Measurement of cone beam CT coincidence with megavoltage isocentre and image sharpness using the QUASAR Penta-Guide phantom.

Abstract:

:For image-guided radiotherapy (IGRT) systems based on cone beam CT (CBCT) integrated into a linear accelerator, the reproducible alignment of imager to x-ray source is critical to the registration of both the x-ray-volumetric image with the megavoltage (MV) beam isocentre and image sharpness. An enhanced method of determining the CBCT to MV isocentre alignment using the QUASAR Penta-Guide phantom was developed which improved both precision and accuracy. This was benchmarked against our existing method which used software and a ball-bearing (BB) phantom provided by Elekta. Additionally, a method of measuring an image sharpness metric (MTF(50)) from the edge response function of a spherical air cavity within the Penta-Guide phantom was developed and its sensitivity was tested by simulating misalignments of the kV imager. Reproducibility testing of the enhanced Penta-Guide method demonstrated a systematic error of <0.2 mm when compared to the BB method with near equivalent random error (s=0.15 mm). The mean MTF(50) for five measurements was 0.278+/-0.004 lp mm(-1) with no applied misalignment. Simulated misalignments exhibited a clear peak in the MTF(50) enabling misalignments greater than 0.4 mm to be detected. The Penta-Guide phantom can be used to precisely measure CBCT-MV coincidence and image sharpness on CBCT-IGRT systems.

journal_name

Phys Med Biol

authors

Sykes JR,Lindsay R,Dean CJ,Brettle DS,Magee DR,Thwaites DI

doi

10.1088/0031-9155/53/19/002

subject

Has Abstract

pub_date

2008-10-07 00:00:00

pages

5275-93

issue

19

eissn

0031-9155

issn

1361-6560

pii

S0031-9155(08)81157-8

journal_volume

53

pub_type

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