Premium
SU‐E‐J‐70: A Study of the Correlation of 3D Surface Matching and KV Imaging for Chestwall IMRT
Author(s) -
AlHallaq H,
Gerry E
Publication year - 2012
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4734905
Subject(s) - nuclear medicine , correlation , standard deviation , medicine , mathematics , physics , statistics , geometry
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 r<0.6 in at least 1 direction thereby resulting in ow correlation between 3D Euclidian shift distances (r=0.48). Correlations between ‘cw’ and kV increased (r>0.8) for ‘implemented’ table shifts; only 2 patients demonstrated r<0.6 in any single direction. Comparison of consecutively‐acquired ‘cw’ surfaces controlled for patient movement demonstrated standard deviations (STDs) of: 1.2mm (A‐P), 2.0mm (S‐I), 1.6mm (L‐R). While STDs between ‘implemented’ and kV shifts were on the same order, STDs between ‘indicated’ and kV shifts were twice as large: 2.9mm (A‐P), 3.5mm (S‐I), 4.1mm (L‐R). Rotational differences >1degree 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.