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Share thoughts and ideas about SGRT in general and the SGRT Community.
By brownm11 United Kingdom flag

We have recently started using AlignRT and are finding that we are sometimes getting camera blockage that is causing the deltas to go out of tolerance. This is most commonly happening when treating the medial field of a breast patient.
Have others found this and what do you find is the best solution please?
Do you take a reference capture, increase the delta tolerance for that session only, change the ROI? Or anything else that may help with this?!

By marko_laaksomaa Finland flag
I think, first you need to be sure that the patient has not moved. You can test this with rotating the gantry to zero and see will the deltas return to near zero again. If deltas are still remarkably out of zero, you should perform image guidance before continuing the treatment. It is typical in FB breasts that VRT delta will drop 1-3 mm during the first minutes and even during treatment. ... 1621000622

We have used T- ROI with breast patients and “never” had issues with deltas due to camera blockages during treatment. Could you consider using ROI demonstrated in the publication? ... 0097/69366 Eventhough the primary ROI for monitoring is T- ROI, the soft tissue can be checked with postural video (setup+intrafractional), with additional ROI or with deformation workspace (setup).

Is breast- ROI more blocked than T- ROI at challenging gantry angles of 30-40° for example? Does our 10° tilt at the fixation give more visibility for the cameras than the flat breast board? Calibration things etc.?

Just to test, you can create two ROIs for the patients. If you are used to use breast-ROI and notice that its deltas are unstable due to blocking (as seems to be your issue), please pop in to second ROI whether this T-ROI for example is acting better in those cases.

If you know that it is due to blocking, I would take a reference capture for this session only in that problematic angle, check what cameras will see (black area on the reference surface is what is out of cameras visibility), continue treatment and edit ROI for the next fraction.

Regards Marko
By brownm11 United Kingdom flag
Thanks, that's very helpful. We will try the second ROI and see if we can solve it that way!
By ben_allen
Hi, we occasionally experience this and there's a few things we trouble shoot and always solve the issue.

Are the lighting levels ok?
Does the patient have a darker skin tone - adjust setting?
Is the breast itself (or any anatomy) blocking the inferior camera view of the set ROI? This can leave only 1 camera with real 'eyes on'. Increase the ROI size.
Surface capture to improve quality of the reference surface.
If this doesn't solve it, increasing the ROI generally helps. We tend to leave the tolerances where they are.

Hope this helps. Ben