Webinar – Stereotactic Radiation Therapy: Evidence and Experience with SGRT – Q&A

The questions from the webinar have been sorted below into six sections:

  • Starting an SRS program
  • Center-specific information
  • Workflow
  • Time-saving
  • Open-faced masks & patient experience
  • Clinical information

Please note that each answer is preceded with the initials of the speaker who answered the questions. They refer to:

GK – Grace Kim, PhD, UC San Diego, Dept. of Radiation Medicine and Applied Sciences

JY – Josh Yamada, MD, FRCPC, Memorial Sloan Kettering Cancer Center

JL – Josh Lawson, MD, Lexington Radiation Oncology

SGRT rep – a representative from the SGRT Community

 

Starting an SRS program

What would be your top tips for a clinic considering starting a radiosurgery program using SGRT?
GK: Accurate performance check of your treatment system and associated devices.
JL: Certainly there needs to be certainty regarding the hardware involved, physics support is critical. Beyond the capabilities of the machinery, it takes some time to become accustomed to and comfortable with the large doses/fraction. A team approach works best, and start slow.
JY: A few other things to consider when starting a program would be: Still consider working together in a multidisciplinary manner with neurosurgeons, have an active program, critically review cases as a team to do QA, and improve the work flow and catch potential errors, and carefully review outcomes including toxicity as well as tumor control.

Who is responsible for insertion of the frame into the cranium?
JY: When we used the frame routinely, our neurosurgeons usually placed the frame, except when we were in a hurry and they were late, in which case I usually placed the frame.

If I don’t have a 6 Degree of Freedom couch can I still use SGRT with an open face mask for SRS treatments?
JY: SGRT is even more critical when you don’t have a 6Dof couch, because it may be the best way to evaluate rotational errors and get feedback on how well you were able to correct it, then allow real time monitoring to ensure that errors do not creep back in during treatment.

Accuracy of SGRT vs Cyberknife?
GK: In terms of accuracy of delivery, it would be comparable. maybe there is different efficiency of the treatment. -Grace

What is the face surface on QA phantom made of?
GK: That was aqua-plastic -Grace

Did you use any accuform head rests in addition to any Timo head rests? Or just the Timo head rests alone?
JL: Have used both, really whatever you like.

Did you analyze different face-less mask systems? Is one better than another?
JL: Didn’t analyze any others, just this one.
JY: When we moved away from frame based SRS, we initially adopted a hybrid bite block/head mold system but due to problems with patient motion we eventually went to an open face technology. Using SGRT to measure the amount of movement during treatment, we found that both approaches were equivalent to what we would expect with a frame based system, but the open face system was better tolerated and allowed for good surface mapping.

What is your dose grid in the treatment planning system?
GK: Calculation grid size can be down to 1 mm. I am using 1.5 mm close to 1.25 mm CT slice size.

I didn’t notice which task group provided the information for surface image guided techniques.
GK: I think it’s TG-147.

Center-specific information

How many patients have you treated at MSK with this SGRT approach?
JY: It’s likely over a thousand. As we have moved SRS into our regional networks, have made SGRT an integral part of the workflow.

What is the purpose of the BB’s on the mask?
JL: Relic really. We didn’t use them at all at UCSD but the group here felt most comfortable using them as well, though not relied upon for setup.

Workflow

What are your tolerances?
GK: General tolerance is /- 1 mm MAG, based on Winston-Lutz QA.

You monitor the surface during treatment. How often (what %) are treatments stopped and re-setup based on the surface information?
JY: In my experience, it would be less than 5% of cases requires re-positioning.
JL: Infrequently. Part of this is because treatment times are so short now, with VMAT, FFF, etc. Another contributor is patient comfort – comfortable people are less squirmy or less prone to move. i would estimate that interruptions occur <5% of the time.

Is the SGRT interfaced with the couch – can shifts be automatically sent to the couch?
SGRT rep: Yes, for some couches.

Do you use 6D couches or 4D couches with a “head adjuster”?
JL: We use 6D couch, have done 4D but not currently.
JY: Either approach can be used for treatment, SGRT is particularly useful when a 6 DoF couch is not available, and when using manual adjustments, SGRT can give instant feedback regarding positioning in rotation and translation until the positioning is perfect.

