for performing reliable 90Y dosimetry based on 99mTc-MAA and SPEC/CT. The impact of scatter correction (SC) and attenuation correction (AC) on the injected 90Y activity, lung shunt fraction (LSF) and the delivered dose to lung and liver compartments was investigated within the scope of the study. MATERIAL AND METHODS: Eighteen eligible patients (F: 3, M: 15) were subjected to 90Y therapy. 99mTc-MAA (111-222 MBq) was injected into the targeted liver, followed by whole-body scan (WBS) with peak-window at 140 keV (15% width) and one down-scatter window. SPECT/CT scan was subsequently acquired encompassing lung and liver regions. The LSFs were fashioned from standard WBS LSFwb (St), scatter corrected WBS LSFwb (Sc), only scatter corrected SPECT LSFspect (NoAC-SC) and SPECT/CT with attenuation and scatter correction LSFspect (AC-SC). The absorbed doses that would be delivered to tumor and injected healthy liver were estimated using different calculation modes involving AC-SC (SPECT/CT), NoAC-SC (SPECT), NoAC-NoSC+LSFwb (SC), AC-SC + LSFwb (St), and NoAC-NoSC+LSFwb (St). RESULTS: The average deviations (range) in LSF values between standard LSFwb (St) and those from SPECT/CT (AC-SC), SPECT (NoAC-SC), and LSFwb (SC) were - 50% (- 29/- 71), - 32% (- 8/- 67), and - 45% (- 13/80), respectively. The suggested 90Y activity (GBq/Gy) was decreased within a range of 2-11%, 1-9%, and 2-7% by using LSFspect (AC-SC), LSFspect (NoAC-SC), and LSFwb (SC), respectively. Overall, two-sample t-test yielded no statistically significant difference (p < 0.05) in the absorbed doses to tumor and injected healthy liver between AC-SC (SPECT) and the rest of approaches with/and without AC and SC. However, a statistically significant difference (p < 0.05) was demonstrated in the lung shunt fractions and lung doses due to AC and SC. The LSFs from scatter corrected planar images LSFwb (SC) exhibited well agreement (R2 = 0.92) with SPECT/CT (AC-SC) and there was no statistically significant difference (Pvalue > 0.05) between both methods. CONCLUSION: It was deduced that SPECT/CT with attenuation and scatter correction plays a crucial role in the measurements of lung shunt fraction and dose as well as the total number of 90Y treatments. However, the absorbed dose to tumors and injected healthy liver was minimally affected by AC and SC. Besides, a good agreement was observed between LSF datasets from SPECT/CT versus scatter corrected WBS that can be alternatively and effectively used in 90Y dosimetry.

The Interference of Gamma Rays With Bone Mineral Density Measurements in 177Lu-PSMA and DOTATATE Therapy.

The main purpose was to describe the interference of gamma radiation emitted by 177Lu with simultaneous bone mineral density BMD measures for patients undergoing 177Lu-PSMA and 177Lu DOTATATE therapy. A cohort of 9 patients underwent 177Lu-PSMA therapy were randomly selected to speculate the activity in the abdominopelvic region. So that, SPECT/CT scan at 24 h was used with attenuation and scatter correction. The activities were derived from the delineated ROIs over the abdominopelvic zone showing a range of 34-274 MBq. Next, a water path was placed under spine phantom mimicking L1-L4 vertebrae and followed by consecutive DEXA scans made by Hologic 4500 W and GE-Lunar DPX-NT systems. Five scans were performed without/and with different Lu-177 activities 37, 185, 370 and 555 MBq under the same geometric conditions. The obtained BMD readings of L1-L4 by the Hologic device were 1.027, 1.024, 1.021, 1.013, and 1.006 g/cm2 with presence of 0, 37, 185, 370, and 555 MBq 177Lu activity, respectively. Whereas, in Lunar device, it was found as higher as 1.163, 1.121, 1.09, 1.072, and 1.043, respectively. There was no statistically significant difference between both devices (pvalue ≥ 0.05). The fluctuation ranges in the L1-L4 BMD readings at the presence of 37-555 MBq were 0.3%-2%, and 3.6%-10.3% for Hologic and Lunar systems, respectively. It was emphasized that gamma radiation emitted by 177Lu relatively influence DEXA scans and the yielded BMD measures. Postponing DEXA scans as early as 8 d after 177Lu-PMSA and 11 d after 177Lu-DOTATATE therapies is recommended to avoid the erroneous contribution of gamma radiation and provide precise bone assessment.

