# Computing DRR to a Transformed Volume

**URL:** <https://discourse.slicer.org/t/computing-drr-to-a-transformed-volume/26142>\
**Category:** Support\
**Created:** [November 8, 2022, 2:40pm UTC](https://discourse.slicer.org/t/computing-drr-to-a-transformed-volume/26142 "2022-11-08T14:40:41Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![domP](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/domp/32/17086_2.png) [@domP](https://discourse.slicer.org/u/domP)\
**Post date:** [November 8, 2022, 2:40pm UTC](https://discourse.slicer.org/t/computing-drr-to-a-transformed-volume/26142/1 "2022-11-08T14:40:41Z")

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Hi everyone,  
is it possible to compute DRR to a transformed volume using Radiotherapy module?  
I have applied a “harden transform” (only a rotation) to a CT volume but when I compute DRR I don’t get the expected projection image.  
I have also tried to rotate the beam with the same angle using the original CT volume (not transformed) but I get a different result.

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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:** [December 1, 2022, 7:39am UTC](https://discourse.slicer.org/t/computing-drr-to-a-transformed-volume/26142/2 "2022-12-01T07:39:31Z")

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This is a known limitation. See this topic for some more details:

> [@Generate digitally reconstructed radiograph from 3DCT](https://discourse.slicer.org/t/generate-digitally-reconstructed-radiograph-from-3dct/2010/22):
>
> Which dataset: training, validation, test?