Which breath hold level do you use for the lung treatment?
JL: Varies with the patient and the lesion, as well as the size of the lesion and the margins added. We also see from the breath hold imaging how consistent a patient is with breath hold. All that said, we typically hold the beam once they exceed about 2mm. Then have them re-do breath hold and resume. Thanks, Josh

Do you find a decreased amount of CBCTs you need for SRS treatment when using SGRT?
JY: Yes, using SGRT to set the patient up during mask placement will usually save at least one CBCT that otherwise would have been used to find the baseline position… this also represents a time savings for the patient.

Do you take a new reference capture each day after your CBCT match?
GK: For the SRS case, yes. We are not necessarily want to include any deviation from yesterday reference image. -Grace
JL: Yes we do. Each day’s match is “gold standard” for that day so each day will require a new reference image.

Is there any way of determining that patient has not moved during the time of CBCT registration/shift/setting new reference? Does AlignRT track during that time?
GK: Most of the time you can monitor the surface -Grace

How do you account for breathing motion vs. patient motion for \ spine treatments?
JL: Typically there’s a pretty regular pattern of motion from respiration. So, we aren’t using SGRT for initial positioning, just monitoring during delivery. As long as the motion trace doesn’t deviate from the regular pattern seen with respiration we feel comfortable.

What thresholds do you use for motion in spine patients?
JL: All of these patients will show a periodic motion trace with regular respiration and we accept that, so however much motion is seen in this regular pattern is, I think, acceptable. Really we are using SGRT to look for a deviation in excess of this regular pattern of respiration motion. For this, the tolerance is about 2mm.

What are typical shifts you see on CBCT after initial set up with VRT (for cranial treatments)?
GK: Usually < 1 mm range if rotational displacement is correct.

Would you use 4D gating technique together with the abdominal compression?
GK: It’s possible, but it’s depends on department policy. -Grace

Why do you treat on same day as imaging instead of next day to provide adequate time for planning/QA?
JL: We don’t always, but a fair number of patients live a good distance away. Many of them prefer a longer single day vs a repeat trip. When they are same day they have MRI in the early morning and then treat end of day (sometimes lunch). Mostly this works for single lesion patients, certainly some of the folks with multiple metastases have more a more invovled/complex planning process and it wouldn’t be ideal for them.

Why do you choose the 300cGy isodose for comparison with whole brain?
JY: I wanted to demonstrate the amount of normal brain sparing that can be achieved with focal therapy for even with multiple lesions compared to a single fraction of WBRT … Clearly WBRT can’t compete with radio surgical plans.

With AlignRT when you’re out of tolerance due to patient movement and the computer senses it’s out, does the beam shut off?
GK: If your AlignRT is linked via MMI/ADI function treatment beam will be hold (same as gating) when it’s out of tolerance -Grace

How is the MRI taken on the day of treatment utilized?
For planning, done in the open mask. The patient has had diagnostic imaging done previously, but the MRI day of (or day before) is used for final registration/planning. It doesn’t have to be the day of, but a fair # of our patients live a long way from the center and will opt to have as much done on the same day as possible.

When do physics do QA for single-day treatment, and what this QA involves?
GK: IGRT Daily QA would be morning QA (as well as AlignRT Daily verification) and WL test will be additional QA before the SRS treatment. -Grace

Do the therapists find the system easy to use?
JL: Yes they do. Any change takes some accommodation but as they become increasingly familiar with the system they increasingly like it. We use the system for DIBH left breast patients as well, and the therapists feel quite comfortable using the system and that it is helping deliver treatment.

Do you do in dependent dose calc/measurement for patient QA?
GK: Patient specific QA via portal dosimetry or phantom plan with IC and EBT3. No additional secondary calculation for now -Grace

Are result discussed here specific to the AlignRT system? Have similar results been shown for sytems from other manufacturers e.g. C-Rad?
JL: These results are specific to the AlignRT system as that’s the only one we tested. I can’t say results for C-Rad because I’ve not tested it. Thanks, Josh (not Yamada)

Time-saving

Have there been time savings in treating frameless vs. frame based?
JY: The frameless approach has several workflow advantages that also translates into time savings. For example, there is no need to take down the linac for setting the room up for frame based treatment. Also multiple lesions can now be treated in almost the same time as a single lesion because it’s really the number of isocenters rather than the number of lesions that determines the time to treat. frameless patients can be worked into the regular treatment schedule very easily.

What is your average simulation to treatment time for SRS SGRT? Is this like Gamma (simulation and treatment on same day)?
JY: In our clinic, it typically takes about a week, a few days for treatment planning etc, and also logistical – scheduling the patient, this probably varies from clinic to clinic. In urgent cases, we will be able to treat within 2 days of simulation.
GK: In our department policy, it’s 5 days procedure from Sim to SRS tx. -Grace

Open-faced masks & patient experience

Do you find increased patient comfort with open faced masks?
JY: In almost all cases, patients who had frame based SRS preferred the frameless approach – even claustrophobic patients were usually fine in an open face mask.

