SU‐E‐J‐70: A Study of the Correlation of 3D Surface Matching and KV Imaging for Chestwall IMRT

Purpose: We investigated the accuracy of surface matching compared to kV positioning of 10 post‐mastectomy chestwall patients receiving inverse‐planned, non‐gated IMRT. Methods: During 130 treatment sessions, non‐gated 3D surfaces were captured using AlignRT (v4.5) before and after table translation...

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Bibliographic Details
Published in:Medical Physics 2012-06, Vol.39 (6), p.3668-3668
Main Authors: Al‐Hallaq, H, Gerry, E
Format: Article
Language:English
Subjects:
Computed tomography
Intensity modulated radiation therapy
Medical imaging
Surface treatments
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Summary:Purpose: We investigated the accuracy of surface matching compared to kV positioning of 10 post‐mastectomy chestwall patients receiving inverse‐planned, non‐gated IMRT. Methods: During 130 treatment sessions, non‐gated 3D surfaces were captured using AlignRT (v4.5) before and after table translations as indicated by kV imaging. Surfaces were compared to a reference generated from CT data. Pearson's correlations between ‘indicated’ AlignRT and kV shifts were studied for surface registration of user‐defined regions‐of‐interest (ROIs): the entire surface (‘all’) and the chestwall (‘cw’). In 21% of sessions, two consecutive surfaces of patients in identical positions were used to estimate variability. Finally, the ‘implemented’ shifts detected by AlignRT were calculated and compared to the absolute table translations. Results: Correlations between ‘indicated’ AlignRT and kV shifts were higher for ‘cw’ than for ‘all': r=0.65 (Anterior‐Posterior), r=0.65 (Superior‐Inferier), r=0.44 (Left‐Right). Correlations exhibited large inter‐patient variability; 60% had r0.8) for ‘implemented’ table shifts; only 2 patients demonstrated r1degree were calculated more often when registering ‘cw’ (22%) than ‘all’ (5%). At the treatment position, residual STDs remained high (3.0–3.6mm). Conclusions: On average, ‘cw’ shifts correlated with kV shifts but exhibited significant inter‐patient variability and larger rotations than ‘all’. Differences between AlignRT and kV were ∼3mm for initial patient positioning. The lack of a one‐to‐one correspondence between surface and kV shifts in any single session must be further investigated before clinical implementation.
ISSN:0094-2405
2473-4209
DOI:10.1118/1.4734905