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Gareth Price



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    MA23 - Early Stage Lung Cancer: Present and Future (ID 926)

    • Event: WCLC 2018
    • Type: Mini Oral Abstract Session
    • Track: Treatment of Early Stage/Localized Disease
    • Presentations: 1
    • Moderators:
    • Coordinates: 9/26/2018, 10:30 - 12:00, Room 105
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      MA23.06 - Small Residual Setup Errors After Image-Guided Radiotherapy Affect Heart Dose and Are Linked to Overall Survival (ID 13785)

      11:05 - 11:10  |  Author(s): Gareth Price

      • Abstract
      • Presentation
      • Slides

      Background

      There is limited evidence of the effect of radiotherapy image guidance on survival. This work investigates the relationship between small residual set-up errors following IGRT and overall survival in lung cancer patients (mostly with significant comorbidities), and explores which anatomy may be responsible for observed differences.

      a9ded1e5ce5d75814730bb4caaf49419 Method

      Residual setup errors of 546 NSCLC patients treated with an off-line 5mm action threshold correction protocol for bony anatomy were summarized per patient as the mean and standard deviation for each axis, as well as the vector magnitude in a direction from tumour towards the heart, and included in multivariate Cox regression. Delivered dose distributions including residual setup errors were estimated and the difference between the delivered and planned dose was compared for patients who did/did not survive longer than 1 year. Permutation testing (n=1000) assessed significance.

      4c3880bb027f159e801041b1021e88e8 Result

      Residual setup errors were not correlated with any pre-treatment clinical variable. Patients with a residual shift towards the heart (mean ~2 mm, max 5mm) have significantly worse overall survival (hazard ratio 1.310, p = 0.001). The average dose in the heart region changes linearly with the residual shift magnitude towards the heart (~0.8Gy/mm). A higher delivered dose than planned in a region at the heart base (Figure 1, arrow) is associated with poorer survival in multivariate analysis (hazard ratio 1.214/Gy, p<0.001).

      figure1.png

      8eea62084ca7e541d918e823422bd82e Conclusion

      Small residual shifts after IGRT are strongly associated with overall survival in NSCLC patients, with shifts of the high dose region towards the heart leading to worse survival. The most likely cause of shorter survival is a corresponding increase in dose to the heart base. This analysis provides direct evidence of the importance of accurate patient positioning and highlights the significance of the heart base as a dose sensitive organ in thoracic radiotherapy patients with early effects on survival.

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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
    • Track:
    • Presentations: 1
    • Moderators:
    • Coordinates: 9/25/2018, 16:45 - 18:00, Exhibit Hall
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      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): Gareth Price

      • Abstract
      • Slides

      Background

      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.

      fig.png

      8eea62084ca7e541d918e823422bd82e Conclusion

      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.

      [1] Johnson et al. Radiotherapy & Oncology. 2018. Volume 127:S170-1
      [2] Wang et al. J Clin Oncol. 2017. 35(13):1387-94.

      6f8b794f3246b0c1e1780bb4d4d5dc53

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