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P2.17 - Treatment of Locoregional Disease - NSCLC (Not CME Accredited Session) (ID 966)
- Event: WCLC 2018
- Type: Poster Viewing in the Exhibit Hall
- Presentations: 1
- Coordinates: 9/25/2018, 16:45 - 18:00, Exhibit Hall
P2.17-08 - Heart Motion in Lung Radiotherapy: How Representative Are Delineations Based on 3DCT, Average and Maximum Projection Scans? (ID 13946)
16:45 - 18:00 | Author(s): Ahmed Bedair
Evidence is emerging that the heart is more radiosensitive than previously assumed [1-2]. However, only delineations on the average projection or 3D CT scans are used for treatment planning. Therefore the motion of this organ due to respiration and contraction is not accounted for. In this pilot study, we assessed how representative the delineations based on the 3D CT scan, average (AVG) and maximum intensity projections (MIP) are.a9ded1e5ce5d75814730bb4caaf49419 Method
Both 3D and 4D CT scans for 7 lung cancer patients treated by SABR were used in this study. Median delineations, derived from 3 independent observers following a previously agreed protocol, were calculated on the 3D CT, AVG, MIP and 25% exhale scans.
Delineations on each 4D phase scan (n=8) were created by propagating the median 25% exhale contours using RayStation v5.99. The volume representing the maximum extent of motion was estimated as the union of all 4D phase delineations (U4D). Surface distances from the U4D to 3D, AVG, MIP volumes were calculated. Distances in the most extreme surface points (1cm most superior/inferior, 10% most right/left/anterior/posterior) are reported.4c3880bb027f159e801041b1021e88e8 Result
Figure 1 shows the distances for the most extreme surface points, for all patients and for each delineation. Patterns vary widely among patients. From the three delineations, MIP is the ‘closest’ to the maximum extent of motion, followed by AVG and 3D.
None of the delineations represented the heart’s maximum extent of motion for all patients, the MIP being the ‘most representative’ volume. All delineations would require an expansion to include all motion. Research including dosimetry measurements and inter-observer variability is required to determine the relevance of expanding the original delineations, and the corresponding margin magnitudes.
 Johnson et al. Radiotherapy & Oncology. 2018. Volume 127:S170-16f8b794f3246b0c1e1780bb4d4d5dc53
 Wang et al. J Clin Oncol. 2017. 35(13):1387-94.
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