Ankit Watts

Quality control of positron emission tomography radiopharmaceuticals: An institutional experience.

Purpose of the Study: To study quality control parameters of routinely prepared positron emission tomography (PET) radiopharmaceuticals. Materials and Methods: Three PET radiopharmaceuticals fluorine-18 fluorodeoxyglucose (F-18 FDG), N-13 ammonia (N-13 NH3), and Ga-68 DOTATATE (n = 25 each), prepared by standardized protocols were used. The radionuclide purity, radiochemical purity, residual solvents, pH, endotoxins, and sterility of these radiopharmaceuticals were determined. Results: The physical half-life of radionuclide in radiopharmaceuticals, determined by both graphical and formula method, demonstrated purity of radionuclides used. pH of all PET radiopharmaceuticals used was in the range of 5-6.5. No microbial growth was observed in radiopharmaceutical preparations. The residual solvents, chemical impurity, and pyrogens were within the permissible limits. Conclusions: All three PET radiopharmaceuticals were safe for intravenous administration.

18F-Fluorocholine PET/CT Complementing the Role of Dynamic Contrast-Enhanced MRI for Providing Comprehensive Diagnostic Workup in Prostate Cancer Patients With Suspected Relapse Following Radical Prostatectomy

Purpose The aim of this study was to compare the diagnostic performance of 18F-fluorocholine (FCH) PET/CT and dynamic contrast-enhanced MRI (DCE-MRI) of pelvis in restaging prostate cancer (PC) patients with biochemical recurrence (BCR) following radical prostatectomy (RP). Methods Twenty PC patients who had undergone RP and had BCR were recruited in this study. All the patients underwent whole-body FCH PET/CT and DCE-MRI of the pelvis. An overall pattern of recurrent disease was analyzed, and diagnostic accuracy for the detection of pelvic disease recurrence by the 2 modalities was evaluated by taking histopathologic analysis as the criterion standard. The whole-body FCH PET/CT images were also analyzed separately for the presence of any extra lesion(s). Results The initial mean Gleason score was 6.3 ± 1.53 (range, 4–9). The mean prostate-specific antigen levels at the time of relapse were 1.9 ± 2.87 ng/mL (range, 0.24–13.2 ng/mL). MRI findings were positive for primary tumor recurrence in the prostate bed in 6 patients (6/20 [30.0%]), pelvic lymph node metastases in 4 patients (4/20 [20.0%]), and for pelvic skeletal metastases in 2 patients (2/20 [10.0%]), respectively. On the other hand, FCH PET/CT results were positive in the corresponding sites in 7 (7/20 [35.0%]), 9 (9/20 [45.0%]), and 2 patients (2/20 [10.0%]), respectively. 18F-fluorocholine PET/CT and MRI showed comparable results in terms of sensitivity, specificity, and positive and negative predictive values for PC characterization. The whole-body FCH PET/CT was found to be useful in identifying unknown distant metastases in a significant proportion of patients. Conclusions The correlative whole-body FCH PET/CT and pelvic DCE-MRI offer a complementary and comprehensive diagnostic workup for better management of PC patients with BCR following RP.

Radiation exposure to the personnel performing robotic arm-assisted positron emission tomography/computed tomography-guided biopsies

Purpose: The aim of the study was to estimate the radiation burden to personnel performing robotic arm-assisted positron emission tomography/computed tomography (PET/CT)-guided metabolic biopsies and to staff assisting the procedure in a PET/CT facility. Materials and Methods: We estimated the whole-body exposures to physicians and staff based on the dose rate measurement with an ionization chamber-based calibrated survey monitor and pocket dosimeters during the robotic arm-assisted 2-[F-18]-fluoro-2-deoxy-D-glucose PET/CT-guided biopsies from September 2016 to February 2017. In addition, we also noted the time to biopsy after injection and total biopsy time during which the staff was exposed to the radiation. Results: In this prospective study, PET/CT-guided biopsy was performed in 50 patients (males – 36, females – 14) with a mean age of 54 ± 15 years (range17–78 years). Of the 50 biopsy procedures, 18 were lung biopsies, 10 were bone biopsies, and 22 biopsies were from abdomen/pelvic lesions. The mean time taken for the procedure was 26 ± 11 min. The mean time elapsed between injection and procedure was 182 ± 85 min and mean injected activity of 138.38 ± 74 MBq. The mean whole-body exposure per procedure to an interventionist and an assistant was 1.88 ± 0.82 μSv and 1.04 ± 0.75 μSv, respectively. The mean exposure rates at 0-m and 1-m distance from the patient were 30.77 ± 14.61 μSv/h and 2.59 ± 1.49 μSv/h, respectively. Conclusion: We conclude that the interventionist received the highest mean effective dose as compared to the helping staffs. The occupational radiation exposure was found to be within the limits as specified by the regulatory authorities (International Commission on Radiological Protection-103), and PET/CT-guided biopsies were safe from radiation protection point of view.

