Inclusion Criteria:

          1. Written informed consent.

          2. Patients of either gender, aged ≥ 18 years.

          3. Women of childbearing potential (not surgically sterile or less than 2 years
             postmenopausal) must use a medically accepted method of contraception and must agree
             to continue use of this method for the duration of the study and for 6 months after
             the last dose. Acceptable methods of contraception include abstinence, or double
             contraception: steroidal contraceptive (oral, transdermal, implanted, and injected) in
             conjunction with a barrier method (intrauterine device, condom etc.).

          4. Male patients must use a medically accepted method of contraception and must agree to
             continue use of this method for the duration of the study and for 6 months after the
             last activity administration.

          5. Karnofsky performance score ≥ 60.

          6. Life expectancy of at least 6 months.

          7. Histologically confirmed diagnosis of -

               -  unresectable GEP NET (Grade I and Grade II according to WHO classification (2010,
                  Annex 01), functioning and non-functioning).

               -  unresectable "typical lung carcinoid" or "atypical lung carcinoid" are acceptable
                  (with the exception of Large Cell Bronchial Neuroendocrine Neoplasms and Small
                  Cell Lung Cancers) (Caplin 2015).

               -  malignant, unresectable pheochromocytoma or paraganglioma

          8. Documentation of progressive disease based on RECIST v1.1 under prior anti-tumor
             therapy within 6 months of entry in the study (although the progression might have
             occurred more than 6 months before study entry). Patients should not have received
             further anti-tumor therapy once disease progression is documented. The images of this
             evaluation should be available for TGR evaluation.

          9. In countries where sunitinib or everolimus are marketed, patients with GEP NET and
             lung NET will be progressive under this prior anti-tumor treatment for the respective
             indication. Patients not suitable for everolimus/sunitinib therapy according to a
             tumor board decision (or comparable local practice) may also be enrolled into the
             study. Patients having everolimus/sunitinib therapy should have a wash-out phase of ≥
             4 weeks before the first treatment.

         10. Measurable disease based on RECIST v1.1.

         11. Confirmed presence of somatostatin receptors on technically evaluable tumor lesions
             documented by a positive Somatostatin Receptor Scan performed within 6 months prior to
             enrolment in the study.

         12. Calculated GFR ≥ 55 mL/min.

         13. Blood test results as follows:

               -  Leukocytes: ≥ 4*10^9/L

               -  Erythrocytes: ≥ 3.5*12^9/L

               -  Platelets: ≥ 100*10^9/L

               -  Albumin: > 30 g/L

               -  ALT, AST, AP: ≤ 5 times ULN (upper limit of normal)

               -  Bilirubin: ≤ 2 times ULN (2x 1.1 mg/dL)

        Exclusion Criteria:

          1. Known hypersensitivity to 177Lu, to DOTA, to JR11 or to any of the excipients of
             177Lu-OPS201.

          2. Any previous peptide receptor radionuclide therapy (PRRT).

          3. Diagnosis of thymic NET.

          4. Presence of active infection at screening or history of serious infection within the
             previous 6 weeks.

          5. Administration of any other investigational medicinal product within 60 days prior to
             entry.

          6. Prior or planned administration of a therapeutic radiopharmaceutical within 8
             half-lives of the radionuclide including any time during the current study.

          7. Any extensive radiotherapy ≤ 3 months before enrolment.

          8. Chemotherapy ≤ 3 months before enrolment.

          9. Nephrectomy, renal transplant or concomitant nephrotoxic therapy putting the subject
             at high risk of renal toxicity during the study as assessed by the investigator.

         10. Pregnant or breast-feeding women: A pregnancy test will be performed at the start of
             the study for all female patients of childbearing potential (i.e. not surgically
             sterile or up to 2 years postmenopausal).

         11. Any uncontrolled significant medical, psychiatric or surgical condition (active
             infection, unstable angina pectoris, cardiac arrhythmia, poorly controlled
             hypertension, poorly controlled diabetes mellitus [HbA1c ≥9%], uncontrolled congestive
             heart disease, etc.) or laboratory findings that, in the opinion of the investigator,
             might jeopardize the patient's safety or that would limit compliance with the
             objectives and assessments of the study. Note: the patient should be able to tolerate
             high volume load.

         12. Current history of any malignancy other than NET within 5 years of enrolment except
             for fully -resected non-melanoma skin cancer or cervical cancer in situ. Current
             history of malignancy; patients with a secondary tumor in remission of > 5 years can
             be included

         13. Any mental condition rendering the patient unable to understand the nature, scope and
             possible consequences of the study, and/or evidence of an uncooperative attitude.