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Evaluation of Offline Adaptive Planning Techniques in Image-Guided Brachytherapy of Cervical Cancer

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H Liu

H Liu1*, J Maurer2 , Q Shang3 , B Sintay4 , T Hayes5 , D Wiant6 , (1) Cone Health Cancer Center, Greensboro, NC, (2) Cone Health Cancer Center, Greensboro, NC, (3) ,Greensboro, NC, (4) Cone Health, Summerfield, NC, (5) Cone Health Cancer Center, Greensboro, NC, (6) Cone Health Cancer Center, Greensboro, NC


TU-L-GePD-T-2 (Tuesday, August 1, 2017) 1:15 PM - 1:45 PM Room: Therapy ePoster Lounge

Purpose: Modern 3D image-guided intracavitary brachytherapy is often used in combination with external beam radiotherapy (EBRT) to manage cervical cancer. Intra-fraction motion of critical organs relative to the applicator in the time between the planning CT and dose delivery can cause marked dose deviations between planned and delivered doses. This study examines offline adaptive planning techniques that may reduce intra-fraction uncertainties by shortening the time between CT and treatment delivery.

Methods: Five patients that received EBRT followed by HDR boosts were retrospectively reviewed. A CT scan was obtained for each insertion. Four strategies were simulated: (A): plans based on the current treatment day CT; (B): plans based on the CT from the previous fraction; (C): plans based on the first fraction CT; (D): current plan based on the closet anatomically matched previous CT. These techniques allow plans to be created prior to insertion, and then rapidly compared with the new CT. Equivalent doses in 2 Gy (EQD2) for EBRT and HDR were compared at D90 for the high risk CTV (HD-CTV) and D2cc for the bladder, rectum, sigmoid and bowel.

Results: Compared to Strategy A, D90 deviations for the HD-CTV were -1.0±1.2 Gy, -1.1±2.9 Gy and -0.5±1.5 Gy for Strategies B, C and D, respectively. Some noticeable D2cc changes were found for rectum, which were 0.5±1.8 Gy, 3.4±5.3 Gy and 1.8±3.1 Gy for Strategies B, C and D. No notable variations for bladder, sigmoid and bowel were found. One patient showed doses over our internal guidelines for bladder and rectum (3Gy for bladder, 0.3 Gy for rectum) for Strategy C.

Conclusion: These techniques can shorten time between CT and treatment from hours to minutes, without loss of dosimetric accuracy, greatly reducing the chance of intra-fraction motion.

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