Positioning accuracy for lung stereotactic body radiotherapy patients determined by on-treatment cone-beam CT imaging.
Stereotactic body radiotherapy for early stage non-small cell lung cancer is an emerging treatment option in the UK. Since relatively few high-dose ablative fractions are delivered to a small target volume, the consequences of a geometric miss are potentially severe. This paper presents the results of treatment delivery set-up data collected using Elekta Synergy (Elekta, Crawley, UK) cone-beam CT imaging for 17 patients immobilised using the Bodyfix system (Medical Intelligence, Schwabmuenchen, Germany). Images were acquired on the linear accelerator at initial patient treatment set-up, following any position correction adjustments, and post-treatment. These were matched to the localisation CT scan using the Elekta XVI software. In total, 71 fractions were analysed for patient set-up errors. The mean vector error at initial set-up was calculated as 5.3 ± 2.7 mm, which was significantly reduced to 1.4 ± 0.7 mm following image guided correction. Post-treatment the corresponding value was 2.1 ± 1.2 mm. The use of the Bodyfix abdominal compression plate on 5 patients to reduce the range of tumour excursion during respiration produced mean longitudinal set-up corrections of -4.4 ± 4.5 mm compared with -0.7 ± 2.6 mm without compression for the remaining 12 patients. The use of abdominal compression led to a greater variation in set-up errors and a shift in the mean value.
Regional Medical Physics Department, The James Cook University Hospital, Middlesbrough, UK. neil.richmond@stees.nhs.uk
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Richmond
K E
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Pilling
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C
Peedell
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Shakespeare
C P
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Walker
D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000601:surgery*; D054893:Cone-Beam Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000601:surgery*; D056888:Patient Positioning / Q000592:standards*; D016634:Radiosurgery / Q000379:methods*