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. ...

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

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
>
> 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

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