Quantitative improvement of lymph nodes visualization of breast cancer using 99mTc-nanocolloid SPECT/CT and updated reconstruction algorithm.

This study aimed to evaluate the impact of attenuation and scatter correction on the contrast to noise ratio values of SPECT and SPECT/CT images in sentinel lymph nodes scintigraphy. In addition, the effect of using an iterative reconstruction algorithm with variable iterations number and fixed subsets was also investigated. 35 patients with a total of 44 lymph nodes were recruited in the current study. SPECT/CT scans were performed 3-4 h following peri-tumoral 99mTc-nanocolloid injection (≈1 mCi) at four points. Two image types were generated including SPECT with attenuation and scatter correction (AC-SC) and SPECT without any correction (NoAC-NoSC). The acquired projections were repeatedly reconstructed with eight subsets and 10, 20, 30 and 40 iterations. Afterwards, the calculated contrast to noise ratio values were used to investigate the effect of number of iteration and to compare the image quality of SPECT/CT and SPECT only. The mean contrast to noise (CNR) values of SPECT/CT scans were found to be 19,737, 26,418, 34,282 and 31,187 at 10, 20, 30 and 40 iterations, respectively. Whereas, the mean CNR values in SPECT (NoAC-NoSC) were as low as 8506, 10,582, 13,791 and 12,143 at 10, 20, 30 and 40 iterations, respectively. The CNR values of both SPECT and SPECT/CT improved with increasing number of iterations up to 30 iterations and then slightly decreased after 30-40 iterations. Likewise, no significant difference was found between 10 and 20 iterations (Pvalue = 0.06) in SPECT/CT, while a statistically significant difference was observed between 10 iterations and both 30 and 40 iterations (Pvalue < 0.05). It is concluded that the attenuation and scatter correction in SPECT/CT optimized the CNR values up to threefold compared to SPECT alone. Thus, a considerable improvement in the CNR values and the image quality can be obtained by increasing the iterations number to peak of 30 iterations.

The impact of different computational assumptions in 131 I dosimetry for hyperthyroidism therapy.

