Intra- and inter-radiation therapist reproducibility of daily isocenter verification using prostatic fiducial markers.
BACKGROUND
We sought to determine the intra- and inter-radiation therapist reproducibility of a previously established matching technique for daily verification and correction of isocenter position relative to intraprostatic fiducial markers (FM).


METHODS
With the patient in the treatment position, anterior-posterior and left lateral electronic images are acquired on an amorphous silicon flat panel electronic portal imaging device. After each portal image is acquired, the therapist manually translates and aligns the fiducial markers in the image to the marker contours on the digitally reconstructed radiograph. The distances between the planned and actual isocenter location is displayed. In order to determine the reproducibility of this technique, four therapists repeated and recorded this operation two separate times on 20 previously acquired portal image datasets from two patients. The data were analyzed to obtain the mean variability in the distances measured between and within observers.


RESULTS
The mean and median intra-observer variability ranged from 0.4 to 0.7 mm and 0.3 to 0.6 mm respectively with a standard deviation of 0.4 to 1.0 mm. Inter-observer results were similar with a mean variability of 0.9 mm, a median of 0.6 mm, and a standard deviation of 0.7 mm. When using a 5 mm threshold, only 0.5% of treatments will undergo a table shift due to intra or inter-observer error, increasing to an error rate of 2.4% if this threshold were reduced to 3 mm.


CONCLUSIONS
We have found high reproducibility with a previously established method for daily verification and correction of isocenter position relative to prostatic fiducial markers using electronic portal imaging.
Ullman
Karen L
KL
Radiation Oncology Branch, Center for Cancer Research, National Cancer Institute, NIH, DHHS, Bldg 10, CRC Rm B2(SW) 3500, 9000 Rockville Pike, Bethesda, MD, 20892, USA. ullmank@mail.nih.gov
Ning
Holly
H
Susil
Robert C
RC
Ayele
Asna
A
Jocelyn
Lucresse
L
Havelos
Jan
J
Guion
Peter
P
Xie
Huchen
H
Li
Guang
G
Arora
Barbara C
BC
Cannon
Angela
A
Miller
Robert W
RW
Coleman
C Norman
CN
Camphausen
Kevin
K
Ménard
Cynthia
C
D004867:Equipment Design; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D019047:Phantoms, Imaging; D011467:Prostate / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011829:Radiation Dosage; D011859:Radiography; D011878:Radiotherapy / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results