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Real-Time Monitored Liver SBRT: Delivery Efficiency with Respiratory Gating

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S Shen

S Shen*, R Jacob , R Popple , X Wu , R Cardan , E Covington , I Brezovich , University of Alabama at Birmingham, Birmingham, AL


SU-H2-GePD-J(B)-1 (Sunday, July 30, 2017) 3:30 PM - 4:00 PM Room: Joint Imaging-Therapy ePoster Lounge - B

Purpose: Respiratory gating typically increases irradiation times. This study reports on delivery efficiency of real-time monitored liver SBRT using triggered kV images coupled with respiratory gating.

Methods: 10 patients had 3 polymer/carbon fiducial markers implanted near the tumor prior to simulation. Respiratory gating was required because the cranio-caudal fiducial motion, evaluated fluoroscopically prior to simulation, was >5mm with abdominal compression. A 4DCT scan was obtained for planning and the end-expiration gating window was selected to reduce residual target motion <5mm. The fiducials and a 5mm expansion were contoured on the gate-open phases (typically 30%). Prior to treatment, orthogonal kV and CBCT images were acquired. All patients received 15Gy delivered in 3 fractions by 2 VMAT arcs, 10X-FFF. During treatment, a kV image was triggered at the start of each respiratory cycle. The decision to put beam “on-hold” was made by the treatment team when the fiducial excursion was more than 5 mm.

Results: In 60% of sessions, treatment beam was "on-hold" 1-3 times due to abnormal breathing. Treatment was continued after the fiducials returned to their original positions. This beam "on-hold" added extra 63 sec (median, range 16-144 sec) to each session. Within that sessions required beam "on-hold", 17% required re-imaging and re-adjusting patient position, adding 103 (median, range 63-451) sec. Excluding time required for ‘on-hold’ or re-positioning, the median treatment time (beam-1 start to beam-2 finish) was 600 (range 287-855) sec. For planned gated duty cycle of 40%, actual duty cycle was 36.9 (range 31.4-39.5) %. In comparison, treatment time was 120-223 sec for real-time monitored similar liver SBRT using a pneumatic compression belt without respiratory gating.

Conclusion: Real-time monitored Liver SBRT provided high confidence in tumor dose delivery. The extra time required for putting beams "on-hold" or re-positioning was clinically acceptable.

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