Cyberknife Measurements with myQA SRS

The response of the myQA SRS device depends on the angle of incident radiation. In classical C-arm LINACs, the angular information is provided by the angle sensor GS+ mounted on the gantry. In this case the rotation is in a single plane and only information of two axes from the GS+ are used.

For myQA 2025-001, the firmware and calibration process of the GS+ was adapted in order to provide information for all three spatial axes^1. The procedure for updating the firmware and calibration process of the GS+ can be found in Sections 5.4. of the myQA SRS Instructions for Use.

CAUTION: POSITION THE SRS DETECTOR HORIZONTALLY
For measurements with a Cyberknife machine and an SRS Detector with a 3D GS+ angle sensor, ensure that the physical SRS Detector is positioned horizontally.
No in phantom rotation must be applied. Otherwise, the beam incident angle would be
determined incorrectly, leading to a wrong angle correction factor being applied.

CAUTION: POSITION ROBOTIC ARM TO 0° POSITION
To setup the angle sensor, the robotic arm must be positioned at vertical irradiation (0°) position.
 

Prerequisites

• The device assembly including the myQA SRS detector, fiducial plate and myQA SRS phantom is ready (see myQA SRS Instructions for Use for more information). A CT image has been taken for the assembly.

• The Cyberknife and myQA SRS device have been defined in the myQA Platform > Equipment setup workspace (see Chapter 4, myQA Platform Instructions for Use).

  

  To use the lookup table for the 6 MV FFF energy provided in the SW, define the BQI = 0.68 for the
  machine.

^1 The GS+ is based on a 3-axis accelerometer, it provides the inclination relative to the gravitational field of the earth. With this sensor it is not possible to detect the absolute orientation in space, therefore the usage of the myQA SRS device is limited to horizontal orientation, only (no in-phantom rotation).

• A patient and a project have been created for measurements in the myQA Patients > Patients/Projects
  workspace (see Section 2.3).

  

• Make sure that x-ray imaging is deactivated during beam delivery.

Procedure

• In the myQA Patients > Patients/Projects workspace, use the Open project button in the Project information section or the Home ribbon, or double-click the project in the list to open the project (see the screenshots above).

• Open the Measurement ribbon. In the Equipment group, select the myQA SRS and the machine, and then click Connect (1).

  

• Click Background to perform a background measurement (2).
• Click the Angle Sensor icon (3), and then follow instructions in Section 6.2, myQA Platform Instructions for Use, to set up the gantry angle sensor for calibration.
• Click Settings to open the Measurement Configuration dialog (4).

• In the Machine and Detector tabs, check/select/enter the parameters:
  When the GS+ is used, the In phantom rotation is deactivated (5).

  

• Click the Calibration tab. There are two Calibration options, depending if a GS+ is used.

  Note: See Section 4.3.2. in myQA Platform Instructions for Use for more information on detector calibrations.

  CAUTION: USE INFORMATIVE NAMES WITH ADDITIONAL INFORMATION
  When performing output calibrations always use informative names for the calibrations. For the myQA SRS Detector using the myQA SRS Phantom, the type of the SRS Phantom should be written in the calibration name to prevent mix-up between different types.
  Example: SRS_PhanV2_calibration_05052024
   

Calibration with GS+ mounted

• Check the Apply output calibration box (i) if desired.

  If multiple output calibrations exist, select the correct one form the dropdown list, or click the New output calibration button to create a new output calibration.

• Check the Apply gantry angle correction box (ii).

• Select the lookup table (iii) and energy / BQI (vi) for angular correction. It is recommend to use BQI = 0.68 for 6 MV (FFF).

  A LUT in the SW can be exported as a *.csv file by clicking the Export button. The LUT *.csv file can be imported into the SW by clicking the Import button.

• In the Beam detection tab, keep the default (factory setting) parameter values.

  

• Click OK. The color of the status round buttons will change accordingly.

  

Calibration without GS+ mounted

• Check the Apply output calibration box (i) if desired.

  If multiple output calibrations exist, select the correct one form the dropdown list, or click the New output calibration button to create a new output calibration.

• Check the Apply angular and source position correction box (ii).

• Select the lookup table (iii) and energy / BQI (vi) for angular correction. It is recommend to use BQI = 0.68 for 6 MV (FFF).

  A LUT in the SW can be exported as a *.csv file by clicking the Export button. The LUT *.csv file can be imported into the SW by clicking the Import button.

• Under Source position correction, click the Import button (v), then browse and select the plan path.xml file that provides the values of incident beam angles and SADs for the measurements.

  CAUTION: IMPORT CORRECTION FILE FROM CORRECT FOLDER
  Ensure you are selecting the path.xml file from the correct folder. The plan ID is visible when opening the file.

