Daily organ tracking in intensity-modulated radiotherapy of prostate cancer using an electronic portal imaging device with a dose saving acquisition mode.
OBJECTIVE
Daily use of conventional electronic portal imaging devices (EPID) for organ tracking is limited due to the relatively high dose required for high quality image acquisition. We studied the use of a novel dose saving acquisition mode (RadMode) allowing to take images with one monitor unit per image in prostate cancer patients undergoing intensity-modulated radiotherapy (IMRT) and tracking of implanted fiducial gold markers.


METHODS
Twenty five patients underwent implantation of three fiducial gold markers prior to the planning CT. Before each treatment of a course of 37 fractions, orthogonal localization images from the antero-posterior and from the lateral direction were acquired. Portal images of both the setup procedure and the five IMRT treatment beams were analyzed.


RESULTS
On average, four localization images were needed for a correct patient setup, resulting in four monitor units extra dose per fraction. The mean extra dose delivered to the patient was thereby increased by 1.2%. The procedure was precise enough to reduce the mean displacements prior to treatment to < o =0.3 mm.


CONCLUSIONS
The use of a new dose saving acquisition mode enables to perform daily EPID-based prostate tracking with a cumulative extra dose of below 1 Gy. This concept is efficiently used in IMRT-treated patients, where separation of setup beams from treatment beams is mandatory.
Vetterli
Daniel
D
Division of Medical Radiation Physics, University of Bern, Switzerland.
Thalmann
Sandrine
S
Behrensmeier
Frank
F
Kemmerling
Ludger
L
Born
Ernst J
EJ
Mini
Roberto
R
Greiner
Richard H
RH
Aebersold
Daniel M
DM
D004582:Electronics, Medical / Q000295:instrumentation*; D006046:Gold; D006801:Humans; D008297:Male; D011467:Prostate / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated; D016896:Treatment Outcome
D006046:Gold