Program Information
Assess Tumor Intrafraction Motion and Dose Variation by Using Intrafraction KV Projection Streaming
J Liang*, J Zhou , D Zhou , A Qin , D Yan , Beaumont Health System, Royal Oak, MI
Presentations
SU-E-601-2 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: 601
Purpose: Using intrafraction KV imaging to track real-time tumor motion and treatment dose variation.
Methods: Real-time projection images are acquired by Elekta-XVI5 during the treatment delivery and simultaneously transferred to a client computer. Diaphragm at KV image is used as surrogate to predict tumor position. Prior to treatment, diaphragm templates on 2D projection images are created using pre-treatment 4DCT. On treatment day, from pre-treatment KV images, diaphragm positions are detected on 2D projections while tumor positions are obtained from 10 phase reconstructed CBCT. A daily tumor-diaphragm motion correlation model is created. Diaphragm motion is converted into tumor motion and serves as reference. During VMAT delivery, diaphragm positions are detected at each intrafraction projection and subsequently converted into tumor positions. The tumor motion is compared with the daily reference for online correction if necessary. The 4D dose constructed using the pre-treament 4D-CBCT and the intrafraction 4D-CBCT will be compared to evaluate the intrafraction variation. To date, intrafraction tumor motion of 2 hypolung treatments (4 fractions/treatment) has been monitored using our intrafraction motion tracking system.
Results: Diaphragm position detecting took about 70-90 milliseconds per projection, well within the image acquisition interval of 182 milliseconds. Difference of diaphragm position between auto-tracking and manual-tracking were within 1 pixel for 84.2% and 78.1% of projections for KV-only and KV-MV scans respectively. The largest uncertainties were mostly located at the KV-source angles of 70°-110° and 250°-290° where the projections of the right and left lungs overlapped. A tumor baseline shift of -0.2±1.3mm was observed. The target dose D99 constructed using the intrafraction 4D CBCT was reduced up to 1.7% relative to the dose constructed using the pretreatment 4D CBCT.
Conclusion: Real-time tumor position could be tracked in given time interval with high accuracy. Target dose coverage could be improved if necessary online correction is performed.
Funding Support, Disclosures, and Conflict of Interest: Partially Supported by Elekta Research Grant
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