Multiple Isocenters DICOMRT - DICOM

This is a discussion on Multiple Isocenters DICOMRT - DICOM ; Hi everyone, My doubt is with reference to DICOM RT. I have multiple isocenter coordinates corresponding to multiple beams. Associated with each Beam are fields Couch Angle, Collimator Angle and Gantry Angle. Each of the isocenters have different coordinate values. ...

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Thread: Multiple Isocenters DICOMRT

  1. Multiple Isocenters DICOMRT

    Hi everyone,

    My doubt is with reference to DICOM RT.

    I have multiple isocenter coordinates corresponding to multiple beams.
    Associated with each Beam are fields Couch Angle, Collimator Angle and
    Gantry Angle. Each of the isocenters have different coordinate values.
    The DICOMRT standard says that the isocenter is defined wrt the patient
    coordinate system. Assuming that the patient has moved (i assume this
    because the couch angle has a different value for the second beam),
    what coordinate frame is the second isocenter (and all subsequent
    isocenters) defined in? Please help me understand.

    many thanks,
    sb.


  2. Re: Multiple Isocenters DICOMRT

    I suggest that you repeat this question on the DICOM-RT
    mailing list at:

    http://groups.yahoo.com/group/dicomrt

    David

    chillsuraj@yahoo.co.in wrote:
    > Hi everyone,
    >
    > My doubt is with reference to DICOM RT.
    >
    > I have multiple isocenter coordinates corresponding to multiple beams.
    > Associated with each Beam are fields Couch Angle, Collimator Angle and
    > Gantry Angle. Each of the isocenters have different coordinate values.
    > The DICOMRT standard says that the isocenter is defined wrt the patient
    > coordinate system. Assuming that the patient has moved (i assume this
    > because the couch angle has a different value for the second beam),
    > what coordinate frame is the second isocenter (and all subsequent
    > isocenters) defined in? Please help me understand.
    >
    > many thanks,
    > sb.
    >


  3. Re: Multiple Isocenters DICOMRT

    chillsuraj@yahoo.co.in wrote:
    > Hi everyone,
    >
    > My doubt is with reference to DICOM RT.
    >
    > I have multiple isocenter coordinates corresponding to multiple beams.


    The isocentre is the center where all rotational axis cross and is
    theoretically a infinite point in space (because of the enormous weight
    of the machine it is more or less a small sphere like shape with a small
    diameter, preferably less than 1mm in diameter.

    (If I have some time tomorrow I will try to find a suitable image to
    illustrate my story, all literature is at my office and I am at home now)

    > Associated with each Beam are fields Couch Angle, Collimator Angle and
    > Gantry Angle. Each of the isocenters have different coordinate values.
    > The DICOMRT standard says that the isocenter is defined wrt the patient
    > coordinate system. Assuming that the patient has moved (i assume this
    > because the couch angle has a different value for the second beam),
    > what coordinate frame is the second isocenter (and all subsequent
    > isocenters) defined in? Please help me understand.


    The definition of isocentre is IMHO (I have a daily job as physicist in
    radiotherapy) not the correct term as the isocentre is a point in space
    in relevance to the treatment machine. However in daily routine we speak
    of isocentre for a treatment plan as well, altough I think this should
    really be different (maybe something for the DICOM team to discuss about):

    The isocentre as stated in the DICOM-RT definition is actually a setup
    point (most of the times it is the center of gravity of the tumor, in
    fact it is a bit more complex due to clinical considerations but that is
    not relevant here) based on the coordinates of for instance the CT made
    as a base for the treatment plan. On this isocentre many beams can be
    placed with very different setups, depending on the treatment it can be
    over ten beams, to get a full coverage of the lesion with a homogeneous
    dose. The coordinates of the isocentre are probably closely linked to
    the coordinate system that is linked to the coordinate system of the CT,
    but does not necessarily need to be the same in numerical values.

    It is possible to treat multiple lesions, where each lesion will have
    it's own setup point with one or more beams associated. Each beam will
    probably have a different set of angles for couch, gantry and collimator.

    As a patient is treated a setup point, determined in the plan, is placed
    as precise as possible in the isocentre of the machine. If this is
    achieved all parts of the machine that can rotate will rotate around the
    isocentre and hence around the setup point for the treatment plan, this
    way setup point and isocentre will not move and all beams can be
    delivered after setting up the patient once per isocentre.

    > many thanks,
    > sb.


    Hope this helps.

    Jonathan

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