• If the SAD correction parameters should be replaced, click the Edit detector values button (vi) and then enter the new values in the corresponding boxes (vii). See Section 6.1.5, myQA Platform Instructions for Use, for the instructions on determining these parameters.

• In the Beam detection tab, keep the default (factory setting) parameter values.

  

• Click OK. The color of the status round buttons will change accordingly.

  

Continue the calibration procedure

• Select Movie mode (5), sampling time of 0.5 s, and make sure that the Frames box is not checked.

  

• Click Start (6) and then start to deliver the beams. After all beams have been delivered, press the Stop
  button, and the integral will be stored in the Measurement folder (7).

  

  A green tick (8) indicates the angular and source position corrections have been applied.

• To view the measurement settings or the incident angles, right-click the image in the list (9), then click Properties (10) in the context menu to open the Field of properties.

  

Beam Number Verification

When applying a source position correction to a measurement, the number of beams of the measurement will be compared to the number of beams in the plan path *.xml file. If there is a mismatch, no correction will be applied. An error message will appear:

The uncorrected measured integral will be provided with a red cross in the upper-left corner in the integral image.

Plan Path File Verification

It is possible that a wrong plan path xml file might be imported in Settings even if the beam number is correct. Since Cyberknife operates at a fixed dose rate, the SW calculates the Pearson Correlation Coefficient between the irradiation times of the beams and the number of MUs. If the correlation coefficient # > 0.8, the correct plan path file is used. If # < 0.8, the warning message pops up:

Automatic Post-processing

For plans with multiple targets, it may happen that some beams might not cross the sensor plane and only stray radiation can be detected. The signals of these beams are significantly smaller than others and cannot be detected with the normal process. In this case the SW automatically starts a post processing where a threshold is searched which covers all beams. During the process, a processing bar appears. Depending on the measurement time, this step can take several minutes.

After the process completed successfully, the angular and SAD corrected integral will be provided. If no adequate threshold can be found, the uncorrected integral will be stored.

Mounting Procedure

• Select a position on the gantry surface that is flat and parallel to the gantry rotation plane.

• The GS+ can be attached using the provided adhesive tapes or the dual-lock tape:

  Attaching with Adhesive Tape:

  (to permanently attach the GS+ to the selected LINAC)

  Remove the protection foil of the adhesive tapes (1) on the bottom of the unit.

  
  
  Attaching with Dual-Lock Tape:

  Remove the protection foil from one side of the dual-lock tape (2) and attach it to the base of the GS+ , then remove the protection foil from the other side of the dual lock tape.

• With the GS+ in the 0° position, place the complete unit where it will be affixed to the machine. Press firmly to secure the base on the gantry surface.
   

  

Mounting on a Cyberknife

For Cyberknife, the GS+ shall be mounted on the side wall (left or right) of the LINAC head.

When the LINAC head is oriented in vertical direction (0°) the orientation of the GS+ shall be in the 0° position (as indicated in the figure to the right).

CAUTION: ONLY MOUNT GS+ AS INDICATED 
DO NOT mount the Gantry Angle Sensor (GS+) in any other way than as specified in the instructions. A different
mounting may potentially lead to patient harm.
 

Base for Varian TrueBeam

By default, the GS+ is delivered with single-layer tape applied in four positions on the bottom of the base. Due to the curvature of the Varian TrueBeam LINAC cover panels, it is required to use an additional layer of adhesive tape in the two middle positions (3) as shown to the right. 

The user has to option to apply dual lock tape to the GS+. This allows the sensor to be easily attached and detached from multiple LINAC devices.

HALO GS+ Holder

To install the holder and GS+ in the Halcyon/Ethos LINAC:

• Drive the Linac gantry to the 0° position.
• Open the Halcyon/Ethos door and set the brakes.
• Attach the GS+ to the base via the bayonet lock to the HALO GS+ Holder. Ensure that the switches of the

• GS+ are on the bottom side.

  Note: The GS+ can be attached to the holder before or after it has been secured to the SSMM Power Box Bracket. The order of installation will be at the discretion of the user.

• Remove the fixation screws from the HALO GS+ Holder.
• Place the HALO GS+ holder on the bottom part of the SSMM Power Box Bracket, with the GS+ base plate
  extension facing down.
• Insert both fixation screws in the SSMM Power Box Bracket holes and tighten them, ensuring the holder
  is securely affixed to the machine.
• Switch on the GS+.
• Close the Halcyon/Ethos LINAC door

Note: For an installation video search for the article “How to mount the Gantry Sensor + holder for
Halcyon or Ethos machines” in our Help Center (helpcenter.iba-dosimetry.com)

CAUTION: VERIFY GANTRY ANGLE VALUES AFTER GS+ HAS FALLEN
If the GS+ has fallen, the angle values delivered to the myQA SW may be wrong. Please verify the angle values displayed in the Bluetooth Gantry Angle Sensor Selection and Setup dialog or Gantry Angle Sensor Calibration Tool dialog (Section 6.2).

