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[SGRT Community]

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Please feel free to use this thread to ask any questions you might have for our speakers.

Questions from the event are posted below:

[adi_robinson]

How can we be confident that the patient doesn’t move whilst rotating the floor for non-coplanar treatments?

Using AlignRT, we can monitor the patient at every couch angle. At our institution we evaluated the accuracy of our AlignRT system at non-coplanar couch angles and saw submillimeter accuracy (in the order of 0.3mm). With that knowledge we are comfortable treating with non-coplanar angles and monitor the patient using SGRT.

[adi_robinson]

How can we be confident that the patient doesn’t move whilst rotating the floor for non-coplanar treatments?

Using AlignRT, we can monitor the patient at every couch angle. At our institution we evaluated the accuracy of our AlignRT system at non-coplanar couch angles and saw submillimeter accuracy (in the order of 0.3mm). With that knowledge we are comfortable treating with non-coplanar angles and monitor the patient using SGRT.

[adi_robinson]

Did you have any reflective practice in your staff training ?

When training staff on new technologies or workflows we always circle back to see if there is anything we need to improve on. After a few weeks of hands on learning we usually gather and talk about the workflow and if we feel we need more training or experience before moving to the next step or level. Only once we "mastered" a workflow we are ready to move to the next. In the context of SGRT, we started with a breast workflow, moved to DIBH, then explored other body sites until we were at every patient, every fraction.

[Rayk Nachtigall]

Do the measurements/margins calculated from SGRT necessarily correlate to PTV margins as internal organs can move independently of external anatomy?

It depends on the region and the setup (systematic) errors.

If you are treating h&n the SGRT margins can correlate to the PTV margins, but you should have a look at the general setup error and consider this, too.

In thorax treatments (breast, lung, etc.) the biggest uncertainty is the breathing motion. While techniques like DIBH may allow a correlation of the margins, free breathing (FB) is somthing different. Over a large cohort it may look narrow, but individually it can differ a few centimetres. Therefore, one should be cautios with a correlation in FB treatments.

Comming to abdomen and pelvis. A correlation between surface and internal organs (movement, and filling) would be great. Unfortunatly, it is not necessarily given. A lot comes into account, that influences the surface in these regions.
Nevertheless, this question bothers me, too, and currently I'm working on an answer with the SGRT and CBCT data.
I'll keep you updated

[adi_robinson]

What niggles did you encounter when implementing the system?

The SGRT workflow might seem complicated at first, that is the experience we had when we first implemented it, there was some pushback from several therapists that had a hard time adapting. Ignoring the BBs or markers and setting the patient up to a surface was difficult to some at first (and they felt it slows them down) however, in time they realized the benefits and advantages of SGRT vs. traditional patient setup and changed their minds.

[adi_robinson]

What is the workflow when treating? Do you recapture the surface after rotating the couch? How are we sure the patient hasn’t moved when twisting the floor?

A reference SGRT surface is captures after IGRT shifts and they reference surface is kept throughout the treatment. AlighRT will continue to monitor the patient for movement throughout the treatment. During SGRT evaluation we tested the camera performance at different non-coplanar angles and saw it has maintained its submillimeter accuracy (0.3mm). We are confident it can be used to continuously monitor the patient at any couch angle.

[adi_robinson]

Would you ever move to a setup process in breath hold only so that you could remove the need to acquire free breathing data set?

The free breathing surface helps us to do the initial patient setup. in a marker less patient setup, you cannot use the DIBH data set as your vert will be off. in addition, the free beathing can be used as backup in case the patient cannot maintain breath hold.

[aqadi]

Would you ever move to a setup process in breath hold only so that you could remove the need to acquire free breathing data set?


One of the main reasons we acquire a Free breathing scan is to obtain a baseline that allows us to ensure patient positioning and breathing is similar to what was acquired on the CT simulation day.

By utilising the free breathing dataset we can ensure that our patients are not breathing over or under their threshold limits ( baseline). Therefore, by not setting a baseline it can effect patient positioning and breathing by making it a bit difficult to achieve.

The only way we can remove the free breathing scan is if we have an alternative method of checking patients baseline. For example, saving patients refrence capture in AlignRT while they are in Free breathing in CT simulation and exporting it to treatment as a baseline, however, this method is not possible in SimRT

[kimm_fremeijer]

Would you ever move to a setup process in breath hold only so that you could remove the need to acquire free breathing data set?

Good question. In our clinic since day one we make both a breathhold as a free breathing CT scan. This was before we started setting up the patients with SGRT. This had several functions, like checking if the patient benefits from breathhold treatment, if a breathhold plan didn't work we could make a VMAT plan on the FB scan. But now we give all our left sided breast patients <70 yrs a DIBH treatment and because of Gating we can also deliver a VMAT treatment in DIBH. But in the mean time we started setting up our patients with SGRT. The benefit of setting up in FB and then checking the DIBH with the RTC, is that your breathhold is the same as on the CT scan, which results in small rotations and quick online review.

So, never say never, but at this moment, we are happy with are workflow as it is