Rad Onc Twitter

[Fpg1245]

---

Members don't see this ad.

This exchange is precisely why clinical oncology should be the future.

 

[jondunn]

 

[TheWallnerus]

This is a new one

Crushing those mad industry payment gains bro

 

[thecarbonionangle]

Seeing that picture i cant help to hear the cash register “chaching”. Just need all the other spaceoar grifters in pic from the other thread listing them and you got a party baby

 

[jondunn]

 

[medgator]

Retirement?

 

[Palex80]

Retirement?

Go get a PSA test done, maybe you need prostate SBRT yourself?

 

[thecarbonionangle]

Go get a PSA test done, maybe you need prostate SBRT yourself?

Is the gator so old to be having a weak stream already?

 

[deleted1111261]

He’s having a hard time even putting out birthday candles with those dribbles

 

[communitydoc13]

Here is pencil beam CSI 30 Gy / 10 fractions with 5 mm robustness. I'm thinking two things.
1. If we go down to 3 mm robustness is that sufficient? The marrow would be more spared this way.
2. What isodose spares marrow? The 1500 cGy line is less than midway through the T and L-spines. The 300 cGy line goes through ~80-90% of the bone.

View attachment 357113

I'm one of the biggest critics of protons. I do not believe they are a tool for dose escalation and I do not believe that the dosimetry is well characterized....I think they are frankly dangerous when a critical OAR is next to target.

But, you are not getting a plan like this with VMAT (maybe the worst technique for marrow sparing as at least with PA photon plans you are getting nothing to iliac bones). It is also OK if there are some 140% hot spots in this plan.

When the dose is low and the low dose bath matters (CSI and peds/young person lymphoma) protons have value. I would definitely send out the rare person who could benefit from this to a proton center.

The docs involved in the trial may just have felt that 30 Gy/10 VMAT CSI not that ethical. (Also 30 Gy/10 PA will make you sick, give big heart dose and not pay very well).

 

[Palex80]

I'm one of the biggest critics of protons. I do not believe they are a tool for dose escalation and I do not believe that the dosimetry is well characterized....I think they are frankly dangerous when a critical OAR is next to target.

But, you are not getting a plan like this with VMAT (maybe the worst technique for marrow sparing as at least with PA photon plans you are getting nothing to iliac bones). It is also OK if there are some 140% hot spots in this plan.

When the dose is low and the low dose bath matters (CSI and peds/young person lymphoma) protons have value. I would definitely send out the rare person who could benefit from this to a proton center.

The docs involved in the trial may just have felt that 30 Gy/10 VMAT CSI not that ethical. (Also 30 Gy/10 PA will make you sick, give big heart dose and not pay very well).

VMAT-CSI does not have to be a 360° rotational technique. You can do partial arcs, thus restricting your dose to structures lateral to the target.

(This is a paediatric patient, which is why the PTV includes the vertrebral body too, imagine the same technique with the PTV only encompassing the spinal cord)

 

[communitydoc13]

VMAT-CSI does not have to be a 360° rotational technique. You can do partial arcs, thus restricting your dose to structures lateral to the target.

View attachment 357180
(This is a paediatric patient, which is why the PTV includes the vertrebral body too, imagine the same technique with the PTV only encompassing the spinal cord)

Sweet.

What's that blue isodose paint? Just making sure its not 85%, 80% or even 50%, cause that 50% iso on the proton plan (admitting there may be a 140% spot somewhere in close proximity) is damn close to the 100% iso.

 

[jondunn]

VMAT-CSI does not have to be a 360° rotational technique. You can do partial arcs, thus restricting your dose to structures lateral to the target.

View attachment 357180
(This is a paediatric patient, which is why the PTV includes the vertrebral body too, imagine the same technique with the PTV only encompassing the spinal cord)

 

[theradiator]

Interesting especially because Washington University has protons

 

[jondunn]

I think WashU does things correctly and well and ethically. I respect their department quite a bit

 

[medgator]

I think WashU does things correctly and well and ethically. I respect their department quite a bit

Sure thing, "big rad Onc"

You're like the resident Dr K Olivier on this forum lately, JD

 

[Palex80]

Sweet.

