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Any favorite dose/fractionation recipes for early stage kidney SBRT? Just starting to get some cases and wondering what others are doing out there.
Stage I RCC SBRT
- Thread starter Mandelin Rain
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50/5 works for most things?
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Random musing:
Over the range of α/β = 5 to 10, 50 Gy/5 fx equals anywhere from 67.5 to 75 Gy in 15 fractions. Depending on practice setting, and technology being used for treatment, a 15 fraction regimen could well reimburse more than the SBRT regimen.
Just sayin'.
Over the range of α/β = 5 to 10, 50 Gy/5 fx equals anywhere from 67.5 to 75 Gy in 15 fractions. Depending on practice setting, and technology being used for treatment, a 15 fraction regimen could well reimburse more than the SBRT regimen.
Just sayin'.
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My experience with HCC is when the referring sends you a patient expecting SBRT, they’re confused if the plan becomes 15-20 fractions, and somewhat skeptical.
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If it's necessary, medically, because of inability to meet constraints with a 5-fx regimen (which most referrings will have zero idea as to whether that's true or not), most will likely understand as your justification.
If it's "necessary", for financial reasons, then yeah, I'd be skeptical too.
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I usually do 40-45/5. At one point CSH was doing 36/3 and said they were getting good results but I never saw them published so…
thing to know is these rarely regress that much after you treat them. SD is a win.
That's what I've seen- stability of the tumor on imaging. Fortunately haven't had any recur yet.
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Honest questions for you guys regarding SBRT for RCC. As a Urologist I'm very adept at looking at a renal mass and knowing who is a good candidate for radical, partial nephrectomy or perc ablation. Various factors affect perc ablation success, notably size of mass, proximity to the renal hilum (major blood vessels acting as a heat/cold sink preventing adequate tumor killing, proximity to renal pelvis effecting fistula risk), and abutting structures/need for a clear window to the mass.
What factors are you looking at in planning an RCC/who is not a good candidate for it? Any concerns for messing up renal vasculature for central tumors? Any effect of mass size on treatment efficacy? Concerns for stricture or fistula if near the renal pelvis? Any major constraints from surrounding structures (i.e. anterior tumors adjacent to colon, pancreas, superior adjacent to spleen, etc? I know the data is likely too limited for any real controlled analysis, but looking for the overall gestalt. What is the impact of SBRT on renal function of the surrounding tissue? I.e. if you have a centrail tumor will you also be knocking off a good amount of functional parenchyma? Also the classic teaching is RCC = radioresistant, where is the dogma from?
What factors are you looking at in planning an RCC/who is not a good candidate for it? Any concerns for messing up renal vasculature for central tumors? Any effect of mass size on treatment efficacy? Concerns for stricture or fistula if near the renal pelvis? Any major constraints from surrounding structures (i.e. anterior tumors adjacent to colon, pancreas, superior adjacent to spleen, etc? I know the data is likely too limited for any real controlled analysis, but looking for the overall gestalt. What is the impact of SBRT on renal function of the surrounding tissue? I.e. if you have a centrail tumor will you also be knocking off a good amount of functional parenchyma? Also the classic teaching is RCC = radioresistant, where is the dogma from?
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There's not a lot of data to guide us concretely on some of these questions. Ablative radiotherapy for RCC is not common, and is only becoming more common with improvements in radiotherapy precision. The 50 Gy in 5 fractions dose many of us use is extrapolated from lung cancers. RCC is radioresistant in the same way lung adenocarcinoma is. That is, a low precision palliative dose won't control it for long. An ablative dose (BED10=100Gy+) can get significantly higher control, like 90%+ 1 year for small lung cancers. What little data we have in RCC suggests that we can achieve that level of control if we can get that same dose in.
I would like the target to be a bit away from renal hilum, 1 cm or more would be best, though less may still be ok. I can always lower the dose around the hilum if necessary, but it would lower control if the tumor is in or approaching the hilum. It's also hard to know exactly what the risk of malignant hypertension is for a given dose. If we can meet TG-101 constraints I think the risk is minimal. If not, is the risk of hypertension 5%? 2%? When is it 10%+? I don't think anyone knows. I've never seen or heard of a fistula in this setting.
I do not have a hard limit on size, but if it's infiltrative through much of the kidney I will probably take out the entire function of that kidney. Conversely, if it is exophytic, there can be small bowel adjacent, attached, or that can move during the treatment course to be adjacent to the tumor. I use MRI adaptive radiotherapy to mitigate this as much as possible. That is, as small bowel moves around, I shape the dose around it. Still, if there is small bowel stuck to the tumor that's a big problem because the ablative dose needed to control the tumor will damage small bowel. You can lower the RT dose there, but your tumor control will be reduced whenever you lower dose to spare something else like bowel. I also use MR-guidance for motion management, as these are very easy to see and track during breathing during RT delivery with combination MRI-RT, raising the precision of treatment. Bowel is the main risk here, we don't worry about pancreas or spleen. Large bowel is a bit more tolerant than small bowel.