PURPOSE: The goal of the current study was to investigate the impact of different computational models on 131 I dosimetry prior to hyperthyroidism therapy. It was also aimed to highlight an accurate and cost-effective method for routine dosimetry of graves and toxic adenoma patients. METHODS: A cohort of 45 patients was recruited in the current study with Graves (n = 30) and Toxic Adenoma (n = 15) diseases. The eligibility criterion was determined using the patients' blood test, 99m Tc- pertechnetate scintigraphy, and ultrasound scan. A properly calibrated thyroid probe equipped with sodium iodide crystal [NaI(Tl)] was used to obtain the uptake measurements at 2, 24, 48, 72, and 96 h following administration of 0.27-0.73 MBq 131 I tracer. The absorbed radiation dose of the thyroid gland/nodule was calculated by three different methods. The calculation models were based on the time-integrated activity (recommended by MIRD), effective half-life (recommended by EANM), and ellipsoidal-shape assumption. RESULTS: The mean effective half-life was 138 ± 41 h and 110 ± 48 h in Graves and Toxic Adenoma patients, respectively. The mean residence time was 125 ± 5 h in Graves patients, while it was 93 ± 55 h in Toxic Adenoma. The amount of 131 I activity required to deliver 200 Gy to the thyroid gland in Graves patients was calculated as 436 ± 381 MBq, 426 ± 370 MBq, and 488 ± 455 MBq according to MIRD, EANM, and ellipsoidal-shape model, respectively. However, the activity required to impart 300 Gy in the toxic nodules was computed as 622 ± 332 MBq by MIRD, 907 ± 588 MBq by EANM, and 1060 ± 639 MBq by the ellipsoidal-shape model. Overall, no significant difference was found between the MIRD and both of the EANM and ellipsoidal-shape models in the Graves patients (R2  = 0.99, P > 0.05). In contrast, less agreement (R2  = 0.86) was shown between EANM and MIRD in Toxic Adenoma patients with no statistically significant difference (P > 0.05), while the difference was significant (Pvalue  < 0.05) between the MIRD and the ellipsoidal-shape model with moderate association (R2  = 0.66). CONCLUSION: It was deduced that the effective half-life-based model (EANM model) is a successful and affordable method for performing dosimetry in Graves patients. While, unit density sphere model sounds the most appropriate approach to be used in Toxic Adenoma dosimetry. However, using the ellipsoidal-shape assumption in the thyroid gland/or nodule dose calculation leads to redundantly larger activity administration.

Thyroid uptake test with portable device (COTI) after 131I tracer administration: proof of concept.

COTI (collar therapy indicator) has been recently introduced for the detection of gamma rays with emphasis on thyroid investigations. The aim of this study was to test the feasibility of a prototype version of COTI including activity detectors with low sensitivity in performing thyroid uptake measurements for a large group of patients. Consequently, thyroid uptake tests were carried out for a total of 89 patients (22 males and 67 females; age: 44 ± 13 years) with thyroid cancer (n = 74), hyperthyroidism (n = 16) at 2 and 24 h after administration of 0.44-2 MBq of 131I. Eight individuals among the thyroid cancer patients were monitored up to 96 h after administration. The COTI device was equipped with two CsI (Tl) detectors, known as LoHi type, sensitive to activity ranges from 0.02 to 30 MBq of 131I. The uptake values from COTI were compared with those measured with a standard probe. It was found that the mean uptake of thyroid activity in thyroid cancer patients was 2.1 ± 1.3% at 2 h when measured with the standard probe, while it was 2.2 ± 1.2% when measured with COTI. In addition, the average uptake at 24 h after administration was 2.5 ± 3.2% and 3.2 ± 3.8% measured with COTI and the standard probe, respectively. A strong correlation was found at 24 h between the results obtained with COTI and the standard probe, while a weaker correlation was seen at 2 h. Overall, there was no significant difference between the results obtained with the standard probe and those obtained with COTI at both 2 and 24 h (Pvalue ≥ 0.05). Besides, 85% of the uptake values measured with COTI were less than those measured with the standard probe at the 24 h after administration. The average uptake value was 0.9 ± 0.8% after 96 h by COTI, and 1.4 ± 1.3% by the standard probe. Pertaining to the hyperthyroidism patients, COTI showed mean uptake values of 20 ± 16% and 23 ± 18% at 2 and 24 h, respectively. In contrast, the standard probe suggested higher mean uptake values of 26 ± 18% and 30 ± 22%, respectively. It is concluded that the prototype of COTI used in the present study has been proved to be a feasible and promising tool in thyroid investigations. It is noted, however, that the next COTI generation should include detectors equipped with collimator and energy discrimination.

Comparison of PERCIST and RECIST criteria for evaluation of therapy response after yttrium-90 microsphere therapy in patients with hepatocellular carcinoma and those with metastatic colorectal carcinoma.

