Abstract # 2119 Image-guided Radiation Therapy (RT) for Rectal Cancer Using Cone Beam CT (CBCT)

Presenter: Lee, Percy

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Maximum changes for any patient in the cohort in the LAT dimensions were 2.54 (superior), 2.6 (middle), and 1.98 cm (inferior), (Figure). In the AP direction, they
were 2.44, 3.77, and 2.53 cm respectively. The mean deformation change in the
LAT and AP directions were 0.71 and 0.94 cm respectively. Distances from the
geometric center for each patient, between paired CT scans were recorded:
maximum distances for the cohort were 2.24 (superior), 3.77 (middle), 2.53 cm
(inferior). The mean was 0.92 cm. The mean percent RV overlap for an individual
patient ranged from 34.8% - 87.2%. Seven of 8 patients had adequate rectal
coverage despite rectal motion and deformation. Adequacy of a plan was defined
as having > 90% RV covered by 50.4 Gy in all CBCT scans. The single patient
with inadequate rectal coverage (81% RV covered by 50.4 Gy) had a very low mean
percent RV overlap (36.4%).

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