SBRT may take down the kidney function a bit but again it depends. If it's exophytic, especially sticking off the superior/inferior pole, the damage is minimal. If it's more central and endophytic, there is more function loss. We can estimate the amount of damaged kidney parenchyma depending on the exact lesion and radiation plan.
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This I can help you with. The short answer is what most people mean when they talk about how sensitive or resistant to radiation a tumor is they mean the how much (or little) radiation it takes to kill a given tumor type. Prostate is a great example. Following "standard" fraction sizes of around 2 Gy per day we deliver around 80 Gy for prostate cancer. That is a very high dose compared to things like anal SCC (50-54 Gy) or NSCLC (60 Gy) that we treat with primary radiation.
However, things get a little more complicated and again prostate is a great example. Most of our sensitivity information is based on older data using 2(ish) Gy per day which use to be the only way we could really do things without causing a lot of unwanted issues. But many tissues which are relatively resistant to small individual doses of radiation (including non-malignant tissues and tumors like prostate and RCC) are actually quite sensitive to large individual doses of radiation. This is the basis for SBRT. Recall how I said the dose of radiation needed to kill NSCLC with small fraction sizes is a good bit less than prostate (80 vs 60 Gy)? The opposite is true with SBRT. Lung SBRT doses are typically in the range of 50(ish) Gy in 4-5 fractions whereas with prostate we can get very good control with something closer to 40 Gy. Experiences with RCC are pretty similar (both to the primary tumor and metastatic deposits).
The other issue with sensitivity comes down to how you define a response. A lot of tumors (breast, most SCCs, SCLC, etc) shrink very quickly after you give them radiation. RCCs don't but stable disease is fairly common. That is another layer of complexity to the problem.
In short, how sensitive a given tumor is to radiation is fairly context dependent. What does it mean for something like RCC? Well, as long as you are not abutting bowel and there is no reason you can't give big daily fraction sizes, you can probably expect reasonable disease control with radiation. But, if the same tumor is in an anterior location and large daily fraction sizes are not an option, dropping the daily dose and upping the total prescription may not be a great option (like it would be for something like NSCLC).
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Dear DocTwoB:
Re: ramses, all of the "dose escalation is good" data in prostate cancer came from a pre-IGRT era. The prostate is known to move versus its initial position at simulation in a fashion which can make systematic (versus random, i.e. like in lung) targeting errors more likely. Systematic errors necessitate ~3 times larger "PTV fudging" versus random errors. All of the data suggesting "much higher doses of RT are needed in prostate," versus other cancers, probably reflected the fact that several of the 40-45 prostate RT fractions "air balled," whiffed, missed, etc etc, before daily online IGRT. Old timey prostate dose escalation = fraction escalation = more opportunities to hit the target.
Radioresistance is highly subjective. Much of the "dogma" on that in RCC is from an older era too. An era where very high doses couldn't be given safely because radiation wasn't as precise (IMRT is more precise/conformal than non-IMRT) or accurate (accuracy, a measure of how close something is to a target, is improved by image guidance). Before IMRT/IGRT, radiation fields had to be larger; to hit the target, they had to be larger. Radiation treatment volume is inversely proportional to the safety of the given dose. E.g., for trigeminal neuralgia, we are treating cubic-cc sized volumes safely to 85 Gy in a single fraction. If you treated the right hemi-abdomen to 10 Gy in a single fraction (a 3L volume?), you could easily kill someone quickly.
Every mammalian cell, cancer or otherwise, has a "death response" to ionizing radiation which falls on a curve which we call "linear quadratic." (It appears linear at lower doses, curvier as the dose gets higher.) Some cells' curves dip sharply at higher fraction sizes, some less sharply:
Curve B might be a renal cell carcinoma, curve A a squamous cell carcinoma (the Y-axis is logarithmic, so B is dipping down to, maybe, 0.001-0.005 there at the end of the curve and A maybe to 0.01-0.05... these are fractional ie percent survivals).
You can compare the biological effective dose (BED... an arbitrary, meaningless number by itself unless compared to another dose) by the equation:
BED = D * (1 + d/ a/b); D=total dose, a/b=alpha/beta, d=dose per fraction
50 years ago you maybe could only give 50 Gy in 25 fx to a renal tumor. Now we can give 50 Gy in 5 fx. Renal cell might have an alpha/beta of 5.
BED1 = 50 * (1+ 2/5) = 70
BED2 = 50 * (1+ 10/5) = 150
So 50/5 is 150/70ths "hotter" than 50/25, or 214% more "deadly."
Lower alpha/beta tumors are "late responding" (relatively). That is, they probably mitose at lower rates than high alpha/beta tissues. A cell will not die from RT until it attempts mitosis. Until it does, it's alive, but a "dead man walking." Hence the relative imaging stability which is seen in renal cell after SBRTing.
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Dose escalation aside, 70 Gy is still >54-60 Gy. Yes, the prostate can and does move to some extent but that accounts for a small fraction of the difference between say an anal SCC and prostate cancer. Biology plays a role here and the dose response curves you show below below are much closer to reality. Grow yourself up some PC3 cells along with a few colorectal or NSCLC lines of your choice and generate your own curves. You provided the more complex explanation of what is meant by context dependent with respect to radiosensitivity...and why it is generally outdated.
