myQA Blue Phantom2 - Setting up for Measurements

This chapter describes the setup of the water phantom system for measurements in the beam. It is assumed that the equipment has been installed and verified according to Chapter 5. Instructions for performing measurements are provided by the myQA Accept Instructions for Use.

IMPORTANT NOTICE: AWARENESS
Personnel using the water phantom system must read this chapter, as well as Chapter 11 and Chapter 5, and be fully aware of its contents.

Water Phantom Setup

The following workflow is for setting up a water phantom in a C-Arm LINAC.

Step 1:  Align the Water Phantom

• Using the lift table, position the water phantom under the treatment head. Choose the correct orientation according to the application.

  CAUTION: LOCK TABLE WHEELS
  Always lock the lift table's brakes when not moving or positioning it.

• Switch off the room light and switch on the light field of the radiation device. Open the field as much as
  possible.

• Move the lift table to align the lines on the bottom of the water phantom with the lines of the light field.

  

  Water phantom marker at bottom and light field aligned

• Lock the lift table in place using the parking brakes.
• Use the lateral adjustment knobs (1) for fine adjusting the water phantom position. Ensure that the light
  field crosshairs and the crosshairs on the bottom of the water phantom are still superimposed.
• Place the spirit level on the platform of the lift table and turn the tilt adjust hand wheels (2) to adjust the
  phantoms to a perfect horizontal position.
  

IMPORTANT NOTICE: MARKERS ON WATER PHANTOM
The alignment markers at tank bottom are intended for the initial alignment of the tank only. The references for the horizontal detector movement on the main axes are the light field crosshairs.

CAUTION: COORDINATE SYSTEM
The phantom coordinate system are indicated in one lower corner of the phantom. Choose the orientation according to the application.

CAUTION: POSITION OF THE WATER PHANTOM
Always ensure that the orientation chosen in the application software corresponds to the setup. A wrong orientation may lead to incorrect measurements.

CAUTION: INSTALL WITH CAUTION ON THE PATIENT COUCH
When installing the system on the treatment machine’s patient couch, check the maximum allowable couch load prior to filling the water phantom. Do not fill the phantom with water if this load limit may be exceeded, unless suitable couch support measures are in place.
 

Step 2: Fill the Water Phantom

• Position the water reservoir carriage close to the water phantom.

• Connect the quick coupling of the water reservoir hose (1) to the counterpart on water phantom (2), which is located at one bottom corner of the phantom; push in until it snaps on.

  

• When the desired water height is reached, press the Stop button.

CAUTION: FILL THE TANK WITH CARE
Always fill the water tank with care. Overfilling the system might cause damage or injury.
Do not remove the quick coupler from the phantom while the pump is switched on.

CAUTION: DO NOT FILL IN ADDITIONAL WATER
Do not fill the water phantom with additional water when the former proper filled water reservoirs tank is empty to avoid an overflow of the water reservoir when the phantom is drained.

IMPORTANT NOTICE: DELAY IN FILLING MODE
If the Fill button is pressed the first time after the water reservoir has been connected to the mains outlet, there is an incident waiting time of approximately 15 seconds. During this time, the electromagnetic valve is opened in order to remove the air between the pump and the electromagnetic valve.

CAUTION: POTENTIAL LEAKAGE OF THE WATER COUPLER
In case of a leaking coupler after removing the water hose, DO NOT try to fix it by using your finger or a mechanical object, e.g., screwdriver. Reconnect the water reservoir and remove the blocking particle by switching on/off the water reservoir's pump. In case the particle cannot be removed, drain the water phantom and contact IBA Service (Section 12.1).

CAUTION: REGULARLY CHECK THE WATER QUALITY
Regularly check the water quality. The water shall be clean and without any pollution by dirt / mechanical particles. Incase of water pollution by dirt / mechanical particles replace the water.

Step 3: Connect the Water Phantom to CCU-X and PC

• Place the PC in the control room, close to the accelerator control terminal.

• Place the CCU-X on a flat and stable surface in the treatment room.

  WARNING: PLACE THE CCU-X AS FAR AS POSSIBLE FROM THE BEAM
  Do not place the device closer than 2 meters to the central beam. Placing the device closer than 2 meters to the central beam might lead to damage of electronic components and/or flawed measurements.

