Current treatment options for patients with unresectable locally advanced pancreatic cancer (LAPC) include chemotherapy alone or followed by chemoradiation or stereotactic body radiotherapy. However, the prognosis for these patients remains poor, with a median overall survival <12 months. Therefore, novel treatment options are needed. Currently, there is no brachytherapy device approved for pancreatic cancer treatment. Hereby, we present the protocol of a prospective, multicenter, interventional, open-label, single-arm pilot study (OncoPac-1, Clinicaltrial.gov-NCT03076216) aiming to determine the safety and efficacy of Phosphorus-32 when implanted directly into pancreatic tumors using EUS guidance, for patients with unresectable LAPC undergoing chemotherapy (gemcitabine ± nab-paclitaxel).