This is a feasibility study in which patients with pancreatic cancer are treated with intratumoral holmium microsphere injections.

Inclusion Criteria:

1. Female or male aged 18 years and over.

2. Diagnosis of primary (borderline) resectable pancreatic cancer by Dutch Pancreatic Cancer Group (DPCG) guidelines:

   i. 1o-90o contact between tumor and the superior mesenteric artery, celiac axis or common hepatic artery. Or; ii. 90o-270o contact between tumor and superior mesenteric vein or portal vein, without occlusion.

   iii. The discussion on resectability has to be made in consensus at multidisciplinary meetings/discussions and may overrule the above criteria (i, ii).

3. Patient is deemed eligible for surgical resection of the pancreatic cancer, however, during open surgery a more advanced disease than initially anticipated is found and resection is no longer feasible.

4. Life expectancy of 12 weeks or longer.

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

6. One or more measurable lesions of at least 10 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. Calcifications in the pancreas or tumour that are highly expected to obstruct the needle tract
3. Any unresolved toxicity greater than National Cancer Institute (NCI), Common Terminology Criteria for Adverse Events (CTCAE version 4.0) grade 2 from previous anti-cancer therapy.
4. Leukocytes < 4.0 109/l and/or platelet count < 100 109/l.
5. 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.
6. Patient is deemed ineligible for implantation of 166Ho by an expert panel (surgeon, nuclear medicine physician and researcher) due to tumour anatomy or nearby structures.
7. Pregnancy or breast feeding (women of child-bearing potential).
8. Patients suffering from psychic disorders that make a comprehensive judgement impossible, such as psychosis, hallucinations and/or depression.
9. Patients who are declared incompetent.