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Two Courses of Stereotactic Body Radiation Therapy for Pancreatic Cancer: Dose Accumulation and Toxicity

Y Cao1*, X Zhu1 , J Li2 , C Yu1 , Y Sun1 , H Zhang1 , Y Liu1 , S Qing1 , (1) Shanghai Changhai Hospital, Shanghai, Shanghai, (2) Guangdong Nongken Central Hospital, Zhanjiang, Guangdong


(Sunday, 7/29/2018) 4:30 PM - 5:00 PM

Room: Exhibit Hall | Forum 7

Purpose: To assess the accumulated dose of two courses of stereotactic body radiation therapy (SBRT) for pancreatic cancer by deformed registration.

Methods: Forty patients received two courses of SBRT for the same region. Due to different doses to target volumes and organs ta risk (OARs) and fractionation schemes, all treatment schedules were recalculated to an Equivalent Dose of 2 Gy per fraction (EQD2). An α/β value of 10 Gy (Gy10) was employed for the tumor dose and acute effects, and the value determined as 3 Gy (Gy3) concerning late effects. The accumulated dose distribution and doses to OARs were calculated using deformed registration with MIM® System (version: 6.6.8). A dose reduction of 25% and 50% was allowed for the interval of 6-12 months and more than 12 months, respectively. No dose reduction was permitted when re-irradiation was done within 6 months after the first radiotherapy.

Results: The median radiation dose of PTV in the first and second SBRT was 49.58 Gy10 and 41.85 Gy10, respectively. The median accumulated Dmax, D1 and V10 of the stomach, duodenum and the bowel were 36.75Gy3, 27.87 Gy3 and 66.41cc; 30.36 Gy3, 22.13 Gy3 and 18.66cc; 35.76 Gy3, 28.06 Gy3 and 119.48cc, respectively. The median accumulated Dmax of the spinal cord was 6.42 Gy3. The median cumulative Dmean and D2/3 of the left and right kidney were 4.62 Gy3 and 3.03 Gy3; 2.67 Gy3 and 2.10 Gy3, respectively. The median cumulative Dmean and D50% of the liver was 4.28 Gy3 and 3.03 Gy3, respectively. No grade 3-4 toxicity occurred.

Conclusion: The cumulative doses with MIM® software to OARs as dose constraints were acceptable and safe, which could be used as a reference in the treatment planning for re-irradiation with SBRT after prior SBRT for pancreatic cancer.


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