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MatriXX Resolution - Setting up the Device for Measurements

  • Updated

Alignment under a LINAC

  • Position the detector or detector-phantom assembly on the treatment couch under the LINAC head so the device electronics face away from the LINAC gun and are not within the irradiated area. For head mounting, see Section 4.6
  • If using just the detector, place the build-up plates and/or backscatter plates on the detector area.
  • Level the detector (or detector-phantom assembly) using a spirit level placed on the detector area.
    If using the miniPhantom R, please ensure the provided plastic block has been placed under the
    electronic part of the detector as a support.
  • (Optional) If using the device in wired mode, please ensure that the cables are properly connected and do not pose a tripping hazard. Plug the power supply to the power input if the external power supply is used (see Section 4.1.3).
  • Align the effective point of measurement as indicated by the markings on the sides of the device to the isocenter. Use the room-lasers, if available.
  • At the accelerator, set the field size 20 cm × 20 cm, and turn on the light field.
  • Use the adjustment functions of the patient couch (or XY-table for head mounting, see Section 4.6.2) to position the MatriXX Resolution so that the crosshair at the sensor area and the light field are superimposed so that the device in the center of the beam. Then, adjust so that the side cross markers on the miniPhantom R or on the MatriXX Resolution and the side-cross of room lasers are superimposed the device in the center of the beam.

    Left: Miss-aligned; Right: Aligned
    If the detector is slightly tilted, slightly loosen the two clamps (f3-a) that are far away from the fixture bolt (f1) (see the last photo in step 2), and give a small torque by slightly hitting one of the two legs that are far away from the fixture bolt against the tilt direction.
    IMPORTANT NOTICE: GREASE THE SCREWS OF THE FIXING CLAMPS
    If turning the fixation clamps (f3-a and f3-b) becomes difficult, you can grease the screws with PTFE spray.
    Alignment using the markers on miniPhantom R:

    1: Effective Point of Measure, 2: Room lasers, 3: Electronics, A: Inline, B: Crossline
    Alignment using the markers on MatriXX Resolution:
  • At the LINAC console, choose the first field to be irradiated.

IMPORTANT NOTICE: USE THE SIDE MARKERS FOR POSITIONING
Due to the higher uncertainty when positioning the device in the light field (diffuse penumbras and crosshair width), it is advisable to refer to the side markers that are engraved in the housing.
When using build-up plates or an energy verification plate on the device, it is convenient to use the side markers on the device or miniPhantom and room laser for the alignment.

CAUTION: ENSURE PROPER AND SAFE POSITIONING
Always ensure proper and safe positioning of the miniPhantom R on the treatment table to prevent it from falling.

 

Device Warm-up Procedure

Warm-up: For reliable results, the device should be running for at least 5 minutes prior to the first measurements.

Pre-irradiation: 26 cm × 26 cm. A small pre-irradiation dose equivalent to 1 Gy is recommended, which also allows a general check of functionality.

WARNING: ALWAYS PERFORM PRE-IRRADIATION OF THE DEVICE
To be properly operated, the device always requires the appropriate pre-irradiation.

Background Measurement: When the MatriXX Resolution device is turned on, it automatically performs
background measurements every 20 seconds.

However, unlike the manually measured background, the automatically measured background is only used for compensation; the defect pixels will not be checked, and thus they will not be removed in the analysis.

CAUTION: MEASURE THE BACKGROUND BEFORE TAKING MEASUREMENTS
At least manually measure a background once before any measurements when using matrixx resolution

Even if the background icon shows that the background has been measured (), at least manually measure the background once at the beginning of the measurement session so that the defect pixels are identified and removed in the analysis.

 

Detector Calibrations

Preconditions: The detector warm-up, pre-irradiation, and background measurment have been performed. Reference dose or dose rate has been measured.

The procedure for performing detector calibrations are detailed in Chapter 4, Section 4.3.2 RT Detector Calibrations in myQA Platform Instructions for Use.

