This investigator initiated study with a medical device aims to assess the safety and feasibility of percutaneous injected holmium-166 microsphere brachytherapy in patients with irresectable pancreatic cancer.

Objective: To test the feasibility and safety of minimally invasive CT-guided percutaneous holmium-166 microsphere brachytherapy in patients suffering from irresectable pancreatic cancer. Study design: This is a single centre, prospective, safety and feasibility study with a medical device in a maximum of 6 patients.

Study population: Patients diagnosed with pathologically proven pancreatic adenocarcinoma, who are ineligible for exploratory surgery or surgical resection of the tumour after 8 cycles of systemic therapy or less in case of unacceptable toxicity, patient refusal or patients who are ineligible for systematic therapy.

Intervention (if applicable): A radioactive medical device will be implanted by CT-guided percutaneous injection. The medical device in question are beta-minus (β-) and gamma(γ) emitting holmium-166 poly(L-lactic acid) microspheres (166Ho-PLLA-MS, HoMS) in a 0.1% Pluronic or cellulose based suspension.

Main study parameters/endpoints: The main endpoint is to establish the feasibility and safety of CT-guided percutaneous intratumoural implantation of HoMS in irresectable pancreatic adenocarcinoma. Feasibility is established by evaluating the average tumour absorbed dose in Gray (Gy) calculated on SPECT and comparing to the pre-operative planning. Intratumoural microsphere distribution, absorbed tumour dose and non-target absorbed tumour dose are analysed using MRI and CT quantification. Safety is evaluated using the Common Terminology Criteria for Adverse Events (CTCAE v5.0), events deemed 'unlikely', 'probably' or 'definitely' related to the implantation procedure or implanted medical device. As exploratory endpoints, tumour response (RECIST1.1), pain (NRS) and Quality of Life is evaluated. Total follow-up is 16 weeks.

Inclusion Criteria:

1. Female or male aged 18 years and over.

2. Pathologically proven pancreatic adenocarcinoma, also known as pancreatic ductal adenocarcinoma.

3. Patient is deemed ineligible for surgical resection of the pancreatic cancer:

   1. in accordance with consensus at the multidisciplinary meetings/discussions,
   2. and/or the patient refuses to undergo surgical resection out of personal choice

4. Life expectancy of 16 weeks or longer.

5. World Health Organisation (WHO) Performance status 0-1

6. One or more measurable pancreatic tumours of at least 20 mm in the longest diameter by spiral CT or MRI according to the Response Evaluation Criteria in Solid Tumours (RECIST) 1.1 criteria.

7. Negative pregnancy test for women of childbearing potential.

Exclusion Criteria:

1. Radiation therapy within the last 4 weeks before the start of study therapy.
2. Chemotherapy within the last 2 weeks before the start of study therapy.
3. Calcifications in the pancreas or tumour that are highly expected to obstruct the needle tract
4. Any unresolved toxicity ≥ grade 3 from the National Cancer Institute (NCI), Common Terminology Criteria for Adverse Events (CTCAE version 5.0) from previous anti-cancer therapy.
5. Leukocytes < 3.0 10^9/l and/or platelet count < 75 10^9/l.
6. Kidney failure: Creatine > 165 µmol/l and/or eGFR < 60 ml/min/1,73m^2
7. Significant cardiac event (e.g. myocardial infarction, superior vena cava (SVC) syndrome, New York Heart Association (NYHA) classification of heart disease ≥2 within 3 months before entry, or presence of cardiac disease that in the opinion of the Investigator increases the risk of ventricular arrhythmia.
8. Patient is deemed ineligible for implantation of 166Ho by an expert panel (surgeon, nuclear medicine physician, interventional radiologist, radiologist, and researcher) due to tumour anatomy, nearby structures, patient status or a combination.
9. Pregnancy or breast feeding (women of child-bearing potential).
10. Patients suffering from psychic disorders that make a comprehensive judgement impossible, such as psychosis, hallucinations and/or depression.
11. Patients who are declared incompetent.