Bluetooth FW Upgrade

• Download the new version of firmware file (*.ibapkg).

  IBA Dosimetry will provide the *.ibapkg file. If more information is needed, please visit the following
  website for detailed information or contact the IBA Customer Support (see contact information in
  Chapter 10).

• Switch on the myQA SRS detector.

• Right click IBADos.Core.UMS.SBRT.BluetoothFirmwareUpdate.exe > Run as administrator.

  Expected output:

  

• Double-click the GantrySensorPlusApplicationExtensionForBluetooth.exe to open the Gantry Sensor + Application Extension for Bluetooth (GS+ Application).

  Note: GS+ Application must not be opened in two PCs simultaneously during the FW update
  process.

  

• Click the Select Firmware File button, select the FW file and click Open.

• The update with begin automatically.

  Please note, if the upload does not being after 30 seconds, please exit the GS+ Application, shut down
  the myQA SRS device and restart the upgrade process.

  

• Once the update is finished, click the Finish button.

  

• Switch the myQA SRS device OFF, wait 1 minute and switch it ON again.

• In the Task Manager, check that the SRS Adapter is running.

  

• In the Logfile, the correct version can be verified. Go to Program Data > IBA Dosimetry > SBRTAdapter
  > logs to open IBADos.Core.UMS.SBRT.Server.log to check the version.

  

Firmware update procedure

CAUTION
Make sure the right device is connected prior to initiating the update process.

• Download the new version of firmware file (*.ibapkg).

  IBA Dosimetry will provide the *.ibapkg file. If more information is needed, please visit the following
  website for detailed information or contact the IBA Customer Support (see contact information in
  Chapter 10).

  CAUTION
  Please make sure to upload the right firmware version.

• Switch off any devices paired to the GS+.
• Turn on the Bluetooth in the dedicated PC. Switch on the GS+ device. Ensure the GS+ is properly initiated.

• Double-click the GantryAngleSensor.Application.exe to open the GS+ Application.

  Note: GS+ Application must not be opened in two PCs simultaneously during the FW update process.

  

• The GS+ should appear in the Detected Devices panel (1). Select the device from the list. If the device
  does not appear, see sub-section, Troubleshooting below.

  

• Go to Menu > Firmware update

  

• Click on the Restart Device for Updates button to put the GS+ in update mode.

  

• Once in update mode, click the Select Firmware File button, select the FW file and click Open.

  

• The update with begin automatically.

• Once complete, the new firmware version will be displayed in the GS+ Application dialog. Click Cancel
  to exit the device from update mode.

  

CAUTION: CHECK FIRMWARE VERSION AND CHECKSUM
Before installation of a new firmware version (update), verify the displayed checksum, to ensure the authenticity and integrity of the received firmware file.
For more information on checksum (hash) values, please contact the IBA Dosimetry Service Department (Section 10.1)
 

Calibration Tab

Some details in the Calibration tab may vary depending on the treatment machine type and the measurement device selected:

Table 6.1. Calibrations that can be initiated by users

CAUTION
Do not use a MatriXX Resolution (or a pixel detector with similar resolution) for measurements with a Cyberknife machine.

The calibrations done in myQA Platform are available to be selected. Calibration may also be created here. Selecting a calibration will turn the color of the corresponding round dot into green color in the Device Status and Calibration icon in the Measurement ribbon.

1: Factory calibration

This is a factory calibration for sensor uniformity stored inside the device. It is always applied to a
measurement.

2: Output Calibration

Calibrates the pixel reading to dose values. You can load an existing calibration or click New Output Calibration to create a new one in the Output Calibration dialog.

Since myQA SRS is dose rate dependent, it is recommended to perform the output calibration at the maximum dose rate of the dose rate calibration. For example, if 300, 600 and 1200 MU/min are used for the dose rate calibration, the output calibration should be performed at 1200 MU/Min.

For further instructions on the Output Calibration dialog, see Section 4.3.2.1.

Output calibration can be also copied from an existing one in the myQA Platform > Equipment Setup (see Section 4.3.2.4).

CAUTION: REPEAT ABSOLUTE CALIBRATION REGULARLY
Absolute drift of a device may be unnoticeable. Repeat the absolute calibration regularly. The Output Calibration should not be older than 3 months.

3: User uniformity correction

Checkmark the Apply User uniformity correction box and then select a suitable user uniformity correction file.

