Initial results for patient setup verification using transperineal ultrasound and cone beam CT in external beam radiation therapy of prostate cancer.
BACKGROUND
Evaluation of set up error detection by a transperineal ultrasound in comparison with a cone beam CT (CBCT) based system in external beam radiation therapy (EBRT) of prostate cancer.


METHODS
Setup verification was performed with transperineal ultrasound (TPUS) and CBCT for 10 patients treated with EBRT for prostate cancer. In total, 150 ultrasound and CBCT scans were acquired in rapid succession and analyzed for setup errors. The deviation between setup errors of the two modalities was evaluated separately for each dimension.


RESULTS
A moderate correlation in lateral, vertical and longitudinal direction was observed comparing the setup errors. Mean differences between TPUS and CBCT were (-2.7 ± 2.3) mm, (3.0 ± 2.4) mm and (3.2 ± 2.7) mm in lateral, vertical and longitudinal direction, respectively. The mean Euclidean difference between TPUS and CBCT was (6.0 ± 3.1) mm. Differences up to 19.2 mm were observed between the two imaging modalities. Discrepancies between TPUS and CBCT of at least 5 mm occurred in 58 % of monitored treatment sessions.


CONCLUSIONS
Setup differences between TPUS and CBCT are 6 mm on average. Although the correlation of the setup errors determined by the two different image modalities is rather week, the combination of setup verification by CBCT and intrafraction motion monitoring by TPUS imaging can use the benefits of both imaging modalities.
Department of Radiation Oncology, University of Wuerzburg, Josef-Schneider-Str. 11, 97080, Wuerzburg, Germany. richter_a3@ukw.de.
Anne
A
Richter
Department of Radiation Oncology, University of Wuerzburg, Josef-Schneider-Str. 11, 97080, Wuerzburg, Germany.
Bülent
B
Polat
Department of Radiation Oncology, University of Wuerzburg, Josef-Schneider-Str. 11, 97080, Wuerzburg, Germany.
Ingulf
I
Lawrenz
Department of Radiation Oncology, University of Wuerzburg, Josef-Schneider-Str. 11, 97080, Wuerzburg, Germany.
Stefan
S
Weick
Department of Radiation Oncology, University of Wuerzburg, Josef-Schneider-Str. 11, 97080, Wuerzburg, Germany.
Otto
O
Sauer
Department of Radiation Oncology, University of Wuerzburg, Josef-Schneider-Str. 11, 97080, Wuerzburg, Germany.
Michael
M
Flentje
Department of Radiation Oncology, University of Wuerzburg, Josef-Schneider-Str. 11, 97080, Wuerzburg, Germany.
Frederick
F
Mantel
D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D008297:Male; D010502:Perineum; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted; D061106:Radiotherapy Setup Errors; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D014463:Ultrasonography
Cone beam CT; IGRT; Prostate cancer; Setup verification; Transperineal ultrasound