Deformable image registration for contour propagation from CT to cone-beam CT scans in radiotherapy of prostate cancer

Figures & data

Table I. Average DSC (range) for each contour calculated over all 36 registrations for the rigid registration and the DIR. The DSC values for the bladder with the patient exclusion (see text for details) are also shown.

Mean DSC	Prostate	Rectum	Bladder	Bladder (Patient 2–4)
Rigid	0.77 (0.65–0.86)	0.71 (0.55–0.82)	0.64 (0.33–0.87)	0.76 (0.54–0.87)
DIR	0.80 (0.65–0.87)	0.77 (0.63–0.87)	0.73 (0.34–0.91)	0.86 (0.68–0.91)

Figure 1. Patient individual DSC averaged over all scans for the prostate, rectum and bladder with corresponding range (error bars).

Figure 2. The number of scans scored according to the qualitative evaluation (good, acceptable, need of adjustment and poor) for each patient and organ, respectively.

Table II. The qualitative evaluation giving the percentage (number) of scans scored according to the classification in Table I.

Number of scans	Prostate	Rectum	Bladder
Good	6% (2)	6% (2)	0
Acceptable	39% (14)	14% (5)	33% (12)
Need of adjustment	17% (6)	3% (1)	25% (9)
Poor	39% (14)	78% (28)	42% (15)

Table III. The average DSC (over all scans and patients) for the different scores of the qualitative evaluation.

	DSC
Classification	Prostate	Rectum	Bladder
Good	0.74	0.83	N/A
Acceptable	0.81	0.83	0.88
Need of adjustment	0.80	0.85	0.67
Poor	0.80	0.76	0.64

Figure 3. The low image quality illustrated in two axial slices of two of the CBCT scans for two different patients (patient 3 - upper figure, patient 2 - lower figure) with the propagated contours from the DIR (prostate grey; rectum white and bladder black) overlaid. In addition the inabilities of the investigated DIR algorithm to handle bowel gas (upper figure) and the artefacts from the fiducial markers (lower figure) are demonstrated.