What's that blue isodose paint? Just making sure its not 85%, 80% or even 50%, cause that 50% iso on the proton plan (admitting there may be a 140% spot somewhere in close proximity) is damn close to the 100% iso.

That is the 9 Gy /23.4 Gy (standard risk medulloblastoma) isodose line = 38.4%

 

[TheWallnerus]

Look at Palex80 plan

I am going to guess he did not contour CTV anteriorly into the vertebral bodies. I would not consider bone part of the subclinical-at-risk region for disease in the CNS/CSF (are we treating the craniospinal axis, or the craniospinal axis plus widespread and oddly localized bone mets to the skull and all vertebral bodies as well?). But, he must "project" dose anteriorly that way due to the "beam angles" all coming in posterior-ish. It's just physics and limitations of photons.

But protons don't have that limitation. Entering posteriorly, the planner can stop the proton beam anteriorly any place he chooses. So why do proton users include all the vertebral bone in the CTV and stop the proton beam so far anteriorly past the CNS/CSF? It's needless and/or thoughtless irradiation?

 

[NotMattSpraker]

Look at Palex80 plan

I am going to guess he did not contour CTV anteriorly into the vertebral bodies. I would not consider bone part of the subclinical-at-risk region for disease in the CNS/CSF (are we treating the craniospinal axis, or the craniospinal axis plus widespread and oddly localized bone mets to the skull and all vertebral bodies as well?). But, he must "project" dose anteriorly that way due to the "beam angles" all coming in posterior-ish. It's just physics and limitations of photons.

But protons don't have that limitation. Entering posteriorly, the planner can stop the proton beam anteriorly any place he chooses. So why do proton users include all the vertebral bone in the CTV and stop the proton beam so far anteriorly past the CNS/CSF? It's needless and/or thoughtless irradiation?

Not sure if I'm answering your question, but there is range uncertainty that must be added to the distal end of the beam as a "PTV-like" expansion to allow for a robust plan. Also, in the area of the diaphragms, many centers do a 4D and add in range to account for density changes with breathing. You can see how that beam the dose just takes off anteriorly in the lungs. Finally, as others have said, I am kind of scared of the proton TPS. I do not like it when my beam ends in critical structures like the cord or esophagus, so putting in bone is better IMO.

Anecdotally, they do try to spare anterior VBs in adults and cover something like 80% in kids due to wanting to limit growth abnormalities. I do not do this ever, so this just based on what I've seen in rounds.

 

[Palex80]

Look at Palex80 plan

I am going to guess he did not contour CTV anteriorly into the vertebral bodies. I would not consider bone part of the subclinical-at-risk region for disease in the CNS/CSF (are we treating the craniospinal axis, or the craniospinal axis plus widespread and oddly localized bone mets to the skull and all vertebral bodies as well?). But, he must "project" dose anteriorly that way due to the "beam angles" all coming in posterior-ish. It's just physics and limitations of photons.

It's a pediatric patient, still quite young. We had to treat the vertebral bodies to a dose of around 20 Gy to avoid and deformation from happening during growth (lordosis). There is actually one CTV in that plan (the spinal canal + nerve roots) and there's an additional structure that assures the vertebral body would receive 20 Gy.
But since that patient is getting only 23.4 Gy to the spinal canal, you do not see much of a difference on that plan.
Would it have been a high-risk medulloblastoma, getting 36 Gy, you would see a greater difference between dose delivered to vertebral bodies and dose delivered to the spinal canal.

I have to admit, I am skeptical if we need to actually treat the entire vertebral body with 20 Gy to avoid these deformations in pediatric patients, when we use modern techniques. But it's the way it was written in the trial protocol and we treat most of these patients on trial.

