Abstract
BackgroundEvaluation 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.MethodsSetup 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.ResultsA 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.ConclusionSetup 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.
Highlights
Evaluation of set up error detection by a transperineal ultrasound in comparison with a cone beam computed tomography (CT) (CBCT) based system in external beam radiation therapy (EBRT) of prostate cancer
Setup error distribution of transperineal ultrasound (TPUS) and cone beam CT (CBCT) imaging For CBCT imaging, setup errors ranged from −7.3 to 12.1 mm, from −12.0 to 7.7 mm and from −10.3 to
For US imaging, a larger setup error range was measured with ranges of −12.6 to 10.3 mm, −12.6 to 11.0 mm and −11.9 to 11.3 mm in lateral, vertical and longitudinal direction, respectively
Summary
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. During external beam radiation therapy (EBRT) of prostate cancer both interfractional and intrafractional movements of the prostate commonly occur. Changes in filling levels of bladder and rectum cause internal organ movements in the anterior-posterior direction [1,2,3]. The most common technique of IGRT uses cone beam computed tomography (CBCT) based systems. CBCT based systems enable a reliable detection of interfractional target organ movements, with the disadvantage of additional radiation exposure to the Richter et al Radiation Oncology (2016) 11:147 the present study is focused on the transperineal setup of the US device. There is an ongoing controversial discussion on the precision of existing US systems [4]
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