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British Journal of Radiology (2006) 79, S66-S78
© 2006 British Institute of Radiology
doi: 10.1259/bjr/68255935
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Developments in and experience of kilovoltage X-ray cone beam image-guided radiotherapy

C J Moore, PhD 1 A Amer, PhD 1 T Marchant, PhD 1 J R Sykes, MSc 1 J Davies, DCR(T) 2 J Stratford, DCR(T) 2 C McCarthy, PgDip 2 C MacBain, MD 3 A Henry, MD 3 P Price, MD 3 and P C Williams, PhD 1

1 North Western Medical Physics Department, 2 Radiotherapy Research Facility, 3 Academic Department of Radiation Oncology, Christie Hospital, Manchester M20 4BX, UK


Figure 1
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  		Figure 1. (a) Flex map pairs taken 2 months apart. U and V describe the projection of a centred ball bearing resolved in the directions of the major orthogonal axes of the imaging panel. Deviations are shown in pixels, at a scale of 0.5 mm pixel–1. Flex maps peaking with the two highest offsets (0.0 and 0.7 pixels) were measured on 19 July 2004 and the remaining two were measured on 15 September 2004 (lower right hand key). (b) Isocentre calibration results for a 1 year period. Variation to the threshold level occurred twice (right hand vertical lines) triggering flex map re-evaluation. Mechanical maintenance triggered precautionary flex map re-evaluation on a further two occasions (left hand vertical lines).

 

Figure 2
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  		Figure 2. (a) The result of 0.6° in-plane, image transducer skew on cone beam tomography (CBT). (b) Results after skew correction. Note the improved contrast and fine detail.

 

Figure 3
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  		Figure 3. Bad pixels, based on their variability, on an amorphous silicon imaging panel.(a) 7000 entries with standard deviation>3 on 1 day. (b) 2000 entries with standard deviation>3 over 5 days.

 

Figure 4
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  		Figure 4. (a) Mean dark field (offset image) computed from 50 sample frames for a gadolinium oxysulphide aSi imaging panel. The axes indicate that the panel can provide up to 1000x1000 pixels per image frame. (b) Mean flood field (gain image) computed from 50 sample frames for a gadolinium oxysulphide aSi imaging panel and high exposure.

 

Figure 5
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  		Figure 5. (a) Radiotherapy planning (RTP)-CT scan, 5 mm slice thickness. (b) Cone beam tomography (CBT) using 383 image profiles, 1 mm slice thickness. The reconstruction is consistent with the theoretical minimum number required for exact reconstruction. (c) CBT using 148 image profiles, 1 mm slice thickness. (d) CBT using 77 image profiles, 1 mm slice thickness. Note the profile aliasing crossing the CBT axial.

 

Figure 6
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  		Figure 6. (a) Radiotherapy planning (RTP)-CT images, 5 mm thick should be compared with (b) the equivalent cone beam tomography (CBT) images, 5 mm equivalent slice thickness by processing (c) the raw CBT data, 1 mm thick gathered at treatment time. In this example, note the changes in rectal and bladder fill.

 

Figure 7
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  		Figure 7. Zonal cone beam tomography(CBT) of a bladder patient reduces scatter from tissues outside the target zone, thus improving target contrast whilst simultaneously preserving edge structures for setup and reducing patient dose. (a) CBT coronal section showing improved target zone contrast (arrow). Note the preserved soft tissue detail above and below. (b) 1 mm axial image detail within the target zone. (c) 1 mm axial image detail outside the target zone.

 

Figure 8
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  		Figure 8. Coronal plane cone beam tomography(CBT) of a bladder, registered with the radiotherapy planning (RTP)-CT scan (inset) showing the displacement and deformation of organs in the target zone due to unexpectedly large rectal distension. The central graphic defines the clinical target volume (CTV) and the outer graphic the planning target volume (PTV).

 

Figure 9
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  		Figure 9. Matched radiotherapy planning(RTP)-CT and cone beam tomography (CBT) image volumes on the Pinnacle treatment planning system. (a) RTP-CT axial and coronal, 5 mm sections with inner clinical target volume (CTV) and planning target volume (PTV). (b) CBT axial and coronal, 1 mm sections with registered CTV and PTV. (c) CBT axial and coronal, 5 mm equivalent sections for comparison.

 

Figure 10
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  		Figure 10. Comparison of breast simulator-CT and cone beam tomography (CBT) in the treatment room. (a) Transverse sim-CT section with breast and lung contours. (b) Treatment room CBT axial (1 mm equivalent slice thickness) overlaid with simulation contours. (c) CBT coronal section (1 mm equivalence slice thickness).

 

Figure 11
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  		Figure 11. (a) Cone beam tomography (CBT) coronal image generated from profiles gathered between treatment beam deliveries. (b) CBT coronal image for the same patient generated from image profiles gathered in a single continuous post-treatment scan.

 




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