SBRT Bone Met Question

[fiji128]

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If there is a only a single site of osseous PSMA PET positive disease (7 years after initial definitive tx of primary) in an otherwise good performance status prostate patient, what is the largest dimension that you would consider SBRT'ing an otherwise non complicated bone met at 30 Gy in 3 fractions? Also, the patient has already been on ADT and abiraterone for about two years.

 

[HolySmokes]

I don't have a firm cutoff. If you look at the sacrum SBRT contouring guidelines, depending on the disease those volumes can easily hit up to 10-12cm. As long as you're meeting OARs and consenting for risk of fracture I think you can reasonably treat most volumes. If worried could fractionate out more and do 30-35/5.

 

[thesauce]

I don't have a firm cutoff. If you look at the sacrum SBRT contouring guidelines, depending on the disease those volumes can easily hit up to 10-12cm. As long as you're meeting OARs and consenting for risk of fracture I think you can reasonably treat most volumes. If worried could fractionate out more and do 30-35/5.

Agree completely. Size doesn’t matter 🙂

 

[Palex80]

If you have concerns about size, since you may violate constraints, go ahead and fractionate a bit more. I often do that. Just try to reach the same/equivailent BED, for instance 5 x 8 Gy.

 

[evilbooyaa]

No largest dimension for SBRT in 2022, especially for bone far away from other OARs. I do try to not put like 150% of Rx dose in a bone though... usually around 125-130%.
If in a weight bearing bone near OARs, I favor 35/5 to PTV, 40/5 to GTV or, if far from OARs, 27/3 to PTV, 30/3 to GTV. Otherwise 30/3 or 35-40/5 very reasonable

 

[sirspamalot]

Jeez, I guess 30/10 is dead? RIP patients co-pays. That paper showing preventative treatment of asymptomatic bone mets (on the other end of the size spectrum) = $BRT cash cow I guess.

 

[evilbooyaa]

For oligomet patients, yes 30/10 is dead and has good evidence for using SBRT style dosing. Thought you loved money, why you hating on a money-maker?

 

[sirspamalot]

What do you mean "I thought you loved money" - everyone loves being fairly paid by administration. I don't advocate for exploitation of patients. 30/10 is hardly dead, and in fact, VCF showed much higher rates with SBRT than EBRT. There is no doubt SBRT is reasonable for small, non spinous oligomets. it ain't reasonable for "large" destructive lesions nor is it the preferred first choice for spinal mets based on symptomatic VCF.

 

[deleted1116990]

I try to ablate small oligomets in the bone the same way I would try to in the lung or liver. I don't understand the rationale of delivering sub-ablative doses when you are not reasonably limited by surrounding tissue.

If the lesion is in the middle of the ilium or something, I will give 24 in 1 or 50 in 5.
Even in a rib, I will give 50 in 5. We give 50 in 5 to lung tumors overlapping rib all the time, and in this case you already have a pathologic fracture.

So yes, 30 in 3 no problem. But why? Get that BED up. Gross disease deserves to be killed.
If you just want to palliate then 30/10 will do just fine. So what do you want to do? Kill gross disease or palliate?

 

[sirspamalot]

Palliate for incurable life-limiting disease.

 

[evilbooyaa]

What do you mean "I thought you loved money" - everyone loves being fairly paid by administration. I don't advocate for exploitation of patients. 30/10 is hardly dead, and in fact, VCF showed much higher rates with SBRT than EBRT. There is no doubt SBRT is reasonable for small, non spinous oligomets. it ain't reasonable for "large" destructive lesions nor is it the preferred first choice for spinal mets based on symptomatic VCF.

24 in 1 and risk of VCF not the same as 35/5...

I try to ablate small oligomets in the bone the same way I would try to in the lung or liver. I don't understand the rationale of delivering sub-ablative doses when you are not reasonably limited by surrounding tissue.

If the lesion is in the middle of the ilium or something, I will give 24 in 1 or 50 in 5.
Even in a rib, I will give 50 in 5. We give 50 in 5 to lung tumors overlapping rib all the time, and in this case you already have a pathologic fracture.

