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Investigation of Inter-Fraction Organ Motions for Patients with Pancreatic Cancer

A Amoush

A Amoush1*, P Xia2, M Abdel-Wahab3, (1) Cleveland Clinic Foundation, Cleveland, OH, (2) The Cleveland Clinic Foundation, Cleveland, OH, (3) Cleveland Clinic, Cleveland, OH

SU-E-J-131 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

To investigate the inter-fractional pancreatic and right kidney motions for patients with pancreatic tumors using daily KV-CBCTs, acquired prior to each treatment.
Five patients with pancreatic adenocarcinoma, who had the stent placements and received IMRT with daily KV-CBCT, were selected for this study. Five weekly CBCTs were input to the Pinnacle treatment planning system and aligned with the planning CT (pCT) with the three different registration methods to investigate inter-fractional organ motions. For each patient, a triple imaging registration was performed, (a) bone-based registration; (2) right-kidney based registration; (3) marker-based registration; Subtracting shifts of the latter two registrations from the bone registration, we obtained the inter-fraction motions for the pancreas and the right kidney. The CTV contours on the CBCTs were transferred from the pCT by using a point-based registration. The right kidney contours on the CBCTs were manually defined. Subsequently, IMRT plans were applied to these CBCTs with the iso-center shifted according to the different registration methods. Dose calculations on the CBCT were set to a density of 1 g/cc. The CTV receiving 95% of the prescription dose (V95%) and the mean dose to the right kidney were evaluated.
A total of 25 CBCT images were analyzed. The average kidney-motion was 3.58±0.43 mm, 2.08±0.36 mm, and 5.94±0.87 mm in the lateral, vertical and longitudinal directions, respectively. The CTV motion was 5.09±0.31 mm, 2.75±0.17 mm, and 7.80±0.92 mm, respectively. V95% of the CTV was 95.65±5.46 %, and 94±11.47 % for the bone-based registration and marker-based registrations, respectively. The mean dose of the right kidney was 6.16±1.87 Gy and 7.48±2.96 Gy, respectively.
The CTV V95% is comparable between bone-registration and marker-based registration and the mean dose to the right kidney is well below the tolerance. Update results from more patients and more daily CBCTs will be reported.

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