 

Preparation of MatriXX Resolution Phantom in the TPS System

Since the measurement uses a MatriXX Resolution in a miniPhantom R, a CT scan of the device setup is required for calculating the dose TPS plan for the verification in myQA Patients. The dose plan to be verified is calculated on the CT images in the TPS.

Note that origin of the measurement system should coincide with the origin of the CT data set (this is also the DICOM origin). In the TPS, the isocenter can be positioned precisely at the DICOM origin.

 

Acquire CT Image of MatriXX Resolution

Place the MatriXX Resolution in the miniPhantom R (device-phantom assembly) and position it in the CT scanner using the alignment lasers:
If using the Virtual CT MatriXX Resolution in miniPhantom R dataset, see Section 2.5.

  • Place the MatriXX Resolution (or detector-phantom assembly) on the treatment couch and position it in the CT scanner using the alignment lasers. Align the CT origin with the isocenter markings (1).
  • Position the device phantom assembly in the CT scanner so the central point of the measurement is at the CT origin.
  • Point zero of the measurement system always coincides with point zero of the CT data set (the DICOM origin).
  • In the TPS, the isocenter can be positioned precisely at the DICOM origin.
  • Scan the entire phantom, taking care to not scan the electronics area of the MatriXX Resolution.
    A CT scan resolution of 2.5 mm or lower should be used with standard departmental scanning protocol for soft tissue (pelvis, abdomen) imaging.

 

Cross-Calibration with Calibration Chamber or Dose Readout from the TPS

  • Import the CT scan into the TPS and create an external contour of:
    • the miniPhantom R (1)
    • the MatriXX Resolution housing (2)
    • the detector (3)

Note: If required, add a support (couch) to the CT scan.

Possible mass density overrides:

    • miniPhantom R (RW3): 1.045 g/cm3
    • MatriXX Resolution detector (ABS): 1.040 g/cm3
    • Detector area (water): 1.00 g/cm3

See Section 2.1 in myQA Patients Instructions for Use for more information on densities.

  • Verify the structures against the dimensions of the phantom and MatriXX Resolution assembly (total height of the phantom and distance to isocenter).
  • On the image, set a point on the plane that corresponds to the LINAC isocenter alignment marks on phantom surface and is shown on both coronal and transverse views. Label it.
  • Find the isocenter plane and export the dose. The isocenter is set up geometrically based on the depth and central chamber position in the TPS image

For cross-calibration with a calibration chamber:

  • Align the phantom on the couch.
  • Place the chamber in the chamber insert of the miniPhantom R.
  • Attach the chamber to an electrometer, measure the background, and pre-irradiate the chamber.
  • Irradiate an open field (dimensions and MU according to open field in TPS) and write down the chamber reading.
  • Repeat the cross-calibration 3 to 4 times in order to ensure that the reading is stable.
    Note: If not done by the electrometer, apply the KTP correction and calculate the dose. Verify the                   calculated measured dose matches the dose calculated by the TPS.
    Due to artifacts on the detector layer in the coronal view, you may need to adjust the window and level of the CT to filter out the artifact.

    Alignment of MatriXX Resolution and miniPhantom R using lasers
  • Create an open 10 cm × 10 cm reference field (it is recommended to use the same algorithm as the
    patient plan) at 0° and have the system calculate the dose using a grid size of 2.5 mm or lower.
  • Find the isocenter plane and export this dose plane. It will be used for the verification in myQA Patients. The isocenter is set up geometrically based on the depth and central pixel position in the TPS image.
  • For cross checking, export the isocenter dose as the TPS reference dose. Insert a chamber into the
    phantom and measure the dose in the 10 cm × 10 cm field. Compare the TPS reference dose with the measured reference dose.
    The procedure for performing detector calibrations are detailed in Section 4.3.2 in myQA Platform
    Instructions for Use.