# Generate digitally reconstructed radiograph from an 3DCT. How to choose different controllpoints of an arc beam?

**URL:** <https://discourse.slicer.org/t/generate-digitally-reconstructed-radiograph-from-an-3dct-how-to-choose-different-controllpoints-of-an-arc-beam/44798>\
**Category:** Support\
**Tags:** slicerrt\
**Created:** [October 17, 2025, 11:59am UTC](https://discourse.slicer.org/t/generate-digitally-reconstructed-radiograph-from-an-3dct-how-to-choose-different-controllpoints-of-an-arc-beam/44798 "2025-10-17T11:59:44Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![ruju](https://avatars.discourse-cdn.com/v4/letter/r/ea666f/32.png) [@ruju](https://discourse.slicer.org/u/ruju)\
**Post date:** [October 17, 2025, 11:59am UTC](https://discourse.slicer.org/t/generate-digitally-reconstructed-radiograph-from-an-3dct-how-to-choose-different-controllpoints-of-an-arc-beam/44798/1 "2025-10-17T11:59:45Z")

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Hello,

I would like to create some DRRs from a 3DCT. I have one arc beam with some different controllpoints. If I want to generate a DRR with DDR Image Computation of this beam, it only generates a DRR for the first beam position. For me it is not possible to choose one of the other beam-controllpoints. Is there any possibility to select the other controllpoints?

Thanks for your help!

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**Author:** ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)\
**Post date:** [October 17, 2025, 6:55pm UTC](https://discourse.slicer.org/t/generate-digitally-reconstructed-radiograph-from-an-3dct-how-to-choose-different-controllpoints-of-an-arc-beam/44798/2 "2025-10-17T18:55:30Z")

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@Mik do you have any insights?

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**Author:** ![Mik](https://avatars.discourse-cdn.com/v4/letter/m/958977/32.png) [@Mik](https://discourse.slicer.org/u/Mik)\
**Post date:** [October 18, 2025, 6:53pm UTC](https://discourse.slicer.org/t/generate-digitally-reconstructed-radiograph-from-an-3dct-how-to-choose-different-controllpoints-of-an-arc-beam/44798/3 "2025-10-18T18:53:18Z")

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Arc beam sequence doesn’t have correct support, because i can’t find a test dataset to test it. If you need to calculate DRR images for a particular set of control points (beam angles, isocenter positions), its easier to execute a small script in python console.

See [Example 3 (CT Volume only, beam is set manually, isocenter is set manually)](https://github.com/SlicerRt/SlicerRT/blob/master/Docs/user_guide/modules/drr.md)

If you can share DICOM files with defined arc beam control points in RTPLAN, then support for arc beams can be done quite fast.

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**Author:** ![cpinter](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/cpinter/32/7995_2.png) [@cpinter](https://discourse.slicer.org/u/cpinter)\
**Post date:** [October 19, 2025, 7:04pm UTC](https://discourse.slicer.org/t/generate-digitally-reconstructed-radiograph-from-an-3dct-how-to-choose-different-controllpoints-of-an-arc-beam/44798/4 "2025-10-19T19:04:52Z")

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Thanks for bringing this up! @ruju a set of anonymized VMAT plan data would be a lot of help for us! @Mik I’ll ask a few new partners in case they can help us.

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**Author:** ![ruju](https://avatars.discourse-cdn.com/v4/letter/r/ea666f/32.png) [@ruju](https://discourse.slicer.org/u/ruju)\
**Post date:** [October 22, 2025, 10:00am UTC](https://discourse.slicer.org/t/generate-digitally-reconstructed-radiograph-from-an-3dct-how-to-choose-different-controllpoints-of-an-arc-beam/44798/5 "2025-10-22T10:00:34Z")

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Thank you!

Here is one data set of a phantom with CT and an arc beam in RTplan. [SwissTransfer - Send large files securely and free of charge](https://www.swisstransfer.com/d/09f869a6-6c16-4970-ab2c-bcbf3d303d40)

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**Author:** ![Mik](https://avatars.discourse-cdn.com/v4/letter/m/958977/32.png) [@Mik](https://discourse.slicer.org/u/Mik)\
**Post date:** [October 22, 2025, 11:29am UTC](https://discourse.slicer.org/t/generate-digitally-reconstructed-radiograph-from-an-3dct-how-to-choose-different-controllpoints-of-an-arc-beam/44798/6 "2025-10-22T11:29:24Z")

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For the dataset above the beam parameters are loaded as a sequence, you can choose `Sequences→Sequences`in modules menu. There you can press `Play/Pause`button, and see the behavior (movement) of the beam. Beam parameters are available for each control point via `Beams` module. DRR image will be calculated for corresponding beam orientation (control point).

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/3/3/3335dfd479fef7d13eb9e185a56d91352236c5ba.png)

Beam parameters for the last control point:

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/c/a/ca8dc5d02520b095c27b7ab661d2c1e31abf0d6c.png)

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**Author:** ![Mik](https://avatars.discourse-cdn.com/v4/letter/m/958977/32.png) [@Mik](https://discourse.slicer.org/u/Mik)\
**Post date:** [October 22, 2025, 1:07pm UTC](https://discourse.slicer.org/t/generate-digitally-reconstructed-radiograph-from-an-3dct-how-to-choose-different-controllpoints-of-an-arc-beam/44798/7 "2025-10-22T13:07:06Z")

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Minor correction, in your data SourceAxisDistance is 1000 mm, but `Beams` module says that the source distance is 2000 mm (which is wrong), you can set correct parameter in GUI interface, and get correct beam representation and DRR calculation.