Introducing Catalyst+ HD on TrueBeam STx

Hardware Changes

Compared to the previous system, the three ceiling-mounted pods shrinked significantly in size:

(Catalyst+ in front of the Varian NDI gating camera)

Seen from above, the mounting positions on the ceiling of a standard C-arm linac look like this (click to enlarge):

(Standard C-Arm linac)

The angles C-iso-A and C-iso-B are both 116°. The positions of A and B are symmetrical with respect to the longitudinal couch axis.

However, if the cameras are mounted on a TrueBeam with cSRS license, the position of camera A is "optimized": the lateral distance of pod A increases from 1.44m to 1.49m. Longitudinally, it is shifted from 0.72m to 0.60m, and the resulting C-iso-A angle changes from 116° to 112°:

(TrueBeam with cSRS)

All this is done to avoid shadowing of the A camera by the TrueBeam's X-Ray tube housing, if the Gantry rotates during SRS treatments.

Volume Control

As an example of acceptance testing, we want to describe Volume Control. In this task, the size of the scanned volume has to be demonstrated.

An easily recognizable object is moved along the three major axes until it reaches the border of the scanned volume, which means that it is no longer visualized by the c4D software.

In the software, the scanning box is then used to measure the distance along this axis by moving each wall of the scanning volume to this point, and reading the coordinate.

In the following image, first the couch is lowered until the object disappears. The bottom of the scan volume is then moved down to "measure" Vert Min (currently: -65.0 cm), which is 65 cm below isocenter:

(Finding the size of the scanned volume.)

In Nov 2025, we upgraded our old Catalyst HD SGRT system to the latest Catalyst+ HD. Following our proven paradigm of identical treatment systems, both rooms were upgraded.

In addition to the standard installation, six Visual Coaching Light Panels (VCLPs) were installed which will be used to coach patients during gated treatments, by changing the room light color.

Certain technological advances over a period of 10 years, like higher spatial resolution, higher frame rate etc. were expected and could be confirmed¹.

Beyond that, we purchased two additional functionalities. New licenses were installed for:

• sending 6-DoF information (including Pitch/Roll/Rotation) computed by Catalyst directly to the TrueBeam and it's PerfectPitch couch ("cPerfectPitch"),
• support of frameless stereotactic workflows with even higher accuracy ("cSRS").

The basic functionalities for setting up the patient (cPosition), monitor the position intrafractionally (cMotion) and controlling the beam during gated treatments (cRespiration) were not changed².

(Photo of inroom monitor taken during acceptance.)

Acceptance

Acceptance on TrueBeam BLAU was completed on Nov 6 with the exception of items which required the presence of the Penta-Guide cubes, because they did not arrive on time³. The Penta-Guide is used to link the radiation isocenter of the TrueBeam (after CBCT procedure) with the Catalyst isocenter. Without the Penta-Guide, the (newly designed) DailyQA phantom is aligned with the room lasers which are expected to mark the radiation isocenter:

(The DailyQA phantom during acceptance.)

Historic Note

Our old Catalyst HD, installed in 2014, actually had been C-Rad's first three camera installation worldwide. Before that, Catalyst consisted of a single projector/scanner unit at 0°. With two additional side systems, Catalyst "HD" was born.

The side scanner with the serial number 0001,

was signed by our staff,

and will be exhibited⁴ in C-Rad's Museum with a commemorative plaque on it:

Notes

¹ In a typical patient positioning situation, 3D-frame rate increased from about 1 Hz to 10 Hz.
² cRespiration was already installed on the old system but never used. This is likely going to change.
³ At this point, we had a Déjà vu.
⁴ Peter Hundlinger, private communication.