So yes, 30 in 3 no problem. But why? Get that BED up. Gross disease deserves to be killed.
If you just want to palliate then 30/10 will do just fine. So what do you want to do? Kill gross disease or palliate?

Any data to justify escalating this high? Or just a gestalt that you're smarter than everyone else out there

 

[sirspamalot]

Or just a gestalt that you're smarter than everyone else out there

 

[deleted1116990]

Palliate for incurable life-limiting disease.

The academic proton center and palliative fellowship disagrees. Get out of here with your 30 in 10 MV photons, boomer. Do you still use leeches too (actually leeches might work well to heal the post-proton necrosis, hmm)

 

[Ray D. Ayshun]

35 in

. Don't make this hard.

 

[sirspamalot]

 

[deleted1116990]

24 in 1 and risk of VCF not the same as 35/5...



Any data to justify escalating this high? Or just a gestalt that you're smarter than everyone else out there

Well, who is the burden of proof on? Where did 35/5 for bone mets come from? No, I would not do 24 in 1 or 50 in 5 to an entire vertebral body or femoral head, but I said small lesion in the middle of a bone not near anything critical. The data is the same BED10 100gy data we use for other sites.

If you're not going to ablate, then why SBRT? Palliate then re-palliate if needed IMO.

Edit: this is the same reason I hate when people do 30 in 5 "sbrt" to a pelvic node or something because of nearby bowel. What are you doing? It's not symptomatic, so you are not palliating it. Fractionate it more, push the BED, and kill it if that's what you want to do.

 

[OTN]

Well, who is the burden of proof on? Where did 35/5 for bone mets come from? No, I would not do 24 in 1 or 50 in 5 to an entire vertebral body or femoral head, but I said small lesion in the middle of a bone not near anything critical. The data is the same BED10 100gy data we use for other sites.

If you're not going to ablate, then why SBRT? Palliate then re-palliate if needed IMO.

Edit: this is the same reason I hate when people do 30 in 5 "sbrt" to a pelvic node or something because of nearby bowel. What are you doing? It's not symptomatic, so you are not palliating it. Fractionate it more, push the BED, and kill it if that's what you want to do.

Data also shows that heterogeneity in SBRT dosing doesn't matter like it does in fractionated treatment. So, you can take just part of the tumor to 50 Gy and still respect bowel tolerance.

 

[RadOncDoc21]

Data also shows that heterogeneity in SBRT dosing doesn't matter like it does in fractionated treatment. So, you can take just part of the tumor to 50 Gy and still respect bowel tolerance.

Lol, rad oncs disagreeing over dose and fractionation… this is new!

 

[Ray D. Ayshun]

All dose/fractionation schemes are ablative, some are just more ablative than others.

 

[deleted1116990]

Lol, rad oncs disagreeing over dose and fractionation… this is new!

For sure it wouldn't be rad onc if we weren't lobbing personal insults at each other over bone met treatments. Reminds me of some epic chart round show downs.

I like that 1 and 5 fraction ablative range. I'm not sure about the 3 fraction option

 

[sirspamalot]

The brutal socratic method was literally the best entertainment you could buy. Unless of course, you were on the menu. Then.. not so fun. I'd say nearly bordering on sheer terror... I went to a world class malignant program that had only slightly reformed itself after multiple residents had departed.

So whatever conflict comes along since (be it a tumor board or online) it pales in comparison. Our yunglings prolly don't have such toughness built in any more.

 

[RadOncDoc21]

The brutal socratic method was literally the best entertainment you could buy. Unless of course, you were on the menu. Then.. not so fun. I'd say nearly bordering on sheer terror... I went to a world class malignant program that had only slightly reformed itself after multiple residents had departed.

So whatever conflict comes along since (be it a tumor board or online) it pales in comparison. Our yunglings prolly don't have such toughness built in any more.

Sounds like my experience. I witnessed attendings threaten to kill each other. It sucked being a resident for one and then having to either “cover” for one or try to convince the other one I had a neutral position.

