That is just not true that an iso takes 30 minutes. Nor is it common to treat more than one iso outside of brain w/sbrt on same day. And in the case of brain, I am sure Cleveland clinics is almost always using single iso for multiple lesions or gamma knife. Can’t imagine they don’t have latest varian tech. Even more absurd would be to give 40 gy in single fractions to multiple lung lesions in the same course.
I would be careful to assume everyone treats the way you do. There is tremendous variability in SBRT delivery from center to center. There are places that do abdominal compression, 4D cbct, 12 field noncoplanar static beams, non-FFF, midtreatment cbct, etc. and it is certainly true that set up, CBCT verification, and beam on time can take up 30 min per iso.
View attachment 321969Practical Considerations Arising from the Implementation of Lung Stereotactic Body Radiation Therapy (SBRT) at a Comprehensive Cancer Center
With the anticipation of improved outcomes, especially for patients with early-stage non-small cell lung cancer, stereotactic body radiation therapy (…www.sciencedirect.com
It is impossible to treat single iso multi mets on a gamma knife, the machine is only able to treat one met at a time. Literally all the beams in the machine coverge in the middle at one isocenter.
I'm just going to stop correcting all the incorrect things you are saying because we are straying from the main point of the conversation
How often do you shift?
I have convinced ours not to do this. princess Margaret data that greater than 15-18 minutes on table caused increasing intrafraction movement. We do track with vision rt.
There’s some reasoning behind a “double check“ IGRT maneuver midway through a long treatment (ie patient on table >10-15 min). A couple mm drift in all uni-D’s means patient’s 3-4mm drifted from start; I’d wanna know that and correct for it if it happened. The CBCTs can be done pretty quickly nowadays. You could try to bill for two CBCTs but I’m sure it would not work and might even cancel out both codes. Any single IGRT code edits out the others.
I do it on treatment one, and if no changes, don't do it again. Don't bill for 2 CBCTs.
The ubiquity of motion, even in anatomic areas where we traditionally don't worry 'bout motion, is a real thing. In reality it (motion effects, and random setup error) probably "evens out" over a long, fractionated course of treatment. But I'm anal, and for single fraction SRS or SBRT I always do mid-tx imaging and correct for even a mm drift in one dimension.
An after the fact cbct? I'll stick with ignorance.For one fraction SBRT spine I do CBCT every arc or every other arc and again at the end unless I'm verifying in real time with OSMS (brain cases/Hyperarc).
For multi-fraction SBRT I do CBCT at the beginning and maybe at the end depending on the case.
With FFF arcs the treatment is usually so fast that I'm not sure that most patients wiggle much at all.
You only bill for the one CBCT. But I do tend to push a lot of dose, and I am often right against OAR constraints, so I'm a little paranoid.
There have been a few publications on this for pancreas already which led to the SMART trial (NCT03621644).
I'm trying to study this prospectively for another disease site. I have retrospective data showing changes that nobody has ever described before, and I can't publish it. At first it was "that disease site doesn't change during treatment, reject" (you can't see it with CBCT so how did you ever know) and now it's "ok so you proved that it changes, what's it good for? Reject." Will keep fighting the good fight and you all can keep complaining
E pur si muove
Inside every human is a 100,000 mile long river constantly flowing and causing motion... but like @radiation said, clinically it prob doesn't make a difference for most XRT tx's (think of cardiac SBRT, the most extreme example of motion but still very good XRT outcomes knowing full well all motion wasn't compensated for). We will never control for all motion IMHO (nor should we try). One of the reasons we used to (and still do!) put pins in skulls for SRS e.g. was predicated on the fact that brain doesn't move during SRS. But it does. If you go back and look at scads of CBCTs, you'll notice things like a patient's spinal cord being in slightly different positions within the canal every day. Regarding all this: best to let go and let God!
Vision rt. For head, chest, abdomen- it should detect if pt moves on the table and it tracks respiration. What is a cone beam in the middle of lung, pancreas or cranial adding to surface monitoring?
I'm trying to study this prospectively for another disease site. I have retrospective data showing changes that nobody has ever described before, and I can't publish it. At first it was "that disease site doesn't change during treatment, reject" (you can't see it with CBCT so how did you ever know) and now it's "ok so you proved that it changes, what's it good for? Reject." Will keep fighting the good fight and you all can keep complaining
Microsoft killed the Kinect for a reason.
That’s why like to fractionate and add some margin. Errors average out, Even if there is some sort of quantum nonlocality where the tumor is simultaneously at two different locations.
In practicality, how often is this done? Respiratory cycle~3 seconds. Can the LINAC arm adjust in the sub-second domain?
I mean, when I really have to fart I'm kind of tense. Then after I fart, I can relax, and may shift my static position. At least it feels that way!
Thanks. I've always been sketched out by the Cyberknife real time imaging model. This is not helping me.
Agree with you entirely. Most of our stereotactic approaches already work quite well and penumbra helps. ITV plus margin with one CBCT reasonable to me for pretty much all body SBRT.
Internal movement. I'd imagine pancreas may be an issue.
This is the rub. If you were concerned about intrafraction motion, and you made some assumptions (dose rate same, likelihood of the catastrophic fart roughly uniform over tx time, beam time roughly 5x as long) an equivalent amount of imaging to present prostate SBRT practice would be five!!!! cbcts during that single fraction.
Here's my own in-clinic data on about ~26 CaP patients, ~96 randomly selected fractions, and this is the measured total drift after ~10 minutes on the table (do a match to fiducials, treat, and then re-image and re-match to measure intrafx motion). In any single dimension the drift is 0-1mm 90-95% of the time. But the overall total 3D drift (what you'd need to look at for PTV creation e.g.) is >2mm 20% of the time and >3mm ~5% of the time. I agree the benefit is likely small for a population (of either patients, or fractions, or both), but the NNT to catch a clinically significant drift may be "only" 50. And for that 1/50 fraction, whether it be ~2Gy or 10+Gy, a re-IGRT might lead to a meaningful correction. And heck we engage in NNT>=50 maneuvers in rad onc all the time.
How do you know that the 1 mm drift is real. When dealing with mm measurements, could this just be part of the variability in taking multiple measurements? If I measured a stable phantom to the mm fifty times wouldn’t I make some “errors”and get some “drift” in a couple cases?Here's my own in-clinic data on about ~26 CaP patients, ~96 randomly selected fractions, and this is the measured total drift after ~10 minutes on the table (do a match to fiducials, treat, and then re-image and re-match to measure intrafx motion). In any single dimension the drift is 0-1mm 90-95% of the time. But the overall total 3D drift (what you'd need to look at for PTV creation e.g.) is >2mm 20% of the time and >3mm ~5% of the time. I agree the benefit is likely small for a population (of either patients, or fractions, or both), but the NNT to catch a clinically significant drift may be "only" 50. And for that 1/50 fraction, whether it be ~2Gy or 10+Gy, a re-IGRT might lead to a meaningful correction. And heck we engage in NNT>=50 maneuvers in rad onc all the time.
(Watching election results and posting to SDN late to keep mind otherwise occupied)
