Daily electronic portal imaging of implanted gold seed fiducials in patients undergoing radiotherapy after radical prostatectomy.
OBJECTIVE
The aim of this study was to measure interfraction prostate bed motion, setup error, and total positioning error in 10 consecutive patients undergoing postprostatectomy radiotherapy.


METHODS
Daily image-guided target localization and alignment using electronic portal imaging of gold seed fiducials implanted into the prostate bed under transrectal ultrasound guidance was used in 10 patients undergoing adjuvant or salvage radiotherapy after prostatectomy. Prostate bed motion, setup error, and total positioning error were measured by analysis of gold seed fiducial location on the daily electronic portal images compared with the digitally reconstructed radiographs from the treatment-planning CT.


RESULTS
Mean (+/- standard deviation) prostate bed motion was 0.3 +/- 0.9 mm, 0.4 +/- 2.4 mm, and -1.1 +/- 2.1 mm in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP) axes, respectively. Mean set-up error was 0.1 +/- 4.5 mm, 1.1 +/- 3.9 mm, and -0.2 +/- 5.1 mm in the LR, SI, and AP axes, respectively. Mean total positioning error was 0.2 +/- 4.5 mm, 1.2 +/- 5.1 mm, and -0.3 +/- 4.5 mm in the LR, SI, and AP axes, respectively. Total positioning errors >5 mm occurred in 14.1%, 38.7%, and 28.2% of all fractions in the LR, SI, and AP axes, respectively. There was no significant migration of the gold marker seeds.


CONCLUSIONS
This study validates the use of daily image-guided target localization and alignment using electronic portal imaging of implanted gold seed fiducials as a valuable method to correct for interfraction target motion and to improve precision in the delivery of postprostatectomy radiotherapy.
Schiffner
Daniel C
DC
Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA 94143-1708, USA.
Gottschalk
Alexander R
AR
Lometti
Michael
M
Aubin
Michele
M
Pouliot
Jean
J
Speight
Joycelyn
J
Hsu
I-Chow
IC
Shinohara
Katsuto
K
Roach
Mack
M
D002138:Calibration; D006046:Gold; D006801:Humans; D008297:Male; D009068:Movement; D011467:Prostate / Q000000981:diagnostic imaging* / Q000601:surgery; D011468:Prostatectomy; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy / Q000601:surgery; D019736:Prostheses and Implants; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D018714:Radiotherapy, Adjuvant; D016879:Salvage Therapy
D006046:Gold