 

[deleted1116990]

Sounds like my experience. I witnessed attendings threaten to kill each other. It sucked being a resident for one and then having to either “cover” for one or try to convince the other one I had a neutral position.

I witnessed the same thing. Screaming matches. Profanity. Personal insults. Then you get out of the ivory tower and realize you can't talk to people like that in the real world...

 

[Ray D. Ayshun]

I witnessed the same thing. Screaming matches. Profanity. Personal insults. Then you get out of the ivory tower and realize you can't talk to people like that in the real world...

I feel like I missed out. Just boring ass passive aggression was my experience.

 

[sirspamalot]

I heard even more insane stories from the good ol' 80's when there were no rules except survival of the fittest. By 2000, this had paid (negative) dividends and nowadays, I suspect things are pretty tame at most places. But for those that went thru the dark ages of no mercy, strike first.... never forget, never forgive.

 

[deleted1116990]

I feel like I missed out. Just boring ass passive aggression was my experience.

For sure snark and snide were the usual name of the game. But probably once a year there would be some epic fireworks that made for good stories to reminisce with former coresidents about for a life time. Sounds like there were more of those in past decades!

 

[RadOncDoc21]

Passive aggressive behavior was just part of the application process. It’s expected in our field.

 

[Ray D. Ayshun]

Passive aggressive behavior was just part of the application process. It’s expected in our field.

Sounds like 7 gy x 5 is passively aggressive. I learned well.

 

[TheWallnerus]

For sure it wouldn't be rad onc if we weren't lobbing personal insults at each other over bone met treatments. Reminds me of some epic chart round show downs.

View attachment 362980

I like that 1 and 5 fraction ablative range. I'm not sure about the 3 fraction option

I will never stop being bitter about sitting in tumor boards 10-12y ago espousing a philosophy of high dose stereotactic radiotherapy for...

bone metastases!...

and getting politely ignored or openly ridiculed.

Don't think you guys know how hard that battle was. And then one day... the battle vanished.

 

[deleted1116990]

I will never stop being bitter about sitting in tumor boards 10-12y ago espousing a philosophy of high dose stereotactic radiotherapy for...

bone metastases!...

and getting politely ignored or openly ridiculed.

Don't think you guys know how hard that battle was. And then one day... the battle vanished.

80 Gy x 1 next to brainstem? Fine!
24 Gy x 1 to iliac crest? Dear god.

 

[medgator]

I witnessed the same thing. Screaming matches. Profanity. Personal insults. Then you get out of the ivory tower and realize you can't talk to people like that in the real world...

The autists were made for staying in academia, A³ impaired and all

 

[sirspamalot]

28/2 v 24/2 (Zeng et. al this month red journal) says failure rate cut in half to 11% with no increased risk of VCF in analysis of like 600+ sites treated.

Bueller? Anyone? Bueller..

 

[sirspamalot]

Then you get out of the ivory tower and realize you can't talk to people like that in the real world...

ps. c'mon, nobody even chuckled enough for a like? This is quality humor here people.

 

[deleted1116990]

28/2 v 24/2 (Zeng et. al this month red journal) says failure rate cut in half to 11% with no increased risk of VCF in analysis of like 600+ sites treated.

Bueller? Anyone? Bueller..

Thanks. I've escalated my 3 fraction spine dose to 30 from 27 already. Will take a look at this. I've already been giving SIB to gross disease to 26 in 2 fraction and rest of VB to 24.

For spine I like the idea of lower CTV to entire VB with SIB to GTV. It's especially satisfying when it's right in the middle of the VB. Less so when bulky disease abutting cord wrapping around to the spinous process. Delivering sub-ablative dose with SBRT that will get < 100% cell kill in PTV is less than satisfying.

 

[NotMattSpraker]

Well, who is the burden of proof on? Where did 35/5 for bone mets come from? No, I would not do 24 in 1 or 50 in 5 to an entire vertebral body or femoral head, but I said small lesion in the middle of a bone not near anything critical. The data is the same BED10 100gy data we use for other sites.

If you're not going to ablate, then why SBRT? Palliate then re-palliate if needed IMO.

