Introducing: Our New SOMATOM go.Open Pro
We recently installed a new CT scanner as a replacement for our Aquilion/LB from 2010. Installation started on February 25, the official radiation protection survey was on March 6, 2025 (The first patient was imaged on April 8, 2025).
(On Feb. 26, the machine was still without the Direct Laser system.)
The Siemens scanner features a 85 cm wide bore (Aquilion/LB: 90 cm), a native or scan-field-of view (sFOV) of 60 cm (Aquilion/LB: 70 cm) and an extended ("HD") FOV of 85 cm. The last item is part of the RT performance Package, which also includes a 0.35 s rotation time and higher reconstruction performance. The Direct Laser system (see below) is directly attached to the Gantry cover and is used for patient marking.
At the time of writing this introduction, the scanner is still in the Physics testing phase. Features such as DirectDensity, Direct Organs, Direct i4D (using the Varian RGSC interface), TwinSpiral Dual Energy, iMAR and the Precision Matrix will hopefully unfold their power in clinical use.
Patient Table and Carbon Overlay
The maximum allowed patient weight on the Patient Table RT is 307 kg. This is well above the limit of the TrueBeam's PerfectPitch couch, which is 200 kg (if 6 DoF movements are used). A solid piece of hardware:
The flat carbon overlay is a central accessory for radiotherapy planning. However, we made the experience that it can be quite difficult to get detailed information in advance, so we would like to cover this topic in a little more detail than usual.
The Multi-Index RTP Overlay
There are a few overlay options1 for this scanner model and the 307 kg table. We ordered a Civco UCT One Piece, because we knew it from our old scanner and were quite satisfied with it. Although Siemens ordered timely, Civco was not able to deliver on time. As a bridging measure, Siemens provided their in-house Multi-Index RTP overlay. It offers indexing for both Varian and Elekta radiotherapy systems and comes with two Lok-bars.
The hollow carbon body is 240 cm long, 51.4 cm wide and 1.5 cm thick. On the backside, two solid carbon "rails" run along the full length.
Flipping the overlay shows how it is secured on the moving cradle of the patient table:
To mount it, an L-shaped latch on the Gantry side has to go into a slot in the cradle (arrow):
By pulling the overlay back, the pin on the other end snaps into the docking station. Now the couchtop is securely locked.
The big central button is used for unlocking:
Over the full length, the solid carbon rails rest on the edges of the cradle. This is why the overlay has the same load rating (307 kg) as the patient table.
So far, the Multi-Index RTP Overlay makes a good impression.
The Direct Laser System
The three lasers move in two axes. The two lasers on the sides move up and down, marking the coronal plane. The laser on top which moves laterally marks the sagittal plane. The transverse plane is fixed. The offset to the imaging plane (red CT laser) is 327.5 mm.
To check the lasers, a phantom has to be set up according to the instructions and aligned with the lasers in their zero position. Phantom scan and evaluation are fully automated. Tolerances are 1.0 mm for shifts and 0.3° for roll, pitch and yaw.
The procedure takes about 2.5 minutes.
Daily QA Procedures
This is another phantom set which is used on a daily basis. Its main component is the water phantom module:
The phantom set is inserted into a slot (arrow) on the head side of the Multi-Index RTP Overlay. We found it convenient to move the table through the Gantry and then attach the phantom set from the back side.
The fully automated "Daily QA" procedure takes about 3.5 minutes:
Two more QA procedures which are also fully automated are the Checkup, which performs more thorough self testing (8 minutes), and the Calibration, which basically performs an Air Norm calibration (4 minutes). Both procedures are without phantom.
Notes
1 The Siemens PEP Connect online training listed the following overlay options for the go.Open Pro and the 307 kg table: Qfix Quantum, Qfix kVue and Elekta iBeam evo. Our preferred option, the Civco UCT One Piece, was not mentioned in the training video. It later turned out that the two Qfix overlays are not approved for our table (Thomas Schermann, private communication), while the Civco UCT One Piece is. Load rating for the Civco is 290 kg.