What was patient feedback on using open mask versus the other techniques?
JY: The vast majority of patients prefer the frameless system, although some very claustrophobic patients preferred the frame.

We are concerned with loss of stability with open faced masks needed for SGRT vs full face masks., has this been an issue at all?
JY: When we moved from frame based to frameless open face mask system, we were pleasantly surprised to find that there were no differences in the ability of the patient to maintain the proper treatment over time. We measured the amount of “drift” in both a frame, and in the same patient, a frameless set up, and found that there were no appreciable differences in patient positioning comparing frames and frameless systems. It’s also very rare to stop treatment with an open mask because a patient moves off their marks. Hence we felt very comfortable with frameless treatments, and quickly recognized the advantages of image guided verification.

Is any sedation or other technique used to help the patients tolerate an open mask?
JL: Nope. People do quite well with it. I would say that less than 5% want to take diazepam or otherwise but not as a matter of routine, no. Thanks, Josh

What was the range of motion observed using the mask system?
JY: Overall, in our experience, the range of motion is within /- 1 mm, SD 0.1 mm for translational errors and rotational errors are typically within 0.2 degrees of rotation.

Dr. Yamada – what do your patients think of the open masks … and are you using SGRT in any other unique ways?
JY: We have a small series of spine SBRT patients who have been treated in lateral decubitus because of severe back pain in supine position and unable to get anesthesia for treatment. SGRT can be used to verify and monitor the patient during treatment delivery that the patient doesn’t move in lateral decubitus once the spine is aligned properly.

For cranial IGRT, what happens if the patient moves the muscles in their face (i.e. whine, smile, squint)? Would you need to re-CBCT? Can the face be used as a surrogate for the skull?
GK: Good point. it is important to educate the patient when we setup the patient. So relax and close eyes. -Grace

Clinical information

Do you find that there are better outcomes in terms of lung function, and thus quality of life with lung SBRT versus conventional surgery?
JL: I do think toxicity will favor SBRT. This is suggested by the combined data from the 2 closed trials, showing overall survival worse after surgery. These are small numbers and both trials closed early (poor accrual), but at least the suggestion is that toxicity folling lobectomy with node dissection exceeds the toxicity following SBRT. This is also suggested by the general trend of using radiation/SBRT in patients who are medically inoperable. These are people who are known not to tolerate surgery, but they do tend to tolerate SBRT reasonably well.

With the advances in technology, are you now able to treat tumors that were previously classed as inoperable?
JY: That has always been the case with radiosurgery. The marriage of imaging technology, beam-on position monitoring and conformal treatment planning and delivery has made it possible to treat in ways that were not possible or feasible with frame based systems, such as hypo-fractionation for large lesions, which likely provides better outcomes than single session SRS, the only option with a frame based system.

You mention stereotactic techniques for benign conditions – would you treat all of these in this way or are some not suitable for SGRT?
GK: If treatment regime is meant to be SRS/SRT, then surface monitoring is definitely beneficial. -Grace

Do you see these lung cancer results changing patient pathways to radiation?
JL: I think so. Patients who are medically inoperable have always gotten radiation so those aren’t “new” patients. Now they are getting SBRT instead of conventional RT though. I think the “new” patients are going to come from the population of people who are marginally operable or operable, particularly the marginally operable population. My personal belief is that SBRT is at least as good in both outcomes and toxicity as lobectomy and I think with time the trend will be towards more SBRT. Thanks, Josh

Are more clinical trials necessary to make use of SGRT routine in spine etc?
JY: Good question. For cranial, SGRT is so obviously beneficial, that a randomized trial would probably not be necessary. For the spine, I think it still needs to be clearly demonstrated that there is a strong relationship between the surface and the spinal anatomy in question. For example, imaging the anterior chest may have direct correlation to spine position, particularly in different levels of the spine, whereas direct imaging of the spine may provide more useful information during actually beam on time. SGRT could be used to make sure that there are no unexpected or gross changes in body position perhaps.
JL: I don’t think that’s likely. Specific to brain, I believe the body of available data is sufficient to say that SGRT is a reasonable approach to motion management. Regarding spine treatment, we don’t use SGRT for positioning but do use it for monitoring during treatment.