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Every virtual simulation system is different. JRT offers a Centralite CT configuration that is right
for each situation. Which configuration is best for a particular application can depend on a number of
factors including whether or not the physician is available to select an isocenter at the time of the virtual
simulation, type of table motion, relative demand for virtual simulation system and treatment system,
established practices for marking and treating patients, and so on. Several key considerations include:
Using Table Motion to Shift Z
and/or Y Lines
Moving laser system cost can be reduced by minimizing the number of moving lasers in a system.
In the CML-1 system, table motion is used to shift laser lines in both the Y and Z planes. In the CML-
3 system, table motion is used to shift laser lines in the Y plane. The following are some points to
consider in deciding whether moving lasers or couch motion should be used to shift a
particular laser line.
- In systems where a couch motion is controlled by a scissor mechanism, the Z motion cannot
be adjusted without affecting the Y motion as well. Thus, in this case, adjusting Y and Z line
positions can be a two-step process.
- Couch vertical motion is limited by the position of the table relative to the opening on the CT.
Thus, moving lasers allow marks to be placed in locations that may not accessible through
couch movement.
- In a system where all three lines are controlled by moving lasers, all of the lines can be moved
with one push of the button. The time savings may be particularly important if multiple points
are to be marked.
- Vertical motion of the patient couch may not be controlled or displayed very accurately in
some systems. In these cases, moving lasers will position marks more accurately on the
patient.
- Lines positioned by moving lasers are not affected by sag, or any other non- repeatable, or nonlinear
element of couch motion.
- The sign of the moving lasers can be adjusted so that either direction is considered positive.
Table motion convention cannot be adjusted by the user, thus the therapist may be required to
change a sign of an offset before a correct table position can be calculated.
- Moving laser offsets are generally calculated from the laser zero position. In some cases, this
may require the offset be added to or subtracted from the current couch position in order to
move to the correct new position.
- If patient marking is to take place in the treatment room, then moving lasers do not provide an
advantage over fixed lasers in the virtual simulation room.
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PC Interface to Transfer Laser Positions
If the Centralite CT moving laser system controller is equipped with a PC interface, the controller
can be connected to the network to retrieve laser positions directly. The advantages of this
automated data transfer include:
- Errors due to operator entry of new laser positions are eliminated.
- Data is entered into the moving laser system almost instantaneously.
- Direction of movement (sign of offset) is automatically accounted for.
Installation Considerations
A successful moving laser system installation for CT simulation requires proper planning and room
preparation. Some of the issues that must be provided for in the room and system preparation
include:
- Appropriate mounting plates in the walls and in the ceiling for both moving laser actuators
and fixed laser modules.
- Location of the system controller.
- Switched power for the system controller and fixed laser modules.
- Conduit or other path for cable routing, and the resulting cable lengths required.
- Room layouts that may require alternate pedestal or angel bracket mounting.
- Interface to the treatment planning system, including location of the network connection, the
file format to be used, and the file transfer protocol anticipated.
In cases of new room construction, structure can be included that allows for maximum stability
of the installed lasers, and allows laser units to be recessed into the structure. Contact JRT for
complete details on installa-tion requirements and details of recommended Structures for new
construction.
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