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Hydrogel Separation for Rectum Sparing by Knowledge-Based Planning in Cervical Cancer

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C Tao

C Tao1*, C Ma1 , T Liu1 , J Lu1 , (1) Shandong Cancer Hospital Affiliated to Shandong University, Jinan, Shandong,


SU-I-GPD-T-328 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: By simulating 5 mm hydrogel injection between rectum and planning target volume (PTV) for cervical cancer patients, dosimetric effects were compared and evaluated between without-gel plans and with-gel plans generated by knowledge-based DVH predicting model (Rapidplan).

Methods: 5 clinical patients with cervical cancer were enrolled in this study. Based on primary computed tomography (CT) datasets, without-gel plans were created by knowledge-based planning with the prescription dose of 50.4 Gy/28 fraction. The hydrogel injection process was simulated by created a 5 mm separation structure (CT value fixed to 0) between rectum and PTV. And the rectum was deformed by avoiding gel and ossa coccyges. By the same knowledge-based model, with-gel plans were generated based on these simulated image sets. The dosimetric effects were evaluated by comparing the with-gel plans with their corresponding without-gel plans. Furthermore, the correlation analysis between dose/volume parameter difference (without-gel plan and with-gel plan) and the overlap volume (rectum and 5 mm expansion of PTV) were also evaluated in this study.

Results: The PTV coverage was comparable between without-gel plans (V95 = 99.19%) and with-gel plans (V95 = 99.33%). For rectum, the with-gel plans reduced dose/volume parameters (V40 = 10.41%, V50 = 0.00%, Dmax = 48.9 Gy) compared with the without-gel plans (V40 = 15.38%, V50 = 0.36%, Dmax = 51.96 Gy) with significant differences (p = 0.01, 0.08 and 0.02 for V40, V50 and Dmax, respectively). In addition, R2 of linear fitting between Dmax differences and overlap volume were 0.853, compared with that of V30, V40 and V50 (R2 = 0.244, 0.116, and 0.389, respectively).

Conclusion: Rectum could be significantly spared by injecting hydrogel between rectum and PTV, as PTV coverage were comparable. Difference of Dmax value had a significant correlation with the overlap volume of rectum and 5 mm expansion of PTV.

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