OBJECTIVE: Yttrium-90 (Y) microsphere therapy has been increasingly used to treat hepatocellular carcinoma (HCC) and liver metastasis of colorectal cancer (mCRC). This study aims to compare two different criterias used for therapy response evaluation following Y therapy within the same group of patients. PATIENTS AND METHODS: A total of 21 patients with HCC and 19 patients with mCRC were included in this study, with 36 and 42 liver lesions, respectively. The lesions were evaluated before and after therapy by CT or MRI and fluorine-18 fluorodeoxyglucose (F-FDG) PET/CT. Several metabolic parameters were analyzed including maximum and mean standardized uptake values, peak standardized uptake value, metabolic tumor volume (MTV), and total lesion glycolysis. Tumor volume was determined using CT or MRI images for all lesions, and the applied activity was estimated to deliver 120±20 Gy for the treated lobe. Six weeks after Y microsphere therapy, F-FDG PET/CT scan was performed to evaluate tumor response using PERCIST and RECIST criteria. Overall survival was calculated using Kaplan-Meier method. RESULTS: A total of 78 liver lesions were treated without any major complication. The mean tumor volumes of HCC lesions calculated by CT or MRI before and after therapy were 84.38 and 86.62 cm, respectively. The average MTV of these lesions on PET images was calculated as 68.142 mm before therapy and 56.945 mm after treatment. In patients with mCRC, the mean tumor volume was 52.32 cm before therapy and 54.52 cm after therapy. The average MTV was calculated as 41.720 mm before and 44.967 mm after therapy for the same patient group. Response Evaluation Criteria In Solid Tumors (RECIST) and PET Response Criteria In Solid Tumors incompatibility was seen in seven of 36 lesions in HCC-diagnosed patients and seven of 42 lesions in patients with mCRC. The mean overall survival was calculated as 13.09 months in patients with HCC and 10.6 months in patients with mCRC. CONCLUSION: Y therapy response can be evaluated by both RECIST and European Organization for Research and Treatment of Cancer criteria. However, RECIST and European Organization for Research and Treatment of Cancer incompatibility can be seen. The anatomic methods for evaluating HCC response is relatively more accurate, whereas the metabolic parameters guided by PET/CT scan showed greater importance in response to evaluation of liver mCRC.

Red bone marrow dose estimation using several internal dosimetry models for prospective dosimetry-oriented radioiodine therapy.

The aim of the present study was to review the available models developed for calculating red bone marrow dose in radioiodine therapy using clinical data. The study includes 18 patients (12 females and six males) with metastatic differentiated thyroid cancer. Radioiodine tracer of 73 ± 16 MBq 131I was orally administered, followed by blood sampling (2 ml) and whole-body scans (WBSs) done at several time points (2, 6, 24, 48, 72, and ≥ 96 h). Red bone marrow dose was estimated using the OLINDA/EXM 1.0, IDAC-Dose 2.1, and EANM models, the models developed by Shen and co-workers, Keizer and co-workers and Siegel and co-workers, and Traino and co-workers, as well as the single measurement model (SMM). The results were then compared to the standard reference model Revised Sgouros Model (RSM) reported by Wessels and co-workers. The mean dose deviations of the Traino, Siegel, Shen, Keizer, OLINDA/EXM, EANM, SMM, and IDAC-Dose 2.1 models from the RSM were - 17%, - 24%, 6%, - 29%, - 15%, 40%, 48%, and - 8%, respectively. The statistical analysis demonstrated no significant difference between the results obtained with the RSM and with those obtained with the Shen, Traino, OLINDA/EXM, and IDAC-Dose 2.1 models (t test; pvalue > 0.05). However, a significant difference was found between RSM doses and those obtained with the EANM, SMM, and Keizer models (t test; pvalue < 0.05). The correlation between red marrow dose from the SMM and EANM models was modest (R2 = 0.65), while the crossfire dose calculated with the OLINDA/EXM and IDAC-Dose 2.1 models were in good agreement with each other and with the reference model. The findings obtained indicate that most of the dosimetry models can be used for a reliable dosimetry, and the calculated total body doses can be considered as a reliable non-invasive option for a conservative activity planning. In addition, the excellent performance of the IDAC-Dose 2.1 model will be of particular importance for a practical and accurate dosimetry, with the advantages of allowing for the use of realistic advanced phantoms and updated dose fractions, and of providing information about the blood dose contribution to the red bone marrow.

