The Clarity system acquires 3D-US pelvic data with a 2D abdominal US probe outfitted with positional sensors, which is swept across the patient’s region of interest. Planning target volume (PTV) was obtained by adding 10 mm margin in all directions, except toward the rectum where the margin was set to 7 mm.ĭuring the simulation session, we acquired 3-dimensional (3D) US prostate scan with the Clarity system installed in the CT-simulation room. Clinical target volume (CTV) was defined as prostate ± seminal vesicles according to clinical and imaging data. CT data were transferred to the treatment planning system (TPS) Pinnacle (Philips, Eindhoven, The Netherlands) by a local network and target volumes and organs at risk were outlined.
#Imaging daily 2 skin#
Three skin tattoos, two laterals and one anterior, were marked for position verification by alignment to a laser system.
#Imaging daily 2 full#
To optimize reproducibility, patients followed a preparation protocol with empty rectum and full bladder before CT-simulations and before each treatment session. Patients were candidates to receive curative radiotherapy to a total dose of 76–78 Gy with daily conventional fractionation of 2 Gy.Īll patients underwent simulation by helical CT-scan (Lightspeed, General Electric, Milwaukee, WI, USA) in supine position, using a leg immobilization system (Combifix-Sinmed, Civco, Kalona, IA, USA), with contiguous slices of 3 mm thickness from L4 to 2 cm below the ischeal tuberosities. The aim of the study was to verify the consistency of the positioning errors registered by the two modalities and to analyze whether the localization errors measured by AlignRT could be correlated with those measured by Clarity.įorty patients with organ confined prostate cancer, staged cT1c–cT3b N0, median iPSA 10.2 ng/ml and aged 59–81 years (mean 73 years) were enrolled in the study after adequate informed consent and following our institutional rules. In this work, we compared daily setup variations observed by two IGRT modalities relying on surface imaging by AlignRT and trans-abdominal US by Clarity (Resonant Medical, Elekta, SE) in a cohort of patients treated for prostate cancer who underwent also regular quality assurance (QA) procedure by portal imaging. Similar data were reported by an analogous study comparing AlignRT with digital portal images. We observed that measurements by this system were highly reproducible and correlated with the setup errors detected by EPID. In a previous study, we employed the surface imaging system AlignRT (VisionRT, London, UK) to analyze inter-fraction setup variations for prostate cancer.
The interest to distinguish external setup and internal target variations resides in the possibility to identify and correct each error component.Īs a matter of fact, CBCT with fiducials is considered the gold standard to detect both setup and internal organ variations but it is not usually performed daily in long course treatments because of the non-negligible dose of radiation to the patients and staff workload.Ĭompared to CBCT, surface imaging systems showed mean positioning errors in the range of 0.1 − 4.0 mm whereas 3D-US systems showed mean systematic errors in the range of 1.3–2.5 mm and random errors in the range of 2.3-2.7 mm. Some IGRT modalities detect target position accounting for the overall localization errors without distinguishing external patient setup or internal organ motion (US and electromagnetic transponders), other IGRT modalities can detect only surrogates of setup changes (surface fiducial based imaging systems, bone or other anatomical landmarks in EPID imaging) and others can capture both external setup and internal organs variations (CBCT). IGRT can be performed by imaging modalities using ionizing radiations such as cone beam computed tomography (CBCT) or electronic portal imaging device (EPID) with fiducials, or by imaging techniques not delivering ionizing radiations such as ultrasounds (US), electromagnetic transponders and surface imaging systems. To correct for daily setup errors and inter-fraction organ motion, image guided radiation therapy (IGRT) is used, allowing for decreased safety margins and reduced normal tissues irradiation. Accurate and reproducible patient setup is a prerequisite to correctly deliver fractionated radiotherapy for prostate cancer.
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