Intrafractional stability of the prostate using a stereotactic radiotherapy technique.
OBJECTIVE
To evaluate the stability of the prostate during stereotactic radiation therapy.


METHODS
Forty-seven patients underwent placement of three fiducial markers into the prostate as part of a pilot study of hypofractionated stereotactic radiotherapy. Portal images before and subsequent to 227 radiotherapy fractions were analyzed for prostate movement. Six patients also underwent localizing radiographs at 6-min intervals for 24 min. Relative motion of the bony landmarks and prostate markers was calculated.


RESULTS
Analysis of portal images revealed the undirected average prostate movement of 2.0 mm (superior/inferior), 1.9 mm (anterior/posterior), and 1.4 mm (right/left) with maximum standard deviation (SD) of 2.0. Analysis of radiographs at 6-min intervals showed the greatest undirected average prostate motion between 0-6 min; 1.5 mm (superior/inferior), 1.4 mm (anterior/posterior), and 0.4 mm (right/left). Beyond 6 min, movements decreased to 0.4, 0.9, and 0.8 mm, respectively. Bony landmark motion was 0.9 mm (superior/inferior), 0.9 mm (anterior/posterior), and 0.4 mm (right/left) between 0-6 min. Beyond 6 min, motion decreased to less than 0.5 mm in any direction.


CONCLUSIONS
Stereotactic prostate radiotherapy, utilizing fiducial marker localization, resulted in average intrafractional prostate movement of 2.0 mm or less. Most patient and organ movement occurs early and a settling-in period is advisable before treatment.
Madsen
Berit L
BL
Section of Radiation Oncology, Virginia Mason Medical Center, Seattle, WA, USA. ronblm@vmmc.org
Hsi
R Alex
RA
Pham
Huong T
HT
Presser
Joseph
J
Esagui
Laura
L
Corman
John
J
Myers
Lee
L
Jones
Douglas
D
D003198:Computer Simulation; D006801:Humans; D008297:Male; D009068:Movement; D010865:Pilot Projects; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted; D013238:Stereotaxic Techniques