Indirect assessment of the maximum empirical activity (250 mCi) with respect to dosimetry concepts in radioiodine therapy of metastatic differentiated thyroid cancer.

AIM: The development of reliable dosimetry models promotes the individualized therapy concept toward more success and less complications. This paper evaluates the traditional maximum empirical activity (250 mCi) and the benefit of joining two dosimetry approaches to optimize the therapeutic activity and radioiodine efficacy in metastatic differentiated thyroid cancer. MATERIALS AND METHODS: Nineteen (12 females and seven males) patients with metastatic differentiated thyroid cancer were included in the present study. The mean age of the patients was 46±16 years. The mean height and weight were 1.67±0.11 m and 76±18 kg, respectively. Radioiodine treatment was given by recombinant human thyrotropin stimulation in seven patients, and thyroxine withdrawal was successful for the rest 12 patients. The mean thyroid-stimulating hormone value was 68±34 µIU/ml, and the mean thyroglobulin value was 408±356 ng/ml before therapy. After radiotracer administration, lesion-absorbed dose was calculated in addition to red marrow dose estimation via two different models. RESULTS: Total body and blood residence time was found to be 30±17 and 4.5±1.9 h, respectively. Red marrow absorbed dose was 0.535±0.262 Gy/100 mCi using the model accounts for red marrow dose surrogated by blood, and it was 0.398±0.212 Gy/100 mCi using a modified model with mean deviation of -24% (range: -19 to -31%). Red marrow absorbed dose was found to be 0.50±0.15 Gy/100 mCi in the levothyroxine withdrawal group, whereas it was 0.46±0.2 Gy/100 mCi for the patients who received recombinant human thyrotropin. Mean lesion-absorbed dose was 0.16±0.14 Gy/g/mCi. The speculated dose from 250 mCi iodine-131 was evaluated, as 65% of all lesions (n=27) would receive at least 100 Gy, whereas the percentage of bone lesions that would receive at least 100 Gy was only 55%. CONCLUSION: Upon to this study, red marrow dose varies with type of preparation as that of medication withdrawal cases was slightly higher than exogenous thyroid-stimulating hormone. Involvement of lesion and red marrow dose assessment through dosimetry protocol seems indeed valuable to optimize safe and effective activity compared with the conventional regime with 250 mCi as maximum empirical activity.

Evaluation of PET Scanner Performance in PET/MR and PET/CT Systems: NEMA Tests.

OBJECTIVE: The aim of the present study was to compare the performance of positron emission tomography (PET) component of PET/computed tomography (CT) with new emerging PET/magnetic resonance (MR) of the same vendor. METHODS: According to National Electrical Manufacturers Association NU2-07, five separate experimental tests were performed to evaluate the performance of PET scanner of General Electric GE company; SIGNATM model PET/MR and GE Discovery 710 model PET/CT. The main investigated aspects were spatial resolution, sensitivity, scatter fraction, count rate performance, image quality, count loss and random events correction accuracy. RESULTS: The findings of this study demonstrated superior sensitivity (~ 4 folds) of PET scanner in PET/MR compared to PET/CT system. Image quality test exhibited higher contrast in PET/MR (~ 9%) compared with PET/CT. The scatter fraction of PET/MR was 43.4% at noise equivalent count rate (NECR) peak of 218 kcps and the corresponding activity concentration was 17.7 kBq/cc. Whereas the scatter fraction of PET/CT was found as 39.2% at NECR peak of 72 kcps and activity concentration of 24.3 kBq/cc. The percentage error of the random event correction accuracy was 3.4% and 3.1% in PET/MR and PET/CT, respectively. CONCLUSION: It was concluded that PET/MR system is about 4 times more sensitive than PET/CT, and the contrast of hot lesions in PET/MR was ~ 9% higher than PET/CT. These outcomes also emphasize the possibility to achieve excellent clinical PET images with low administered dose and/or a short acquisition time in PET/MR.