  CAUTION: DO NOT BUILD TRAPS
  Take care about that the CCU-X and the cables are located at a safe place and persons will not come across them, especially when the room light is switched off during adjustment work at the water phantom.

• Connect the drive control cable between the CONTROL CABLE connector on the CCU-X and the
  CONTROL CABLE connector on the water phantom.

  CAUTION: UNEXPECTED MOVEMENT
  Make sure that the CCU-X is switched off before connecting the drive control cable between the CCU-X and the water phantom.

• Connect the Ethernet cable between the NETWORK connector CCU-X to the NETWORK connector on the
  PC, direct or via the local network.

  IMPORTANT NOTICE: NETWORK CONNECTION
  If the CCU-X shall be connected to the computer via the local network, ensure that the TCP/IP settings have been done before. For the first time it is recommended to use a direct Ethernet connection between CCU-X and computer to get a first fast overview of the correct communication function.
   

Warming-up the CCU-X

• Turn on the CCU-X to begin the warm-up procedure.

  The warm-up and stabilization time is 15 minutes from a cold start. Please note, if the device was sufficiently acclimatized before power-on, the warm-up time can be as short as 1 minute.

  If ionization chambers are used, the high voltage should be applied during the warm-up time. If semiconductors are used, do not apply a high voltage.

• Once the warm-up is complete the LED will turn green and the device is ready to use.

• To turn on the high voltage, click the HV Setup button in the Controller panel of myQA Accept SW:

  

  IMPORTANT NOTICE: WARM-UP TIME AND LED
  The CCU-X requires 10 minutes to warm-up. When powered on, the yellow LED will be on for the duration of the warm-up. If an error occurs with the CCU-X, the red LED will be constantly on.

  CAUTION: ALWAYS REGARD THE WARM-UP TIME OF THE CCU-X
  Always regard the warm-up time of the CCU-X. Not regarding the warm-up time of the CCU-X could lead to inaccurate measurements.

  WARNING: NO CALIBRATION PROCEDURE FOR THE TEMPERATURE AND PRESSURE
  Currently there is no calibration procedure for the temperature and pressure readings provided from the water phantom and CCU-X, therefore, automatic kTp correction must not be used for absolute measurements. Using the kTp correction for absolute measurement might lead to flawed measurements and potentially patient harm. kTp correction should only be used when performing relative measurements.

Step 5: Detector Setup

CAUTION: SET HIGH VOLTAGE TO ZERO
Always set the high voltage to zero before connecting / disconnecting detector extension cables or detectors. Of course, this is also fulfilled if the CCU-X is switched off.

CAUTION: USE SPECIFIED DETECTORS
Performance of the system cannot be assured if detectors or adapters other than those specified for the water phantom are used. Unsuitable adapters may pose a safety hazard, as high-voltage may appear on adapter or detector surfaces.

Two detectors, a field and a reference detector, are required to use the water phantom in continuous measurement mode under a LINAC. Field and reference detector should be of the same type, or if this is not possible, have at least approx. the same active volume (please note, this does not apply to the Stealth Chambers). The standard field and reference detectors for the water phantom are the CC04 ionization chambers (or diodes) and the Stealth Chamber as reference detector.

Using the continuous measurement mode of the water phantom (myQA Accept software option) has two
significant advantages compared to the systematic (integrating) measurement mode:

• It significantly reduces scanning time.
• It delivers more data points in a given time than in systematic (step-by-step) mode.

A LINAC produces pulsed radiation. If only a field detector would be connected and continuous measurement would be used, the pulsing of the beam would directly appear on the curve. The signal of a reference detector is needed in order to remove the accelerators pulsing from the curve, using real-time division of the field detector signal by the reference detector signal.

Step 5a: CC04 Setup

• Insert the detector holder’s dovetail groove into the counterpart of the scan mechanic (top side of
  slider at X-axis). Fasten the screw when the holder is in the right position, indicated by a noticeable
  “snapping”.
  
• Mount the field chamber in the detector holder and fasten it with the screw at the side.
• Insert the detector cable into the self-gluing cable clamp on the water phantom's metal frame or outer side of the tank (for pull-relief of the detector). Cable clamps are part of the tool kit, delivered with the water phantom system.

• Connect the detector cable to the chamber extension cable. Close the connector protection caps by screwing against each other.