The user uniformity correction file can be created in the myQA Platform > Equipment setup workspace. Please refer to the description in Section 4.3.2.2.

4: Temperature / pressure calibration

The temperature and pressure are measured by the internal sensors. The Ktp factor for temperature and pressure calibrations are calculated for each measured frame using the temperature and pressure delivered by the device, respectively.

By default, the Apply Temperature Calibration and Apply Pressure Calibration boxes are selected. You can de-selected them if you don’t want to apply these calibrations.

In addition, there is an option to apply the calibration of the offset between internal and external temperature and pressure values. To do so, click the Calibrate… button and enter the values measured by the external devices.

For myQA SRS, temperature / pressure corrections are not necessarily due to the structure of the device.

5: Gantry angle correction

The gantry angle correction of a detector depends on:

• The geometry of the phantom and detector assembly
• Intrinsic angular dependence of the ionization chambers in the sensor array
• Radiation beam quality of the treatment device

To enable the gantry angle correction, the energy must be selected in the Machine tab; and beam quality index (BQI) must be defined in myQA Platform - Equipment Setup - Beam Qualities.

Note: The Lookup Tables provided or created in the myQA SW are valid for all rotation angles of the treatment table.

Table 6.2. Available LUTs in the SW*

* BQI definition LUTs is performed according to IAEA TRS-398; therefore, conversion of the beam quality is needed for customers using TG-51 beam quality definition. The simple ratio of D200/D100 should not be used as beam quality specifier for the LUTs.

Apply gantry angle correction.

• Check the Apply gantry angle correction box (a).
• Select the applicable LUT (b).
• Select the corresponding Energy / BQI (c).

Import / export LUTs

A LUT in the SW can be exported as a *.csv file by clicking the Export button. The LUT *.csv file can be imported into the SW by clicking the Import button.

The factor values in a LUT should be between 0 and 2.0. When a LUT containing out-of-range factors is imported, a warning will pop up showing the number of the out-of-range factors and their locations (see an example below).

LUTs created by interpolation or extrapolation
If the user selects an energy with a BQI that does not exist in the LUT list, the software will automatically interpolate or extrapolate the values out of the two closest BQIs. For example, the LUT for an energy with BQI 0.6650 will be interpolated between the existing LUTs for 6 MV (BQI: 0.6500) and 10 MV (BQI: 0.7000). Existing LUTs are provided by default, created and/or imported by the user.

To create a user defined LUT, see Chapter 5.

Note: The LUTs provided or created in the myQA SW are valid for all rotation angles of the treatment table.

6: Dose rate calibration

When using myQA SRS with conventional LINAC, a dose rate calibration is required to be applied to the
measured data:

• Tick the Apply dose rate calibration box (d).

• Select the appropriate calibration from the existing ones (e), or click the New dose rate
  calibration button (f) to create a new one following the procedure described in Section 4.3.2.3.

  

• If the Apply dose rate calibration box is not selected, a warning tooltip appears next to the Apply dose
  rate calibration radio button in the Measurement ribbon:

  

7: Angular & source position correction

When myQA SRS is used with a Cyberknife LINAC, no dose rate calibration is required as the Cyberknife
operates at a fixed dose rate.

The Cyberknife delivers beams through a robotic arm that moves and bends around the patient to deliver radiation doses from different beam angles and at different SADs during the treatment. If the Cybeknife is used without a GS+, it is necessary to apply angular and source position correction.

• Check the Apply angular and source position correction box (g).

• Select the lookup table and energy / BQI for angular correction. For details, see sub-section, 5: Gantry angle correction, above

  

• Under Source position correction, click the Import button (h), then browse and select the plan path.xml file that provides the values of incident beam angles and SADs for the measurements.

  CAUTION : IMPORT CORRECTION FILE FROM CORRECT FOLDER
  Ensure you are selecting the path.xml file from the correct folder. The plan ID is visible when opening the file.

• For SAD Correction, the default calibration parameters, Offset and Slope of the calibration plot are preset. If the SAD correction parameters should be replaced, click the Edit detector values button (i) and then enter the new values in the corresponding boxes.

• After changing the parameter, you have the option to revert them to the default (j) or last (k) values. The procedure to determine these parameters is described below (Section 6.1.5).

  

Setting up the GS+ with Cyberknife

• After connecting the GS+, ensure that the Cyberknife is oriented to 0° (vertical orientation / perch
  position).
• Click the Angle sensor icon (3) to open the Bluetooth Angle Sensor Selection and Setup dialog opens
  (4).
• The current angle and Offsets are displayed (5) in the Selected Gantry Angle Sensor Device section.

• Click the Set to Reference button (6). The value of the indicated angle will change to 0.0°.

  

• Click the Finish button to confirm the setup.