Edit: this is the same reason I hate when people do 30 in 5 "sbrt" to a pelvic node or something because of nearby bowel. What are you doing? It's not symptomatic, so you are not palliating it. Fractionate it more, push the BED, and kill it if that's what you want to do.

Im a little confused on this line of thinking, but am always fascinated by peoples approach and not sure there is a right or wrong answer.

I always thought the BED 100 data was about early stage NSCLC, so higher stakes on local control because it's a curative setting. When I pick a palliation strategy, its about the tumor anatomy but also the clinical setting. 8/1 is very appropriate. SBRT is also often not inappropriate. If for example you have a fit guy with painful but stable spine oligometastasis from castrate sensitive prostate cancer, you can make a data based argument that 24-28/2 or 30-35/5 is better for the patient than 20/5.

Similar goes for the flipped scenario. We know 35/5 offers good local control in the first year. If your patient has an expected OS of only about a year, what are you gaining by escalating to 50/5 other than risk to OARs? I would use 35/5 a lot in patients with metastatic sarcoma with tumors of the abdomen or of the lung in the reirradiation setting. I just didnt feel that the potential benefit of going to 50 outweighed the risks in a patient who is unlikely to live more than 1-2 years.

 

[TheWallnerus]

What does ablative mean? Seems to be a pretty squishy definition. What is the difference between a rad onc prescribing an ablative dose and Sammy Sosa walking out of the dugout and going to the plate and before the pitch saying “here’s my home run swing.” Pretty over confident, either way.

 

[CaesarRO]

I enjoyed the recent VVPN lecture by Timmerman. I think he raises some very interesting points about altering our fractionation to keep up with the new paradigms enabled by SBRT. We are still stuck in Bergongie and Tribodeau thinking.

Toxicity lessened by spacing SBRT fractions, we assume control is worse based on historical experience -- but maybe the secret for higher doses/fx is you can maintain control and lessen tox with just giving them further apart.

 

[NotMattSpraker]

I enjoyed the recent VVPN lecture by Timmerman. I think he raises some very interesting points about altering our fractionation to keep up with the new paradigms enabled by SBRT. We are still stuck in Bergongie and Tribodeau thinking.

Toxicity lessened by spacing SBRT fractions, we assume control is based on historical experience -- but maybe the secret for higher doses/fx is you can maintain control and lessen tox with just giving them further apart.

I also loved this lecture, it's great to see fresh thinking and a creative approach.

 

[OTN]

I enjoyed the recent VVPN lecture by Timmerman. I think he raises some very interesting points about altering our fractionation to keep up with the new paradigms enabled by SBRT. We are still stuck in Bergongie and Tribodeau thinking.

Toxicity lessened by spacing SBRT fractions, we assume control is based on historical experience -- but maybe the secret for higher doses/fx is you can maintain control and lessen tox with just giving them further apart.

I've changed to weekly SBRT for my prostate patients and I do believe it's made a difference in toxicity

 

[TheWallnerus]

I've changed to weekly SBRT for my prostate patients and I do believe it's made a difference in toxicity

Because it decreases the BED.

 

[OTN]

Because it decreases the BED.

True I'm sure, but as you know BED calcs for SBRT dosing levels completely fall apart.

 

[Lamount]

Spine SBRT has been around for years and has excellent LC with "subablative" fractionation, whereas in lung, we know that you probably need well higher than BID 100 Gy. Brain SRS also seems to be much more effective at lower doses. One reasonable hypothesis is that bone/brain metastases require a lower dose to control than mets in other organs -maybe it is just less hospitable in these locations for tumors to withstand treatment.

 

[Ray D. Ayshun]

My prostate bone mets scheme is 35/5 q5 years.

 

[TheWallnerus]

True I'm sure, but as you know BED calcs for SBRT dosing levels completely fall apart.

A common misconception 🙂

And anyways I'd rather prefer to believe I'm doing something scientific, predictable, and understandable... rather than doing something in which my understanding completely falls apart!

