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

Publication date: Available online 14 August 2017
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Avani D. Rao, Ziwei Feng, Eun Ji Shin, Jin He, Kevin M. Waters, Stephanie Coquia, Robert DeJong, Lauren M. Rosati, Lin Su, Dengwang Li, Juan Jackson, Stephen Clark, Jeffrey Schultz, Danielle Hutchings, Seong-Hun Kim, Ralph H. Hruban, John Wong, Amol Narang, Joseph M. Herman, Kai Ding
Purpose/Objectives: We assessed the feasibility and theoretical dosimetric advantages of an injectable hydrogel to increase space between the head of the pancreas (HOP) and duodenum in a human cadaveric model.Materials/MethodsUsing three human cadaveric specimens, an absorbable radiopaque hydrogel was injected between the HOP and duodenum via open laparotomy in one case and endoscopic-ultrasound (EUS) guidance in two cases. 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 post-spacer injection stereotactic body radiotherapy (SBRT) plans of the two cadavers with EUS, the delivery method which appears to be most clinically desirable. Modeling studies were performed using 60 SBRT plans consisting of 10 previously treated unresectable pancreatic cancer patients each with 6 different HOP-duodenum separation distances. Duodenal volume receiving 15 Gy (V15), 20 Gy (V20) and 33 Gy (V33) was assessed for each iteration.ResultsIn the three cadaveric studies, an average of 0.9 cm, 1.1 cm, and 0.9 cm HOP-duodenum separation was achieved, respectively. In the two EUS cases, V20 decreased from 3.86 cc→0.36 cc and 3.75 cc→1.08 cc (treatment constraint: <3 cc), and V15 decreased from 7.07 cc→2.02 cc and 9.12 cc→3.91 cc (treatment constraint: <9 cc), respectively. PTV coverage improved or was comparable between the pre- and post-injection studies. Modeling studies demonstrated that separation of 8 mm was sufficient to consistently reduce V15, V20 and V33 to acceptable clinical constraints.ConclusionsCurrently, dose-escalation is limited due 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 radiotherapy to improve outcomes in unresectable pancreatic cancer patients.

Teaser

We demonstrated the feasibility of an endoscopic ultrasound-guided injectable hydrogel separation technique using a cadaveric model to increase the space between the head of the pancreas and duodenum. Using modeling studies, we identified the minimum distance of this separation for optimal sparing of the duodenum, setting the foundation for future clinical trials utilizing this technique to enable dose-escalation with either stereotactic or intensity-modulated radiotherapy for patients with unresectable pancreatic cancer.


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