  

• Connect the extension cable to the field sensor input of the CCU-X.

• Insert the reference chamber into the reference holder tube and fasten the chamber with the nylon
  screw at the front end. When using a Stealth Chamber attach it to the collimator of the LINAC.

  

• Mount the reference holder at a comfortable place at the water phantom mechanic frame (preferably a corner). When using a Stealth Chamber attach it to the collimator of the LINAC.
• Insert the detector cable into the clamp on the water phantom's metal frame (for pull-relief of the
  detector, see above).
• Connect the detector cable to the chamber extension cable. Close the connector protection caps by screwing against each other.
• Connect the extension cable to the reference sensor input of the CCU-X.
• Place the reference chamber with the chamber tip towards to the focus at the field’s edge (the light field
  helps to find the correct location).

IMPORTANT NOTICE: CORRECT CONNECTOR HANDLING
Connectors on detector and extension cables are susceptible to contamination and mechanical damage. Keep cables covered by the protective caps when not in use.
When connecting TNC connectors, keep the connector body steady and only rotate the swivel nut (screwing ring).

IMPORTANT NOTICE: LOCATION FOR REFERENCE CHAMBER
The reference detector should be placed well in the field as this reduces the effect of unstable field-asymmetry. On the other hand, care should be taken not to shadow the field detector with the reference detector.
The reference detector must always be within the primary radiation field to provide a stable signal. Therefore, it is recommended to review the placement of the reference detector from time to time, especially, when the field size has been changed.
When the Stealth Chamber is used in the appropriate holder it is ensured that the filed is covered and the chamber is centered. There is no need for adjustment of the detector when the filed sizes are changed.

Step 5b: Diode Setup

• Insert the detector holder’s dovetail groove into the counterpart of the scan mechanic (front side of
  slider at X-axis). Fasten the screw when the holder is in the right position, indicated by a noticeable “snapping”.

  

• Mount the field diode in the detector holder and fasten it with the screw at the side. Take care about to select the right diode with respect to the used energy (yellow = photon, blue = electron, green = stereotactic).
• Insert the detector cable into the self-gluing cable clamp on the water phantom's metal frame or outer side of the tank (for pull-relief of the detector). Cable clamps are part of the tool kit, delivered with the water phantom system.
• Connect the detector cable to the detector extension cable. Close the connector protection caps by screwing against each other.
• Connect the extension cable to the field sensor input of the e CCU-X.
• Insert the reference diode (RFD) into the reference holder tube until it appears at the other end. Put the reduction tube at the RFD stem, move both backwards into the reference holder tube and fasten them with the nylon screw at the front end. The reduction tube can be found as a part of the tool kit, delivered with the water phantom system.
  
  Reference diode including reduction tube mounted at tip of reference detector holder
• Mount the reference holder at a comfortable place at the water phantom mechanic frame (preferably a corner).
• Insert the detector cable into the clamp on the water phantom's metal frame (for pull-relief of the detector, see before).
• Connect the detector cable to the detector extension cable. Close the connector protection caps by screwing against each other.
• Connect the extension cable to the reference sensor input of the e CCU-X.

• Place the reference diode with the white dot at the chamber tip towards to the focus at the field’s edge (the light field helps to find the correct location).

  
  Reference diode positioning

IMPORTANT NOTICE: ORIENTATION OF REFERENCE DIODE
At the reference diode’s tip, there is a small white dot printed. This point indicates the best position for the beam entrance, i.e. the point should be oriented towards to the focus.

Step 6: Fine Leveling of the Water Phantom

After filling the water phantom with water, the 3-D servo frame must be leveled to the water surface. This fine leveling is done with the leveling pins mounted at the upper four corners of the phantom (Section 6.1.6.1), with the CC13 chamber (Section 6.1.6.2), or diode detectors (Section 6.1.6.3).

IMPORTANT NOTICE: INCLINE CORRECTION
The slider at the X-axis does have an option for incline corrections. The horizontal alignment of the detector can be performed with this tool easily. It is recommended to check the orthogonality of the slider (holder) every time before defining the water surface, see Section 9.1.

Step 6a: Fine Leveling with Leveling Pins

The leveling pins are used to fine-level the frame to water surface. There are two sets of pins available: the pin length = 6.2 cm (a) and 15.5 cm (b). The water should be filled to the tip of the pins.

