Neuroendocrine tumors (NET) are a heterogeneous group of neoplasms, majority of which express somatostatin (SST) receptors. Recently, with the widespread use of positron emission tomography/computed tomography (PET/CT) and development of novel PET tracers like Ga-68 DOTA peptide which specifically bind to somatostatin receptors (SSTR), Ga-68 DOTA peptide PET/CT is used in management of NET.

To study the various indications for which Ga-68 DOTATATE PET/CT scan was performed and the utility of the scans.

Retrospective evaluation of the patients data was performed who underwent Ga-68 DOTATATE PET/CT as part of their diagnostic workup between June 2011 and July 2012. A total of 145 patients aged 1 to 71 years (mean: 37.4 years) were studied during this period.

Ga-68 DOTATATE PET scan was positive in 23/39 patients referred for characterization or diagnosis, in 6/19 patients for localization, in 13/24 patients for detection of unknown NET primary, in 16/17 patients for staging, in 6/7 patients for recurrence assessment, 12/12 patients for response evaluation, 7/18 patients in restaging and in 5/5 differentiated thyroid cancer patients with thyroglobulin elevated but negative iodine scan.

Ga-68 DOTATATE PET/CT is a useful modality in characterization, localization, detection of unknown NET primary, staging, restaging, recurrence and response evaluation to treatment in patients with NET.

Mittal BR, Agrawal K, Shukla J, Bhattacharya A, Singh B, Sood A, Bhansali A. Ga-68 DOTATATE PET/CT in Neuroendocrine Tumors: Initial Experience. J Postgrad Med Edu Res 2013;47(1):1-6.

Neuroendocrine neoplasms express somatostatin receptors, enabling the use of somatostatin analogs for molecular imaging, when labeled with the positron-emitter ⁶⁸Ga for receptor positron emission tomography/computed tomography (PET/CT), and targeted radionuclide therapy, when labeled with beta-emitters, e.g. ⁹⁰Y and ¹⁷⁷Lu.

To investigate if ⁶⁸Ga-DOTATATE PET-derived standardized uptake values (SUV) correlate with the dose delivered to the liver lesions following ¹⁷⁷Lu-DOTATATE radionuclide therapy in patients with neuroendocrine neoplasms.

Twelve adult (8M: 4F; mean age: 55.9 ± 14.5 years; range: 23-78 years) patients with documented neuroendocrine tumor (NET) disease and liver metastases were enrolled in the study. Ten patients were subjected to ⁶⁸Ga-DOTATATE and one patient each underwent ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTANOC diagnostic PET/CT imaging. Subsequently, on the basis of positive PET/CT scan findings for the metastatic NET disease, all these patients were subjected to peptide receptor radionuclide therapy (PRRNT) with ¹⁷⁷Lu-DOTATATE. The reconstructed PET/CT data was used to calculate the SUVs on the identifiable liver lesions. The scintigraphic data acquired (anterior and posterior whole body images) following therapeutic doses of ¹⁷⁷Lu-DOTATATE were subjected to the quantitative analysis (HERMES workstation and OLINDA/EXM software) to calculate the dose delivered to the hepatic lesions.

The initial results of this preliminary study indicate poor correlation between SUV and the tumor dose and the linear regression analysis provided R2 values which explained only a small fraction of the total variance.

The SUVs derived from ⁶⁸Ga-DOTA-peptide PET/CT images should be used with caution for the prediction of tumor dose on ¹⁷⁷Lu-DOTA-peptide therapy as there are large intra- and interpatient variability. Further studies with large numbers of patients are warranted to establish such a correlation between SUV, tumor dose and the response assessment.

Singh B, Prasad V, Schuchardt C, Kulkarni H, Baum RP. Can the Standardized Uptake Values derived from Diagnostic ⁶⁸Ga-DOTATATE PET/CT Imaging Predict the Radiation Dose delivered to the Metastatic Liver NET Lesions on ¹⁷⁷Lu-DOTATATE Peptide Receptor Radionuclide Therapy? J Postgrad Med Edu Res 2013;47(1):7-13.

