Patient-Specific Duodenal Hydrogel Spacer as a Dosimetric Buffer for Proton Therapy for Locally Advanced Pancreatic Cancer
D Han1*, H Hooshangnejad 2, J Jatczak3, W Yao4, J Xu5, K Ding6, (1) University of Maryland, Baltimore, MD, (2) Johns Hopkins university, Baltimore, MD, (3) University Of Maryland, (4) University of Maryland School of Medicine, Baltimore, MD, (5) University of Maryland, Baltimore, MD, (6) Johns Hopkins University, Baltimore, MD
Presentations
PO-GePV-T-175 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
ePoster Forums
Purpose: To demonstrate the potential dosimetric benefit of placing a hydrogel spacer for mitigating the toxicity to the duodenum in proton therapy
Methods: A patient diagnosed with locally advanced pancreas cancer (LAPC) was selected for stereotactic body proton therapy (SBPT). The patient was prescribed with 3300 cGy (RBE) in 5 fractions to the GTV. An initial SBPT plan was created to satisfy the the target coverage and duodenum sparing barely.In contrast to current practice of solely being dependent on the expiricence of the physician, our study is to optimize the location and the volume of the spacer, by using a dose fall-off function (DFF) method, which is defined as the derivative of line spread function of dose profile along the abutment. The 3D information of full-width-half-maximum (FWHM) of DFF, dFWHM determined as the space needed for the dose to duodenum drop to 50% of its maximum value and separation needed. Using an in-house, patient-specific spacer simulation platform, FEMOSSA, we placed virtual spacer for the same patient to achieve separation equal to dFWHM. The pre- and post-placement plan quality was compared for the target coverage, and the sparing of duodenum, small bowel.
Results: The separation needed for duodenum and pancreas for the studied patient is 12 mm averaged, which corresponds to 1 cc injection of hydrogel. Similar target coverage was achieved for pre- and post- placed plans with D95 as 3300 cGy (RBE) and 3269 cGy, respectively. The duodenal D1cc has significantly dropped from 3323 cGy to 2573 cGy with hydrogel placed. The dose to the small bowel decreased from V3300cGy 0.16 cc to 0.06 cc.
Conclusion: The dosimetric benefits of optimized injection of the spacer to mitigate the toxicity has been demonstrated. The spacer not only provides the buffer to spare the duodenum, but the feasibility of dose escalation
Funding Support, Disclosures, and Conflict of Interest: Research funding from NIH R37CA229417
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