99mTc-MDM Brain SPECT for the Detection of Recurrent/Remnant Glioma-Comparison With ceMRI and 18F-FLT PET Imaging: Initial Results.

Purpose To evaluate the diagnostic use of an indigenously developed single vial ready to label (with 99mTc) kit preparation of bis-methionine-DTPA (99mTc-MDM) for the detection of recurrent/residual glioma. Materials and Methods We prospectively studied 32 patients (21 male and 11 female subjects aged 43.0±16.0 years) with clinical suspicion of postoperative recurrent/residual glioma. After radical radiotherapy (54.0–60.0 Gy) with or without concurrent temozolomide as indicated, 99mTc-MDM SPECT and ceMRI of the brain was performed in all the patients and 18F-FLT-PET imaging in 16 of 32 patients. Results MDM SPECT and ceMRI findings were concordant in 28 patients (15 positive and 13 negative). The findings were discordant in the remaining 5 patients, with positive ceMRI and negative MDM-SPECT in 2 patients and negative ceMRI and positive MDM-SPECT in 3 patients. 99mTc-MDM-SPECT, 18F-FLT PET, and ceMRI scan findings were positive in 9 of 16 and negative in 5 of 16 patients. In the remaining 2 of 16 patients, both 18F-FLT-PET and 99mTc-MDM-SPECT were positive, but ceMRI was negative. Sensitivity, specificity, PPV, NPV, and DA of 99mTc-MDM-SPECT for diagnosing recurrent/residual glioma were 88.24%, 81.25%, 83.3%, 86.7%, and 84.8%, respectively. Conclusions The diagnostic accuracy of 99mTc-bis-methionine (MDM)–SPECT imaging was comparable with that of ceMRI and 18F-FLT-PET and may be useful in the management of glioma patients in the postsurgical follow-up period. This imaging technique may be of special interest in peripheral hospitals/developing countries lacking access to expensive PET/cyclotron technology. However, comparison with the existing “gold standard” PET tracers, especially with C-11-methionine-PET imaging and histopathological correlation, is warranted in a large cohort of glioma patients through multicentric studies.

68Ga-Pentixafor PET/CT demonstrating higher CXCR4 density in small cell lung carcinoma than in non-small cell variant

An over-expression of chemokine receptor subtype CXCR4 in many human cancers and targeting CXCR4/CXCR12-axis is viewed as a promising approach for developing specific PET imaging probes [1, 2]. Recently, the pre-clinical evaluation and clinical validation of Ga-labeled Pentixafor (a cyclic pentapeptide) for PET imaging of CXCR4 expression have been described [3–5]. We present a MIP image (A) of Ga-Pentixafor PET/CT in a NSCLC patient showing an intense tracer uptake (transaxialB; SUVmax = 8.8) in the right lung, mediastinal/supra-clavicular lymph nodes, brain (C; SUVmax = 2.2) and L4 spine (D; SUVmax = 4.8). FACS analysis from the lung mass demonstrated significant CXCR4 receptor density with maximum fluorescence intensity(MFI) of 120 (E). Interestingly, an intense uptake (MIP-F; transaxial imageH, SUVmax = 13.2) of Ga-Pentixafor as compared to that of F-FDG (MIP-G; axial-I; SUVmax = 8.0) was observed in a SCLC patient. SCLC in terms of high CXCR4 expression is known to behave more aggressively, and the higher uptake (SUVmax = 13.2) of 68Ga-Pentixafor in this patient was associated with significantly higher CXCR4 expression (MFI = 142.0) than in NSCLC (MFI = 120; SUVmax = 8.8) patient. This image highlights that 68Ga-Pentixafor PET/CT provides an accurate in-vivo localization of CXCR4 expression which can be used for disease assessment and patient selection for appropriate CXCR4 inhibitor therapies.

