1. First results with a couch-mounted Cone Beam Computed
Tomography guidance device on a superconducting proton gantry
J.Treffert1, D. Hu1, D. Slater1, H. Zandi1, S. Pinault2, M. Mehrwald3, H. Deutschmann3, P. Steininger3, P. Jacob4
1 ProNova Solutions, Research and Development, Knoxville TN, USA
2 Leoni CIA Cable Systems SAS, Research and Development, Chartres France
3 medPhoton GmbH, Research and Development, Salzburg Austria
4 MIM Software Inc., Research and Development, Cleveland OH, USA
OBJECTIVE
Characterize the performance of the patient positioning component of the SC360 proton therapy system.
Fig 1 – Imager at coplanar
treatment position
Fig 2 – Imager at non-coplanar
treatment position
Fig 4 – Simulator, Collision Avoidance, Path
Planning Component – graphical display
Bed tracking
marker
Phantom tracking
marker
Fig 5 – Overall Positioning Accuracy
Experiment
Fig 3a – Treatment Workstation – Display 1 Fig 3b – Display 2
Fig 6 – Automated 3D/3D Rigid Registration (CBCT/Planning CT)
Assess 2D/3D Registration accuracy
Assess accuracy with low-dose
acquisition modes
RESULTS
FUTURE WORK
MATERIALS AND METHODS
The SC360 utilizes a floor-mounted six-axis robotic patient positioner (Leoni Orion)
which carries a carbon fiber patient couch with integrated x-ray imager (medPhoton
Imaging Ring). Linear translation along the couch positions the ring over the
patient’s ROI. The x-ray source and detector are independently articulated, enabling
non-isocentric imaging and the capability to capture the patient’s full axial FOV or
smaller ROIs for dose reduction. Full and short (180o+fan angle) scan volumetric
acquisition/reconstruction allow imaging at treatment position (coplanar and non-
coplanar configurations – see Fig 1-2). Planar imaging is also supported. Variable
collimation of the x-rays offers angular coverage from cone-beam to effective fan-
beam geometry to enhance image quality, particularly for adaptive PT.
Network control and safety interfaces provided by imager and positioner enable
control from a single integrated workstation (see Figure 3a-b). The location of all
moving elements reported by the devices is incorporated into an online collision
avoidance system (see Figure 4). The position of a moveable marker on the patient
couch (see Fig 5) is independently monitored via optical tracking camera (NDI
Polaris Spectra® ). The accuracy of optical tracking was verified by Radian laser
tracking to be 0.3 mm.
Image display and automated registration of treatment and planning images are
provided through integration of a component from MIM Software (Harmony®) (see
Figs 3a, 6). Manual adjustment of the registration is also provided.
The couch correction which brings tumor isocenter to beam isocenter in the proper
orientation (incorporating patient space registration transformation from MIM and
Imager, Robot and Room coordinate systems) is applied. If optical tracking reports
an error greater than 0.3 mm – up to 4 iterations of position correction are employed
to account for variation (< 3 mm) due to patient/imager loading.
Overall positioning accuracy was assessed using an anthropomorphic head
phantom (see Fig 5). An internal steel BB implanted in the phantom serves as
tumor isocenter. An NDI marker is rigidly attached to the phantom and tracked.
The phantom was imaged in a reference pose moved to target location/orientation.
Multiple acquisitions at reference pose were processed and compared to assess
variation of MIM automated registration shifts. Multiple poses (translation/rotation of
phantom) were then imaged and moved to target location/orientation and target
positions compared to the reference values.
kVp Exposure estimate Slices Voxel Size (mm)
Planning CT 120 18.7 mGy CDTI 191 1 x 1 x 2
CBCT 120 4 mGy CDBI 751 0.4 x 0.4 x 0.4
X (Patient) mm Y Z Pitch (deg) Roll Yaw
0.098(0.12 max) 0.12 (0.16) 0.23(0.29) 0.13(0.19) 0.17(0.24) 0.081(0.1)
X (IEC Room) mm Y Z
0.43 (0.58 max) 0.42 (0.62) 0.37(0.51)
Task Duration (sec)
Acquisition Full/Short 60/40
CBCT Data Available 5
Data Transfer
DICOM Conversion
<45
CBCT Data Load <5
Automated Rigid Registration <5
Achieved isocenter variation for
multiple phantom poses:
[0,10 mm] x, [0,51 mm] y
[-15o , 1.7o ] z axis rotation
Variation in automated 3D registration transformation(DICOM coordinate)