METHODS
404 images of all 8 head and neck and 9 lung patients studied to
find 2D and 3D set-up errors. CTV to PTV margins were obtained
using calculated set-up errors. The plans of the selected head and
neck and lung patients were calculated to investigate dosimetric
effect of the set-up errors.
RESULTS
kV-kV and CBCT detected average set-up errors for head and
neck patients were less than 2 mm. kV-kV and CBCT detected
average set-up errors for lung patients were less than 7 mm.
While there was a statistically differences (p<0.05) for lung patients,
no statistically differences was found for head and neck
cases as compared kV-kV and CBCT image data sets. The calculated
margin using CBCT image data sets was found bigger than
the calculated margin using kV-kV image data sets. The adequate
and clinically accepted margins were calculated for both IGRT
approach. The neglible dosimetric effects were observed for both
data sets.
CONCLUSION
We conclude that the 2D radiographic image of head and neck
radiotherapy patient reduces positioning errors. While 3D registration
of CBCT and planning CT of head and neck cases adds
little improvement comparing with 2D images, 3D CBCT images
of lung radiotherapy patients provided more accurate information
of the set-up errors.
Keywords: Set-up; CBCT; kV-kV