Incremental Value of Cocktail 18f-fdg and 18f-naf Pet/ct Over 18f-fdg Pet/ct Alone for Characterization of Skeletal Metastases in Breast Cancer

Purpose The aim of this study was to evaluate the incremental value of cocktail 18F-FDG/18F-NaF PET/CT over 18F-FDG PET/CT alone for detection of skeletal metastases in breast cancer patients. Methods Seventy patients with locally advanced/recurrent breast cancer were prospectively included. All patients underwent whole-body 18F-FDG PET/CT and cocktail 18F-FDG/18F-NaF PET/CT within a span of 1 week. Both studies were evaluated to detect presence of skeletal/marrow metastases on PET/CT images by 2 nuclear medicine physicians. Clinical and radiological correlation/follow-up was used as criterion standard. Results Of 70 patients, 50 (71.0%) had locally advanced breast cancer, and 20 had recurrent breast cancer. On patient-wise analysis, both cocktail PET/CT and 18F-FDG PET/CT identified skeletal/marrow lesions in 23 (32.8%) of 70 patients. In 8 patients (11.4%), only cocktail PET/CT identified skeletal/marrow lesions, whereas 18F-FDG PET/CT was negative. In the rest of the 39 patients (55.8%), no skeletal/marrow lesion was identified on both scans. Good correlation was noted between cocktail PET/CT and 18F-FDG PET/CT results (r = 0.785, P < 0.0001). Cocktail PET/CT detected lesions in significantly more number of patients than 18F-FDG PET/CT alone (P = 0.007). On lesion-wise analysis, cocktail PET/CT detected more number of lesions in 20 patients as compared with 18F-FDG-PET/CT alone. Both scans detected same number of lesions in the rest of 11 patients with positive findings. A total of 32 additional lesions were identified on cocktail PET/CT imaging as compared with 18F PET/CT alone (P < 0.0001). Conclusions Cocktail 18F-FDG and 18F-NaF PET/CT is superior to 18F-FDG PET/CT alone for the detection of skeletal/marrow metastases in breast cancer. It can be a better alternative to 18F-FDG PET/CT alone in facilities where both tracers are available.

Radiosynthesis of [18F]-fluorobenzoate-doxorubicin Using Acylation Approach

BACKGROUND Previously, we have labeled doxorubicin with [99Tc] and evaluated its potential as a SPECT agent to detect cancer in tumor bearing mice. In this study, we sought to radiolabel doxorubicin with [18F] using acylation method. METHODS A quaternary salt of the precursor pentamethylbenzyl-4-(trimethylammonium trifluoromethanesulfonate) benzoate was synthesized and characterized by 1H-NMR. As a first step, 4-[18F]- fluorobenzoic acid (FBA) was synthesized from precursor. In second step, [18F]-FBA was further converted to its corresponding acyl form to radiolabel doxorubicin via acylation reaction. RESULTS The total reaction time for the synthesis of [18F]-fluorobenzoate-doxorubicin was about 60 minutes. The radiolabeling efficiency of the final product was estimated to be about 59.0% The radiochemical yield for the synthesis of [18F]-FBA and [18F]-fluorobenzoate-doxorubicin were 19.0- 29.0% and 12.0-14.0% respectively. CONCLUSION Radio synthesis of [18F]-fluorobenzoate-doxorubicin by acylation is a convenient method. However, further improvement in the labeling strategy is required to increase the radiolabeling efficiency and radio synthesis yield. Also, the radiolabeled product needs a detailed pre-clinical evaluation.

Utility of dynamic perfusion PET using ¹³N-ammonia in diagnosis of asymptomatic recurrence of fibrosarcoma.

Fibrosarcoma is a rare tumor involving the musculoskeletal system. Anatomic imaging modalities like CT and MRI are useful in characterization and staging of the tumor. FDG PET has variable sensitivity in evaluation of these tumors. Alternative tracers like FLT have been tried. It is a well-known fact that sarcomas are highly vascular. We report the utility of dynamic perfusion PET imaging using N13-ammonia in diagnosing a case of asymptomatic recurrence of fibrosarcoma in a 45-year-old patient. Despite very faint FDG avidity, ammonia perfusion imaging showed hypervascularity and allowed identification of the asymptomatic early recurrence.