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Poster ‐ 46: Intra‐fraction tumor position assessment for lung SBRT in patients treated without customized immobilization devices
Author(s) -
Alamri Iqbal,
Faria Sergio,
Gluszko Jessica,
Patrocinio Horacio
Publication year - 2016
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 - 10.1118/1.4961820
Subject(s) - supine position , cone beam computed tomography , nuclear medicine , medicine , dosimetry , radiation therapy , computed tomography , radiology , surgery
Purpose: To assess intra‐fraction positional stability of lung cancer tumours in patients treated by kilo‐voltage cone‐beam computed tomography (CBCT)‐guided stereotactic body radiotherapy (SBRT) without the use of customized immobilization devices. Material and Methods: Twenty‐two patients underwent 4D‐CT in the supine position with the arms in a wing board but without customized immobilization. The PTV was the internal target volume based on maximum intensity projections and a 5mm symmetric setup margin. Treatments were planned using 7–9 static fields or two volumetric modulated arcs. At treatment, the patient position was adjusted using pre‐treatment CBCT. A post‐treatment CBCT was taken immediately after the treatment ended. The 41 CBCT pairs were automatically matched and the transitional shifts between the two CBCTs recorded. The mean values and standard deviations were calculated for these displacements. Results and conclusions: The mean time between CBCTs (treatment time) was 16.5 ± 6 minutes (range: 10 to 34 minutes). In all cases the tumour remained inside the PTV in the post‐treatment CBCT. The mean shifts between pre and post‐treatment CBCTs were −0.7 ± 1.6 mm (range −5.0 to 3.0 mm) vertically, −0.3 ± 1.7 mm (range −4.8 to 3.0 mm) longitudinally, and −0.4 ± 1.5 mm (range −4.0 to 2.0 mm) laterally. Our results suggest little systematic shifting during treatment, and standard deviations that are consistent with another published report for treatments where customized immobilization was used. This result is encouraging for SBRT programs in clinics with limited resources.