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  4. Intra-Fractional Tumor Motion During DIBH Pancreas Treatment

Intra-Fractional Tumor Motion During DIBH Pancreas Treatment

W Xiong , X Li , M Reyngold , R Gewanter , J Cuaron , E Yorke , T Li*, Memorial Sloan-Kettering Cancer Center, New York, NY

Presentations

(Sunday, 7/29/2018) 5:05 PM - 6:00 PM

Room: Room 202

Purpose: Deep inspiration breath hold (DIBH) has been widely used for motion management in radiotherapy. Normally it relies on some external surrogate for estimating the internal target motion. In this study, we used the intrafraction motion review (IMR) functionality on TrueBeam to directly track an internal target, and characterized the residual motion during DIBH treatment for pancreatic cancer patients through their full treatment courses.

Methods: Eight patients with pancreas cancer treated with VMAT+DIBH technique in 2017 were selected for this study, each with some radioopaque markers (fiducials, surgical clips,stent) implanted near or inside the target. DIBH technique involved the Varian RPM, where an external marker is placed on the patient’s abdomen, and a 3mm threshold was used. Before each treatment, a CBCT scan under DIBH was acquired for patient setup. During DIBH treatment, IMR images (i.e. in-treatment kV imaging) were taken every 20 or 40-degree gantry rotation, resulting in a total of ~5000 images for all patients. The internal markers were manually identified in the IMR images, and displacements from their positions in the setup CBCT were calculated. The displacements for each patient’s entire treatment course were analyzed to characterize the typical residual internal motion for DIBH technique.

Results: Even though external marker indicated the respiratory motions were within 3mm in DIBH treatment, significant residual internal target motion was observed for some patients. The average residual motion of each patient for the full treatment courses ranged from 2.7 to 7.9mm, with standard deviation ranging from 1.0 to 2.4mm. For all patients, the mean and standard deviation were 5.1 and 2.5mm, respectively.

Conclusion: Internal target motion may differ from external surrogate motion in DIBH treatment. IMR provides a useful tool to directly monitor the internal target motion.

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