If you want to cure a tumor
Then finish radiation sooner
Give it 3 × 20 Grays [sic]
And cut the time to just 5 days.
To figure dose just use LQ
With terms that are but two.
No need to add more bits
As the patient data already fits.
So keep it simple with nothing new
Just stick with straight LQ

In Regard to Song et al.

Dose Escalation, Not “New Biology,” Can Account for the Efficacy of Stereotactic Body Radiation Therapy With Non-Small Cell Lung Cancer

 

[communitydoc13]

Because it decreases the BED.

True I'm sure, but as you know BED calcs for SBRT dosing levels completely fall apart.

To figure dose just use LQ

Per the standard LQ equation, there is no time factor. 5 fractions given over 5 weeks has the same BED as 5 fractions given over 1 week.

But, the time factor is real and is roughly accounted for in time adjusted equations.

For something like pCA, which grows slow AF unless it's not an adeno, I doubt that the "real" BED relative to tumor control changes much in going from 1 to 5 weeks. However, regarding the urethral and bladder mucosa, which has rapid cell turnover and proliferation, a week between treatments may markedly improve acute toxicity and even consequential late toxicity.

The data driving BED calcs has a lot of variance. I wouldn't put too much credence in calcs at the limits of clinical practice. (5x10 not the same as 18x3 but both work). For SIB-ing pelvic and retroperitoneal disease between 1.8 and 2.75 Gy/day, I think it's great.

 

[TheWallnerus]

Per the standard LQ equation, there is no time factor. 5 fractions given over 5 weeks has the same BED as 5 fractions given over 1 week.

But, the time factor is real and is roughly accounted for in time adjusted equations.

For something like pCA, which grows slow AF unless it's not an adeno, I doubt that the "real" BED relative to tumor control changes much in going from 1 to 5 weeks. However, regarding the urethral and bladder mucosa, which has rapid cell turnover and proliferation, a week between treatments may markedly improve acute toxicity and even consequential late toxicity.

The data driving BED calcs has a lot of variance. I wouldn't put too much credence in calcs at the limits of clinical practice. (5x10 not the same as 18x3 but both work). For SIB-ing pelvic and retroperitoneal disease between 1.8 and 2.75 Gy/day, I think it's great.

I would say time factor is a standard part of the LQ formalism, now, but as you alluded to, much less of a… factor… as the Tpot goes up.

You’re ostensibly putting credence in the calcs with eg 5x10 versus 18x3 which obviously are not the same BED but may arrive at the same local control probability estimate (ie “both work”) depending on guesstimated alpha/beta, and clonogen count.

a week between treatments may markedly improve acute toxicity and even consequential late toxicity

Again, the BED was lowered 😉

 

[evilbooyaa]

Im a little confused on this line of thinking, but am always fascinated by peoples approach and not sure there is a right or wrong answer.

I always thought the BED 100 data was about early stage NSCLC, so higher stakes on local control because it's a curative setting. When I pick a palliation strategy, its about the tumor anatomy but also the clinical setting. 8/1 is very appropriate. SBRT is also often not inappropriate. If for example you have a fit guy with painful but stable spine oligometastasis from castrate sensitive prostate cancer, you can make a data based argument that 24-28/2 or 30-35/5 is better for the patient than 20/5.

Similar goes for the flipped scenario. We know 35/5 offers good local control in the first year. If your patient has an expected OS of only about a year, what are you gaining by escalating to 50/5 other than risk to OARs? I would use 35/5 a lot in patients with metastatic sarcoma with tumors of the abdomen or of the lung in the reirradiation setting. I just didnt feel that the potential benefit of going to 50 outweighed the risks in a patient who is unlikely to live more than 1-2 years.

Agreed. There is a difference in potential toxicity acceptability threshold for a CURATIVE case vs a metastatic case, even if oligometastatic. This is not only for the toxicity thresholds we think we know (bowel, bladder, etc.) but those we don't (can a pelvic bone take 50Gy in 5 fractions)? Am I going to be OK causing a fracture in a metastatic patient because I wanted to ablate the tumor? I hate use of SABR most of the time, but especially when discussing metastatic patients. Priority is to minimize toxicity while helping the patient more than what would be expected from traditional palliation.