Jurcic JG. Targeted Alpha-Particle Immunotherapy with Bismuth-213 and Actinium-225 for Acute Myeloid Leukemia. J Postgrad Med Edu Res 2013;47(1): 14-17.

Rösch F. ⁶⁸Ge/⁶⁸Ga Generators and ⁶⁸Ga Radiopharmaceutical Chemistry on Their Way into a New Century. J Postgrad Med Edu Res 2013;47(1):18-25.

Schultz MK, Donahue P, Musgrave NI, Zhernosekov K, Naidoo C, Razbash A, Tworovska I, Dick DW, Watkins GL, Graham MM, Runde W, Clanton JA, Sunderland JJ. An Increasing Role for ⁶⁸Ga PET Imaging: A Perspective on the Availability of Parent ⁶⁸Ge Material for Generator Manufacturing in an Expanding Market. J Postgrad Med Edu Res 2013;47(1):26-30.

Srivastava SC. A Bridge not too Far: Personalized Medicine with the use of Theragnostic Radiopharmaceuticals. J Postgrad Med Edu Res 2013;47(1):31-46.

Kulkarni HR, Baum RP. Molecular Imaging using PET/CT Applying ⁶⁸Ga-Labeled Tracers and Targeted Radionuclide Therapy: Theranostics on the Way to Personalized Medicine. J Postgrad Med Edu Res 2013; 47(1):47-53.

Rana SS, Sharma V, Bhasin DK. Role of Endoscopic Ultrasound in Gastroenteropancreatic Neuroendocrine Tumors and Update on Their Treatment. J Postgrad Med Edu Res 2013;47(1):54-60.

Laroia ST. ⁹⁰Yttrium Microsphere Radioembolization for Liver Malignancies: A Technical Overview. J Postgrad Med Edu Res 2013;47(1):61-64.

Calculating the absorbed dose is important for the determination of risk and therapeutic benefit of internal radiation therapy. Optimal dose estimations require time-consuming and sophisticated methods, which are difficult due to practical reasons. To make dosimetry available for each of the patients, we developed a specific dosimetry procedure used in daily clinical routine.

Dosimetry has been performed according to the MIRD scheme and adapted to the special conditions at our department (which we have called as the Bad Berka Dose protocol, BBDP): Conjugated planar whole-body scintigraphies at 0.5, 3, 24, 48 and 72 hours postinjection are analyzed by regions of interest with ‘HERMES WHOLE-BODY DISPLAY’ and the time-dependent organ and tumor activities are determined with Microsoft EXCEL™. The cumulated activity is calculated using the software ORIGIN PRO 8.1G™ and a mono- or biexponential fit of the time-activity curves. Mean absorbed doses are finally estimated using the software OLINDA EXM™.

We found a compromise between the calculation model and practical conditions. It has ensured dose estimation in daily clinical routine with a reasonable effort and within acceptable time. In consequence, the dosimetry method developed for Bad Berka allows each of our patients to undergo dosimetry after therapy using Lu-177-labeled peptides (peptide receptor radionuclide therapy). Additionally, this approach can be used for any internal radiotherapy using a gamma-emitting radionuclide.

The BBDP is a practicable dosimetric approach, which can be used in daily clinical routine. It not only helps in identifying patients who would benefit most from the treatment, but also those with unfavorable dosimetry. Additionally, the analysis of dosimetric data from peptide receptor radionuclide therapy (PRRNT) could help in predicting possible toxicity.

Schuchardt C, Kulkarni H, Zachert C, Baum RP. Dosimetry in Targeted Radionuclide Therapy: The Bad Berka Dose Protocol—Practical Experience. J Postgrad Med Edu Res 2013;47(1):65-73.

Shukla J, Mittal BR. Ga-68: A Versatile PET Imaging Radionuclide. J Postgrad Med Edu Res 2013;47(1):74-76.