But protons don't have that limitation. Entering posteriorly, the planner can stop the proton beam anteriorly any place he chooses. So why do proton users include all the vertebral bone in the CTV and stop the proton beam so far anteriorly past the CNS/CSF? It's needless and/or thoughtless irradiation?

That is completely true and would only be justified if that was a pediatric patient. Even then though, you should be seeing two dose levels. One around the spinal canal and one around the vertebral body.

 

[TheWallnerus]

It's a pediatric patient, still quite young. We had to treat the vertebral bodies to a dose of around 20 Gy to avoid and deformation from happening during growth (lordosis). There is actually one CTV in that plan (the spinal canal + nerve roots) and there's an additional structure that assures the vertebral body would receive 20 Gy.
But since that patient is getting only 23.4 Gy to the spinal canal, you do not see much of a difference on that plan.
Would it have been a high-risk medulloblastoma, getting 36 Gy, you would see a greater difference between dose delivered to vertebral bodies and dose delivered to the spinal canal.

I have to admit, I am skeptical if we need to actually treat the entire vertebral body with 20 Gy to avoid these deformations in pediatric patients, when we use modern techniques. But it's the way it was written in the trial protocol and we treat most of these patients on trial.


That is completely true and would only be justified if that was a pediatric patient. Even then though, you should be seeing two dose levels. One around the spinal canal and one around the vertebral body.

Totally forgot to think along pediatric lines (as I’m wont to do having never treated a peds case my entire career). On one hand, makes sense to dose the vertebral bodies. But gosh this just reminds me how medieval/antediluvian radiation occasionally/rarely is: because the child is getting CSI, we have to uniformly “torch” the uninvolved, normal vertebral bone-making cells of the child so the child doesn’t grow funny. Re: your thoughts on skepticism (“electively” irradiate the VBs or no), would be a great trial but for a whole host of reasons I see why that trial has never ran.

Not sure if I'm answering your question, but there is range uncertainty that must be added to the distal end of the beam as a "PTV-like" expansion to allow for a robust plan. Also, in the area of the diaphragms, many centers do a 4D and add in range to account for density changes with breathing. You can see how that beam the dose just takes off anteriorly in the lungs. Finally, as others have said, I am kind of scared of the proton TPS. I do not like it when my beam ends in critical structures like the cord or esophagus, so putting in bone is better IMO.

Anecdotally, they do try to spare anterior VBs in adults and cover something like 80% in kids due to wanting to limit growth abnormalities. I do not do this ever, so this just based on what I've seen in rounds.

That seems like a 2-3cm expansion margin though anteriorly. I’d understand maybe a half cm or so. You would not expand anteriorly this much in adult CSI w protons would you due to “robustness”? That would be measurable toxicity inducing robustness?

 

[RickyScott]

Totally forgot to think along pediatric lines (as I’m wont to do having never treated a peds case my entire career). On one hand, makes sense to dose the vertebral bodies. But gosh this just reminds me how medieval/antediluvian radiation occasionally/rarely is: because the child is getting CSI, we have to uniformly “torch” the uninvolved, normal vertebral bone-making cells of the child so the child doesn’t grow funny. Re: your thoughts on skepticism (“electively” irradiate the VBs or no), would be a great trial but for a whole host of reasons I see why that trial has never ran.

That seems like a 2-3cm expansion margin though anteriorly. I’d understand maybe a half cm or so. You would not expand anteriorly this much in adult CSI w protons would you due to “robustness”? That would be measurable toxicity inducing robustness?

The couple cases I had with vmat to the canal with a 5 mm margin did not have problems with counts or gi toxicity.

 

[thecarbonionangle]

Look at Palex80 plan

I am going to guess he did not contour CTV anteriorly into the vertebral bodies. I would not consider bone part of the subclinical-at-risk region for disease in the CNS/CSF (are we treating the craniospinal axis, or the craniospinal axis plus widespread and oddly localized bone mets to the skull and all vertebral bodies as well?). But, he must "project" dose anteriorly that way due to the "beam angles" all coming in posterior-ish. It's just physics and limitations of photons.