Blood clearance and occupational exposure for 177Lu-DOTATATE compared to 177Lu-PSMA radionuclide therapy.

The main target of this work is to examine blood clearance and external exposure for 177Lu-DOTATATE compared with new emerging 177Lu-PSMA therapy. Blood clearance and radiation exposure of 31 patients treated with 5.5 ± 1.1 GBq 177Lu-DOTATATE were compared to those of 23 patients treated with 7.4 GBq 177Lu-PSMA. Dose rates were measured at several distances and time points up to 120 h after treatment. Blood samples were collected conjunctively after infusion. Caregiver's cumulative dose was measured by means of an OSL (optically stimulated luminescence) dosimeter for 4-5 days and medical staff's dose was also estimated using electronic personal dosimeters. Finger dose was determined via ring TLD (Thermoluminescence Dosimeter) for radiopharmacists and nurses. Dose rates due to 177Lu-DOTATATE at a distance of 1 m, 4 h and 6 h after infusion, were 3.0 ± 2.8 and 2 ± 1.9 µSv/(h GBq), respectively, while those due to 177Lu-PSMA were 3.1 ± 0.8 and 2.2 ± 0.9 µSv/(h GBq). Total effective dose of 17 caregivers was 100-200 µSv for 177Lu-DOTATATE therapy. Mean effective doses to nurses and radiopharmacists were 5 and 4 µSv per patient, respectively, while those for physicists and physicians were 2 µSv per patient. For 177Lu-DOTATATE, effective half-life in blood and early elimination phase were 0.31 ± 0.13 and 4.5 ± 1 h, while they were found as 0.4 ± 0.1 and 5 ± 1 h, respectively, for 177Lu-PSMA. The first micturition time following 177Lu-DOTATATE infusion was noted after 36 ± 14 min, while the second and third voiding times were after 74 ± 9 and 128 ± 41 min, respectively. It is concluded that blood clearance and radiation exposure for 177Lu-DOTATATE are very similar to those for 177Lu-PSMA, and both treatment modalities are reasonably reliable for outpatient treatment, since the mean dose rate [2.1 µSv/(h GBq)] decreased below the dose rate that allows release of the patient from the hospital (20 µSv/h) after 6 h at 1 m distance.

Lu-177-PSMA-617 Prostate-Specific Membrane Antigen Inhibitor Therapy in Patients with Castration-Resistant Prostate Cancer: Stability, Bio-distribution and Dosimetry.

OBJECTIVE: The aim of the study was to estimate the radiation-absorbed doses and to study the in vivo and in vitro stability as well as pharmacokinetic characteristics of lutetium-177 (Lu-177) prostate-specific membrane antigen (PSMA)-617. METHODS: For this purpose, 7 patients who underwent Lu-177-PSMA therapy were included into the study. The injected Lu-177-PSMA-617 activity ranged from 3.6 to 7.4 GBq with a mean of 5.2±1.8 GBq. The stability of radiotracer in saline was calculated up to 48 h. The stability was also calculated in blood and urine samples. Post-therapeutic dosimetry was performed based on whole body and single photon emission computed tomography/computed tomography (SPECT/CT) scans on dual-headed SPECT/CT system. RESULTS: The radiochemical yield of Lu-177-PSMA-617 was >99%. It remained stable in saline up to 48 h. Analyses of the blood and urine samples showed a single radioactivity peak even at 24 hours after injection. Half-life of the distribution and elimination phases were calculated to be 0.16±0.09 and 10.8±2.5 hours, respectively. The mean excretion rate was 56.5±8.8% ranging from 41.5% to 65.4% at 24 h. Highest radiation estimated doses were calculated for parotid glands and kidneys (1.90±1.19 and 0.82±0.25 Gy/GBq respectively). Radiation dose given to the bone marrow was significantly lower than those of kidney and parotid glands (p<0.05) (0.030±0.008 Gy/GBq). CONCLUSION: Lu-177-PSMA-617 is a highly stable compound both in vitro and in vivo. Lu-177-PSMA-617 therapy seems to be a safe method for the treatment of castration-resistant prostate cancer patients. The fractionation regime that enables the longest duration of tumor control and/or survival will have to be developed in further studies.

