Intra-fraction motion during extreme hypofractionated radiotherapy of the prostate using pre- and post-treatment imaging.
OBJECTIVE
To determine intra-fraction displacement of the prostate during extreme hypofractionated radiotherapy using pre- and post-treatment orthogonal images with three implanted gold seed fiducial markers.


METHODS
In total, 265 image pairs were obtained from 53 patients who underwent extreme hypofractionated radiotherapy to a dose of 35 Gy in five fractions on standard linear accelerators. Position verification was obtained with orthogonal X-rays before and after treatment and were used to determine intra-fraction prostate displacement.


RESULTS
The mean intra-fraction prostate displacements were -0.03 ± 0.61 mm (one standard deviation), 0.21 ± 1.50 mm and -0.86 ± 1.73 mm in the left-right, superior-inferior and anterior-posterior directions, respectively. The mean intra-fraction displacement during the first two fractions was moderately correlated with the displacement in the remaining three fractions, with correlation coefficients of 0.63 (95% confidence interval 0.43-0.77) and 0.47 (95% confidence interval 0.22-0.65) in the superior-inferior and anterior-posterior directions, respectively. There was no significant correlation in the left-right direction with a coefficient of -0.04 (95% confidence interval -0.31-0.23).


CONCLUSIONS
The mean intra-fraction prostate displacement during a course of extreme hypofractionated radiotherapy is small. A strategy using the first two fractions to predict future displacements >5 mm warrants further validation.
Department of Radiation Oncology, University of Toronto, ON, Canada.
H
H
Quon
D A
DA
Loblaw
P C F
PC
Cheung
L
L
Holden
C
C
Tang
G
G
Pang
G
G
Morton
A
A
Mamedov
A
A
Deabreu
D057918:Fiducial Markers; D006046:Gold; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods; D014463:Ultrasonography
D006046:Gold