Per the standard LQ equation, there is no time factor. 5 fractions given over 5 weeks has the same BED as 5 fractions given over 1 week.

But, the time factor is real and is roughly accounted for in time adjusted equations.

For something like pCA, which grows slow AF unless it's not an adeno, I doubt that the "real" BED relative to tumor control changes much in going from 1 to 5 weeks. However, regarding the urethral and bladder mucosa, which has rapid cell turnover and proliferation, a week between treatments may markedly improve acute toxicity and even consequential late toxicity.

The data driving BED calcs has a lot of variance. I wouldn't put too much credence in calcs at the limits of clinical practice. (5x10 not the same as 18x3 but both work). For SIB-ing pelvic and retroperitoneal disease between 1.8 and 2.75 Gy/day, I think it's great.

Did you mean 10Gy x 5 or 5Gy x 10 for the bolded? Radically different BEDs. 10Gy x 5 works similarly well for the same reason 24 x 3 would not be necessary - what is dead cannot die even harder. 18x3 is in the flat part of the dose-response curve, while 10 x 5 is closer to the asymptote.

 

[Fpg1245]

I heard even more insane stories from the good ol' 80's when there were no rules except survival of the fittest. By 2000, this had paid (negative) dividends and nowadays, I suspect things are pretty tame at most places. But for those that went thru the dark ages of no mercy, strike first.... never forget, never forgive.

I got a whiff of this and let me tell you. I probably would not have survived

 

[TheWallnerus]

Agreed. There is a difference in potential toxicity acceptability threshold for a CURATIVE case vs a metastatic case, even if oligometastatic. This is not only for the toxicity thresholds we think we know (bowel, bladder, etc.) but those we don't (can a pelvic bone take 50Gy in 5 fractions)? Am I going to be OK causing a fracture in a metastatic patient because I wanted to ablate the tumor? I hate use of SABR most of the time, but especially when discussing metastatic patients. Priority is to minimize toxicity while helping the patient more than what would be expected from traditional palliation.



Did you mean 10Gy x 5 or 5Gy x 10 for the bolded? Radically different BEDs. 10Gy x 5 works similarly well for the same reason 24 x 3 would not be necessary - what is dead cannot die even harder. 18x3 is in the flat part of the dose-response curve, while 10 x 5 is closer to the asymptote.

Regarding the asymptote, not necessarily imho (again will depend on Tpots, alpha/betas, etc).

E.g. say a tumor has a D-zero of 2 Gy (sort of radiosensitive). Treating a billion cell tumor mass (and that may be overestimate for small-ish targets...but anyways)...

10Gy x 5 = ((0.37^5)^5)*1E9 = 0.016 = 98.4% LC probability
18Gy x 3 = ((0.37^9)^3)*1E9 = 0.002 = 99.8% LC probability

IRL, it would seem like "both work" the same (and they essentially would, for a D-zero equals 2 Gy tumor), no significant "asymptotic flirtation" w/ the 50Gy/5fx. The D-zero of some head/neck cancers is probably close to 2 Gy; the D-zero of prostate cancer is certainly more than 2 Gy.

 

[communitydoc13]

Did you mean 10Gy x 5 or 5Gy x 10 for the bolded? Radically different BEDs. 10Gy x 5 works similarly well for the same reason 24 x 3 would not be necessary - what is dead cannot die even harder. 18x3 is in the flat part of the dose-response curve, while 10 x 5 is closer to the asymptote.

I meant 10 Gy x 5 and I agree with your reasoning.

But I also don't think applying an a/b for very hypofractionated regimens is something that one should have a lot of confidence in. There are lots of reasonable regimens that work, and in my opinion, the slightly less hypofractionated ones tend to have a better side effect profile (lower incidence of things like symptomatic brain necrosis or vertebral body collapse).

Think 9Gy x 3, 12 Gy x 2 or 18Gy x 1 for spine mets or fractionated SBRT regimens for brain mets.