With a lift table, both sets can be used for C-Arm LINACs at any SSDs. For special cases that the water is
filled to other levels, please use a CC chamber (Section 6.1.6.2) or diode detector (Section 6.1.6.3) for frame
leveling.

Prerequisites

• To have maximum adjustment lengths in both directions (~ 5 mm), check that the lengths of the leveling AAscrew bolt above (1) and below (2) the rail are about the same.
  
  Leveling screw
• Since the adjustment height is about +/-5 mm, please fill water to about 1 mm below the tip of the pin.

IMPORTANT NOTICE: START THE LEVELING WITH THE PIN ABOVE THE WATER SURFACE
Because the movement of the water makes the alignment difficult, it is recommended to start the leveling with the pin above the water surface.

Leveling procedure

• Look at the tip of the leveling pin from the side of the phantom. When the tip is exactly at the water surface, the tip and its mirror image form a perfect cross.
  
  Leveling pin at the water surface (seen from above the water surface line); 3: Locking screw; 4: Leveling
  screw

• If the leveling pin is not exactly at the water surface, loosen the locking screw at this corner of the servo frame. Turn the leveling screw to adjust the frame vertically so that the leveling pin and its mirror image at the water surface form a perfect cross. Then tighten the locking screw.

  IMPORTANT NOTICE: LOSS OF ORTHOGONALITY
  Do not loosen any one of the remaining three locking screws while adjusting one position; otherwise, the mechanic orthogonality might be lost.

• Repeat the above two steps for adjusting the remaining three corners of the phantom.

Exchange pin sets (optional)

• Remove the old pin by pushing the pin up from the bottom and then removing it from the top.
• Install the pins. The ring of the hold has a spring ball that locks the pin (a). Push the pin down until the pin is locked (b). The head of the pin should be flat with the holder surface (c).
  
  Inserting the pins

IMPORTANT NOTICE: FIXATION OF LEVELING PINS
Please ensure that the top of the leveling pin is aligned with the top of the Leveling Pin Holder.

CAUTION: DO NOT REMOVE LEVELING PIN HOLDER FROM FRAME
The leveling pin holders are aligned to each other. After the leveling procedure, do not remove the leveling pin holder. If removing the holders, the leveling pins must be releveled to avoid wrong alignment of the mechanical frame.

IMPORTANT NOTICE: REPEAT PHANTOM ALIGNMENT CHECK
After the phantom is filled with water, the gravity point becomes much higher; it could happen that the equipment is slightly tilted and thus the phantom alignment is no more correct against the CAX. Therefore, please perform a crosscheck light field vs. markers at phantom bottom every time you lift the phantom up and make a correction by using the Lift Table lateral alignment screws.

Step 6b: Fine Leveling with CC Chamber

This section describes the fine leveling of the water phantom's mechanical frame, using a CC chamber and the alignment cap.

IMPORTANT NOTICE: ALIGNMENT CAP DESIGN
The delivered alignment cap should be only used with the CC13 chamber. However, for the Z-direction alignment, e.g., water surface levering, it can be also used with other CC chambers.

• CC chamber is already mounted in the phantom. Have the white alignment cap ready (part of the tool kit delivered with the water phantom system).
• Unfasten the CC chamber and insert the chamber as far as possible into the alignment cap, usually until the thin black ring. The active volume (the black part) of the chamber points away from the X-axis, towards the phantom's front wall.
• Slide the chamber with the mounted alignment cap backwards until the rear edge of the alignment cap touches the field chamber holder. This should be done by pushing the alignment cap and a soft support at the chamber cable. Do not pull at the cable only; otherwise, it may happen that the chamber is no more at the right position in the alignment cap.
• Secure the chamber in the holder by closing the detector locking screw. Leave the alignment cap
  mounted.
  
  Alignment cap mounted on the CC13

• Switch on the e CCU-X control unit.

  CAUTION: UNEXPECTED MOVEMENT
  Switching on the e CCU-X may cause unexpected movements of the water phantom mechanics. Keep your hands away from the water phantom mechanics and take care that no cables or foreign parts are squeezed, which causes damages.

• With the remote control, position the chamber into one of the corners of the water phantom, approx. 5 cm away from each wall and at the water surface.