But protons don't have that limitation. Entering posteriorly, the planner can stop the proton beam anteriorly any place he chooses. So why do proton users include all the vertebral bone in the CTV and stop the proton beam so far anteriorly past the CNS/CSF? It's needless and/or thoughtless irradiation?

My understanding: Beam goes into heart in area of the lungs because of decreased stopping power. This is why in lungs it is not always the greatest modality to use. Always a case by case situation

 

[thecarbonionangle]

Totally forgot to think along pediatric lines (as I’m wont to do having never treated a peds case my entire career). On one hand, makes sense to dose the vertebral bodies. But gosh this just reminds me how medieval/antediluvian radiation occasionally/rarely is: because the child is getting CSI, we have to uniformly “torch” the uninvolved, normal vertebral bone-making cells of the child so the child doesn’t grow funny. Re: your thoughts on skepticism (“electively” irradiate the VBs or no), would be a great trial but for a whole host of reasons I see why that trial has never ran.

That seems like a 2-3cm expansion margin though anteriorly. I’d understand maybe a half cm or so. You would not expand anteriorly this much in adult CSI w protons would you due to “robustness”? That would be measurable toxicity inducing robustness?

There is an ongoing peds trial just treating the canal with margin with protons vs covering the whole VB

 

[jondunn]

Sure thing, "big rad Onc"

You're like the resident Dr K Olivier on this forum lately, JD

yeah saying a department does research and clinical care well is something you simply don't like, because neither is important to you.

I got it!

plenty of places that I criticize non stop, but it's not enough for Dr. Gator.

Gator is the master of SDN, I guess.

 

[TheWallnerus]

The couple cases I had with vmat to the canal with a 5 mm margin did not have problems with counts or gi toxicity.

An approach like this, at palliative doses, is going to be exceedingly difficult for protons to beat

 

[theradiator]

An approach like this, at palliative doses, is going to be exceedingly difficult for protons to beat

To summarize, perhaps protons as a modality gave our field the bravery to even tackle leptomeningeal metastases. Now that proof of principle of activity has been established, VMAT has a number of implementation advantages including lower cost, greater availability and greater dose certainty to enable safe reduction in PTV margins for those few patients that would potentially benefit.

 

[RickyScott]

An approach like this, at palliative doses, is going to be exceedingly difficult for protons to beat

These were palliative with some gaps. No feathering etc .

 

[communitydoc13]

An approach like this, at palliative doses, is going to be exceedingly difficult for protons to beat

Yeah, bone marrow sparing seems to be the thing where I can see protons still coming out on top here. They have stopped beams right at the front of the thecal sac in kids.

A Multi-institutional Comparative Analysis of Proton and Photon Therapy-Induced Hematologic Toxicity in Patients With Medulloblastoma - PubMed

Patients who receive CSI using proton therapy experience significantly decreased hematologic toxicity compared with those receiving photon therapy.

pubmed.ncbi.nlm.nih.gov

Of course lymphopenia has not been well correlated with clinical outcomes despite the interest in this by proton acolytes.

 

[TheWallnerus]

These were palliative with some gaps. No feathering etc .

I intentionally overlap the fields from the various isos by a cm or 1.5 cm. The algorithm “feathers” the overlaps perfectly. This way it’s just treat, move patient to next iso and treat, and next iso and treat if necessary. But usually I use four isos. Head. Cervically, I get zero anterior dose due to beam choice. Then thoracic. The L spine. The isos are set multiples of 5cm apart for easier “shifting math.” The dose coverage is gapless, uniform. It’s so neat imho.

 

[taserlaser]

I intentionally overlap the fields from the various isos by a cm or 1.5 cm. The algorithm “feathers” the overlaps perfectly. This way it’s just treat, move patient to next iso and treat, and next iso and treat if necessary. But usually I use four isos. Head. Cervically, I get zero anterior dose due to beam choice. Then thoracic. The L spine. The isos are set multiples of 5cm apart for easier “shifting math.” The dose coverage is gapless, uniform. It’s so neat imho.