Evaluation of radiation safety in (177)Lu-PSMA therapy and development of outpatient treatment protocol.

The aim of this study is to investigate the outpatient treatment protocol and radiation safety of a new-emerging lutetium-177 ((177)Lu) prostate specific membrane antigen (PSMA) therapy. This work analyzed the dose rate of 23 patients treated with 7400 MBq (177)Lu-PSMA at different distances (0, 0.25, 0.50, 1.0 and 2.0 m) and variable time marks (0, 1, 2, 4, 18, 24, 48 and 120 h) after the termination of infusion. Blood samples were withdrawn from 17 patients within the same group at 3, 10, 20, 40, 60 and 90 min and 2, 3, 24 h after termination of infusion. Seven different patients were asked to collect urine for 24 h and a gamma well counter was used for counting samples. Family members were invited to wear an optically stimulated luminescence dosimeter whenever they were in the proximity of the patients up to 4-5 d. The total dose of the medical team including the radiopharmacist, physicist, physician, nurse, and nuclear medicine technologist was estimated by an electronic personnel dosimeter. The finger dose was determined using a ring thermoluminescent dosimeter for the radiopharmacist and nurse. The mean dose rate at 1 m after 4 h and 6 h was 23 ± 6 µSv h(-1) and 15 ± 4 µSv h(-1) respectively. The mean total dose to 23 caregivers was 202.3 ± 42.7 µSv (range: 120-265 µSv). The radiation dose of the nurse and radiopharmacist was 6 and 4 µSv per patient, respectively, whereas the dose of the physicist and physician was 2 µSv. The effective half life of blood distribution and early elimination was 0.4 ± 0.1 h and 5 ± 1 h, respectively. Seven patients excreted a mean of 45% (range: 32%-65%) from the initial activity in 6 h. Our findings demonstrate that (177)Lu-PSMA is a safe treatment modality to be applied as an outpatient protocol, since the dose rate decreases below the determined threshold of <30 µSv h(-1) after approximately 5 h and degrades to 20 µSv h(-1) after 6 h.

Effects of hemodialysis on iodine-131 biokinetics in thyroid carcinoma patients with end-stage chronic renal failure.

OBJECTIVES: Radioiodine therapy could be challenging in chronic renal failure patients requiring hemodialysis. The aim of this study was to establish the effects of hemodialysis on elimination of radioiodine from the body in thyroid carcinoma patients with end-stage chronic renal failure and to determine its effects on environmental radiation dose. MATERIALS AND METHODS: Three end-stage chronic renal failure patients (four cases) diagnosed with differentiated thyroid carcinoma requiring radioiodine therapy were included in our study. Each patient was given 50-75 mCi (1850-2775 MBq) iodine-131 with 50% dose reduction. Dose rate measurement was performed at the 2nd, 24th, and 48th hour (immediately before and after hemodialysis) after radioiodine administration. The Geiger-Müller probe was held at 1 m distance at the level of the midpoint of the thorax for the dose rate measurement. RESULTS AND CONCLUSION: The effective half-life of iodine-131 for three patients was found to be 44 h. In conclusion, the amount of radioiodine excreted per hemodialysis session was calculated to be 51.25%.