• To check whether the chamber is really at the water surface, turn the alignment cap so that the crossline on the front of the cap are at 45° towards the water surface. Look at the cap from below the water surface. The exact water surface position (1) is reached if the lines form a precise cross (see the figure below).
  
  CC04 exactly at water surface (seen from below the water surface line); Blue line represent water line

  IMPORTANT NOTICE: START OF LEVELING
  Always begin the leveling adjustment from below the water surface.

• Ensure that at the starting corner the chamber is exactly at the water surface. Do not use the leveling mechanism here, only position the chamber with the remote control.
• Store the current chamber position as position A on the remote control.
  

• With the remote controls joystick, move the chamber horizontally to the next corner of the water phantom.

  IMPORTANT NOTICE: NO MOVEMENT OF SERVO DURING LEVELING
  Do not move the servo vertically during the leveling procedure.

• Store this position as position B on the remote control.
• Look at the alignment cap. If the chamber is not exactly at the water surface, loosen the locking screw at this corner of the servo frame. Turn the leveling screw to adjust the mechanical frame vertically so that the lines on the cap again form a precise cross. Then tighten the locking screw.
• Repeat the aligment procedure for the remaining corners of the water phantom.

Please note, the remote control provides just three positions for storage, the water surface position can be used at the fourth corner.

IMPORTANT NOTICE: USAGE OF STORED POSITIONS
You can use the stored positions to approach easily the leveling points again.

Step 6c: Fine Leveling with Diode

• Diode and detector holder are already mounted in the phantom. 
  
  PFD diode mounted at water phantom detector support
• Switch on the e CCU-X control unit.
• To check whether the diode is really at the water surface, look at the top of the detector from below the water surface. The exact water surface position is reached if the mirror image of the detector meets the top of the detector.
  
  EFD diode exactly at water surface (from below the water surface line (1)
• Ensure that at the starting corner the diode is exactly at the water surface. Do not use the leveling mechanism here, only position the diode with the remote control.
• Store the current chamber position as position A on the remote control.
  
• With the remote controls joystick, move the detector horizontally to the next corner of the water phantom.
• Store this position as position B on the remote control.
• Look at the diode top and mirrored image. If the diode is not exactly at the water surface, loosen the locking screw at this corner of the servo frame. Turn the leveling screw to adjust the mechanical frame vertically so that the diode head and mirrored image meet at the water surface. Then tighten the locking screw.
• Repeat the aligment procedure for the remaining corners of the water phantom.

Due to that, the remote control provides just three positions for storage, the water surface position can be used at the fourth corner.

Step 7: Define Water Surface and Isocenter

• With the remote control, move the CC13 field detector to the actual water surface in the central beam (use alignment cap). If a diode is used, proceed in the same way until the mirror image of the detector meets the top of the detector.
• Check horizontal alignment – if required perform incline correction.
  
  Wheel for horizontal incline correction at X-slider
• With the remote control, define the water surface.
  
• With the remote control, move the field detector to the isocenter position in the central beam and define the isocenter position at this point.
  
• When a field detector with alignment cap is used: Turn the alignment cap at the water surface position by 45° until the line at the front of the alignment cap is equal/parallel to the water line. Now move the alignment cap to the CAX (light field cross) until the crossed lines at the alignments top are matching with the cross hair of the light field – this shall be the Isocenter position.
  
  CAX verification at field detector alignment cap
• When a diode is used: The light field’s cross hair need to be placed exactly at the center of the diodes round top surface if this area is equal with the water surface – this shall be the Isocenter position in this case.
  
  CAX verification at EFD diode

Step 8: Ready for Measurement

After the previous steps have taken place, the water phantom setup is complete and device connection should be the same as the diagram shown in Section 5.4.2.

IMPORTANT NOTICE:  CCU-X WARM-UP AND BACKGROUND SUBTRACTION 
For the  CCU-X, observe a warm-up and stabilization time of 30 minutes. If ionization chambers are used, the high voltage should be applied during the warm-up time. If semiconductors are used, do not apply a high voltage.
Background subtraction should be done initially after the warm-up time, and each time the sensitivity settings have changed. 
For absolute dose measurements, background measurements shall be done repeatedly every 30 minutes after warm-up, and each time the sensitivity settings have been changed.

From this status onwards, measurements with myQA Accept can be started. Please refer to myQA Accept
Instructions for Use for instructions.

