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Planning Study of Stomach Sparing by Biodegradable Hydrogel Spacer in Stereotactic Body Radiotherapy for Pancreatic Cancer

Z Feng

Z Feng1*, D Li1 , A Rao2 , L Su2 , J Wong2 , A Narang2 , J Herman3 , K Ding2 , (1) Shandong Normal University, Jinan, Shandong, (2) Johns Hopkins University, Baltimore, Maryland, (3) MD Anderson Cancer Center, Houston, TX,


SU-I-GPD-T-419 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Dosimetric advantages of stomach sparing by increasing physical separation from hydrogel injection, was simulated and evaluated for pancreatic cancer stereotactic body radiotherapy (SBRT).

Methods: CT scans from 7 patients previously treated for pancreatic cancer were analyzed in this study. All patients were treated by SBRT with prescription dose 33 Gy in 5 fractions. Original clinical plans were reviewed and dose parameters were extracted. To simulate pancreas-stomach separation, several new simulated structures including sto-5mm, sto-8mm, and sto-15mm were created by avoiding overlap with corresponding expansion structure of original planning target volume (PTV) with 5 mm, 8 mm and 15 mm. Then simulated post-injection plans were re-optimized within these new structures by the same optimized constraints as original plans. V33, V20, V15 of the stomach, as endpoints, were compared between post-injection plans and their corresponding original plan to evaluate dosimetric advantages of stomach sparing.

Results: The mean V15 and V20 of stomach significantly decreased from 10.04 cc to 4.03 cc and 2.07 cc to 0.34 cc, as the simulated separation increasing from 0 mm (without simulated injection) to 5 mm, 8 mm, and 15 mm respectively. As stomach DVH showed, with simulated hydrogel injection, the volume of low dose region (< 5.0 Gy) did not reduce as significantly as the volume in the high dose region (> 7.5 Gy). Whereas mean V33 values were nearly 0 in all simulation plans. With the increase of simulated separation, V33 of PTV has a little increase and V42.9 did not show significant difference.

Conclusion: As the coverage and homogeneity of PTV were comparable, stomach was significantly spared by simulated injection of hydrogel between stomach and pancreas in stereotactic body radiotherapy (SBRT) for pancreatic cancer.

Funding Support, Disclosures, and Conflict of Interest: This research was partially funded by the National Natural Science Foundation of China (NO.61471226), Natural Science Foundation for Distinguished Young Scholars of Shandong Province (NO. JQ201516).We also thank the supporting of Taishan scholar project of Shandong Province.

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