Determining and Managing Fetal Radiation Dose from Diagnostic Radiology Procedures in Turkey.

OBJECTIVE: We intended to calculate approximate fetal doses in pregnant women who underwent diagnostic radiology procedures and to evaluate the safety of their pregnancies. MATERIALS AND METHODS: We contacted hospitals in different cities in Turkey where requests for fetal dose calculation are usually sent. Fetal radiation exposure was calculated for 304 cases in 218 pregnant women with gestational ages ranging from 5 days to 19 weeks, 2 days. FetDose software (ver. 4.0) was used in fetal dose calculations for radiographic and computed tomography (CT) procedures. The body was divided into three zones according to distance from the fetus. The first zone consisted of the head area, the lower extremities below the knee, and the upper extremities; the second consisted of the cervicothoracic region and upper thighs; and the third consisted of the abdominopelvic area. Fetal doses from radiologic procedures between zones were compared using the Kruskal-Wallis test and a Bonferroni-corrected Mann-Whitney U-test. RESULTS: The average fetal doses from radiography and CT in the first zone were 0.05 ± 0.01 mGy and 0.81 ± 0.04 mGy, respectively; 0.21 ± 0.05 mGy and 1.77 ± 0.22 mGy, respectively, in the second zone; and 6.42 ± 0.82 mGy and 22.94 ± 1.28 mGy, respectively, in the third zone (p < 0.001). Our results showed that fetal radiation exposures in our group of pregnant women did not reach the level (50 mGy) that is known to increase risk for congenital anomalies. CONCLUSION: Fetal radiation exposure in the diagnostic radiology procedures in our study did not reach risk levels that might have indicated abortion.

Pre-therapeutic dosimetry of normal organs and tissues of (177)Lu-PSMA-617 prostate-specific membrane antigen (PSMA) inhibitor in patients with castration-resistant prostate cancer.

PURPOSE: (177)Lu-617-prostate-specific membrane antigen (PSMA) ligand seems to be a promising tracer for radionuclide therapy of progressive prostate cancer. However, there are no published data regarding the radiation dose given to the normal tissues. The aim of the present study was to estimate the pretreatment radiation doses in patients who will undergo radiometabolic therapy using a tracer amount of (177)Lu-labeled PSMA ligand. METHODS: The study included seven patients with progressive prostate cancer with a mean age of 63.9 ± 3.9 years. All patients had prior PSMA positron emission tomography (PET) imaging and had intense tracer uptake at the lesions. The injected (177)Lu-PSMA-617 activity ranged from 185 to 210 MBq with a mean of 192.6 ± 11.0 MBq. To evaluate bone marrow absorbed dose 2-cc blood samples were withdrawn in short variable times (3, 15, 30, 60, and 180 min and 24, 48, and 120 h) after injection. Whole-body images were obtained at 4, 24, 48, and 120 h post-injection (p.i.). The geometric mean of anterior and posterior counts was determined through region of interest (ROI) analysis. Attenuation correction was applied using PSMA PET/CT images. The OLINDA/EXM dosimetry program was used for curve fitting, residence time calculation, and absorbed dose calculations. RESULTS: The calculated radiation-absorbed doses for each organ showed substantial variation. The highest radiation estimated doses were calculated for parotid glands and kidneys. Calculated radiation-absorbed doses per megabecquerel were 1.17 ± 0.31 mGy for parotid glands and 0.88 ± 0.40 mGy for kidneys. The radiation dose given to the bone marrow was significantly lower than those of kidney and parotid glands (p < 0.05). The calculated radiation dose to bone marrow was 0.03 ± 0.01 mGy/MBq. CONCLUSION: Our first results suggested that (177)Lu-PSMA-617 therapy seems to be a safe method. The dose-limiting organ seems to be the parotid glands rather than kidneys and bone marrow. The lesion radiation doses are within acceptable ranges; however, there is a substantial individual variance so patient dosimetry seems to be mandatory.