IMPORTANT NOTICE: INFLUENCE OF WAVES
In case that there should be profile scans close to the water surface, it might be recommendable to reduce the scanning speed (see myQA Accept Instructions for Use, Measurement Queue Setup) to avoid waves, which could have negative influence to the scan quality.

CAUTION: LOCATION OF CONTROL
When the remote control is not used, do not hang it up at the phantom servo mechanic to avoid a blockage during movement.

Measurement tips

IMPORTANT NOTICE: BACKGROUND SUBTRACTION
For the  CCU-X, background subtraction should be done initially after the warm-up time, and each time the sensitivity settings have changed. For absolute dose measurements, background measurements should be done repeatedly every 30 minutes after warm-up, and each time the sensitivity settings have been changed.

IMPORTANT NOTICE: INFLUENCE OF WAVES
In case that profile scans are close to the water surface, it is recommendable to reduce the scanning speed (see myQA Accept Instructions for Use, Measurement Queue Setup) to avoid waves, which could have negative influence on the scan quality.

 CCU-X Electrometer Setup

Important for good measurement results are the right, well-adapted selection and constellation of detectors, and the associated electrometer setup in the myQA Accept software.

The  CCU-X electrometer panel provides three different, independent selectable sensitivity ranges for the Field and Reference channels:

• High
• Medium
• Low

Table 6.1. Input current ranges of sensitivities

To choose an appropriate sensitivity setting, the operator needs to estimate the measured current, in
 regards to the dose rate used.

To calculate the input current, use the following formula: I (nA) = sensitivity (nC/Gy) x dose rate (Gy/s)

With the calculated input current for the electrometer, and the known sensitivity of the selected detector, the applicable sensitivity range for the CCU-X electrometer channel can be selected.

The associated myQA Accept Instructions for Use contains additional details and instructions concerning the CCU-X control panel.

Disassembly, Transport, and Storage of Equipment

• Move the detector to the top position with the remote control.
• Connect the water hose and empty the water phantom with the water reservoir.

• When the water phantom is empty, disconnect the hose.

  Please ensure the water reservoir pump has been switched off.

• Move the lift table to its lowest position and release the down switch.
• Before disassembling cables and connectors from the CCU-X, power off the system (or at least turn off the high voltage for the electrometer channels).
• Remove the detectors and cables and close the connectors with the protection caps.
• Take a towel to clean the detector from remaining water before storage.
• Turn off the CCU-X and disconnect the controller from all cables.
• Disconnect drive control cable from the water phantom connection box.
• Store the CCU-X, detectors and cables at a safe place. Before the water phantom will be stored, remove
  remaining water from the phantom with a towel.
• Use the dust protection cover when the phantom shall be stored for a longer time.

CAUTION: TRANSPORT OF THE WATER PHANTOM
Always empty the water phantom before moving from one location to another and lower the lift table to the lowest possible position. Moving a filled water phantom could lead to injury or damage of equipment.
Always use a lift table or trolley with a minimum load capacity of at least 100 kg to transport the device. Carrying it manually may cause injury or damage.

CAUTION: DO NOT STORE WATER IN PHANTOM
Do not store the device filled with water as the Perspex walls of the phantom might distend through long-term exposure to water. Always empty the water phantom after your measurement session.

CAUTION: DO NOT LEAVE IONISATION CHAMBERS IN WATER
Never leave an ionization chamber in water longer than necessary. Increasing humidity inside the chamber can lead to faulty measurements.

CAUTION: KEEP THE CONNECTOR AWAY FROM WATER
Do not let water come into contact with the connector of the detector or cables or any air vents.

CAUTION: REMOVING THE DETECTORS AND CABLES
Do not pull on cables when removing the detector.

Packing and Shipping

To avoid damages of the equipment, use the original packing material and transport locking when shipping. The packing should be done in the reverse order as given for unpacking.

IMPORTANT NOTICE: CONTACT IBA FOR ADDITIONAL PACKING MATERIAL
When packing and shipping your water phantom first contact IBA Dosimetry (Section 12.1) to receive the proper shipping materials. For safe shipping of the water phantom the customer has the option of receiving:

• Replacement packaging materials (pallet, cardboard box, transport belt with
  clamp lock)
• A metal transport case with foam inserts