A Novel Absorbable Radiopaque Hydrogel Spacer to Separate the Head of the Pancreas and Duodenum in Radiation Therapy for Pancreatic Cancer

Abstract

We assessed the feasibility and theoretical dosimetric advantages of an injectable hydrogel to increase the space between the head of the pancreas (HOP) and duodenum in a human cadaveric model. Using 3 human cadaveric specimens, an absorbable radiopaque hydrogel was injected between the HOP and duodenum by way of open laparotomy in 1 case and endoscopic ultrasound (EUS) guidance in 2 cases. The cadavers were subsequently imaged using computed tomography and dissected for histologic confirmation of hydrogel placement. The duodenal dose reduction and planning target volume (PTV) coverage were characterized using pre- and postspacer injection stereotactic body radiation therapy (SBRT) plans for the 2 cadavers with EUS-guided placement, the delivery method that appeared the most clinically desirable. Modeling studies were performed using 60 SBRT plans consisting of 10 previously treated patients with unresectable pancreatic cancer, each with 6 different HOP-duodenum separation distances. The duodenal volume receiving 15Gy (V15), 20Gy (V20), and 33Gy (V33) was assessed for each iteration. In the 3 cadaveric studies, an average of 0.9cm, 1.1cm, and 0.9cm HOP-duodenum separation was achieved. In the 2 EUS cases, the V20 decreased from 3.86cm3 to 0.36cm3 and 3.75cm3 to 1.08cm3 (treatment constraint <3cm3), and the V15 decreased from 7.07cm3 to 2.02cm3 and 9.12cm3 to 3.91cm3 (treatment constraint <9cm3). The PTV coverage improved or was comparable between the pre- and postinjection studies. Modeling studies demonstrated that a separation of 8mm was sufficient to consistently reduce the V15, V20, and V33 to acceptable clinical constraints. Currently, dose escalation has been limited owing to radiosensitive structures adjacent to the pancreas. We demonstrated the feasibility of hydrogel separation of the HOP and duodenum. Future studies will evaluate the safety and efficacy of this technique with the potential for more effective dose escalation using SBRT or intensity-modulated radiation therapy to improve the outcomes in patients with unresectable pancreatic cancer.