Fig 1.
Definition of the proposed prostate deformation quantification metric.
The solid and dashed lines represent the prostate contours in the planning CT and CBCT scans, respectively. (a) A 2D representation of the sagittal contours of the prostate. To align the positions of the base and apex of prostate contours in the CBCT scans to those in the planning CT scan, craniocaudal views of the prostate contour in the CBCT scans were either expanded or contracted. They were returned to their original states after the alignment. (b) A 2D representation of the axial contours of a prostate. The cross mark is the CoG of the prostate in a representative slice. The arrows indicate the prostate deformation directions.
Fig 2.
Division of the prostate gland into 12 segments.
Superior-anterior (S-A), superior-posterior (S-P), superior-right (S-R), superior-left (S-L), middle-anterior (M-A), middle-posterior (M-P), middle-right (M-R), middle-left (M-L), inferior-anterior (I-A), inferior-posterior (I-P), inferior-right (I-R), and inferior-left (I-L). The prostate was divided into three approximately equal segments in the slice dimension (the first 1/3 of the prostate volume was termed the superior segment, and the last 1/3 was termed the inferior segment) and into four equal segments in each slice (anterior, posterior, right, and left segments).
Fig 3.
The relationship between radiation therapy fraction number and normalized prostate volume in 19 patients.
There was no significant time trend.
Table 1.
Values of the average prostate deformation in the manually defined segments.
Table 2.
Standard deviations of the prostate deformation in the manually defined segments.
Table 3.
Distribution of the displacement values of the prostate CoG according to magnitudes and directions.
Fig 4.
A schematic of prostate deformation obtained by aligning of the planning CT and each CBCT scan based on the center of gravity of the prostate translation.
Expansion or displacement of the rectum affects the deformation of the M-P and M-A segments of the prostate.