We overlap the fields as well and ramp up the dose in each field in the overlap region. A sup/inf positional error in any single field will result in very minimal change to the sum dose across the cord in this way, and is quite robust.

If you shift blue or green (the fields) in either direction across the X axis, the sum dose is minimally perturbed. Hooray

 

[Neuronix]

We overlap the fields as well and ramp up the dose in each field in the overlap region. A sup/inf positional error in any single field will result in very minimal change to the sum dose across the cord in this way, and is quite robust.

If you shift blue or green (the fields) in either direction across the X axis, the sum dose is minimally perturbed. Hooray

IMPT does it basically the same way, except instead of using MLC blocking to feather dose it uses spot fluence to feather dose at the edges of the fields.

 

[jondunn]

 

[RickyScott]

So they must be deploying if in a lot of conventionally fractionated xrt.

 

[RickyScott]

We overlap the fields as well and ramp up the dose in each field in the overlap region. A sup/inf positional error in any single field will result in very minimal change to the sum dose across the cord in this way, and is quite robust.

If you shift blue or green (the fields) in either direction across the X axis, the sum dose is minimally perturbed. Hooray

Very clever. Kind of annoyed I didn’t think of it.

 

[thesauce]

Not sure if I'm answering your question, but there is range uncertainty that must be added to the distal end of the beam as a "PTV-like" expansion to allow for a robust plan. Also, in the area of the diaphragms, many centers do a 4D and add in range to account for density changes with breathing. You can see how that beam the dose just takes off anteriorly in the lungs. Finally, as others have said, I am kind of scared of the proton TPS. I do not like it when my beam ends in critical structures like the cord or esophagus, so putting in bone is better IMO.

Anecdotally, they do try to spare anterior VBs in adults and cover something like 80% in kids due to wanting to limit growth abnormalities. I do not do this ever, so this just based on what I've seen in rounds.

I knew there was a range uncertainty, but I didn’t know it was 1+ centimeters. That’s nuts..

 

[FindMeOnTheLinks]

I knew there was a range uncertainty, but I didn’t know it was 1+ centimeters. That’s nuts..

yeah…typically estimated to be ~3.5% of the range and then add a mm or two. So if you’re treating at 20cm depth, it’s around 8mm

 

[RickyScott]

yeah…typically estimated to be ~3.5% of the range and then add a mm or two. So if you’re treating at 20cm depth, it’s around 8mm

Not good for lung/mediastinum?

 

[thecarbonionangle]

yeah…typically estimated to be ~3.5% of the range and then add a mm or two. So if you’re treating at 20cm depth, it’s around 8mm

Which is not so different than what people use in pelvis/thorax PTV where 5-8mm i have seen used. Especially in “dont wanna miss” crowd.

 

[thecarbonionangle]

Not good for lung/mediastinum?

depends on case

 

[FindMeOnTheLinks]

Not good for lung/mediastinum?

I think can get good dosimetry for peripheral lung tumors to avoid low dose bath to the lung and minimize the V20. You might get a little bit more high dose to the lung and chest wall since it is proximal in the beam path…. And then not only do you have range uncertainty you also have tissue density uncertainty from the significant air-tissue interface in the lung. Mediastinum/central lung, I think would be more tricky

Other issue is pencil beam scanning is not very robust to tumor motion so you could only do it with double scattering. Also you start to lose the distal RBE advantage once you get into larger dose per fraction (ie SBRT).

 

[Lamount]

yeah…typically estimated to be ~3.5% of the range and then add a mm or two. So if you’re treating at 20cm depth, it’s around 8mm

To be fair, this estimate is sans Monte Carlo, and not using dual energy CT. Probably closer to 2%

 

[TheWallnerus]

All the discussions above lend credence to a general idea I have that protons are not as precise as photons. That is to say, the ratio of the prescription isovolume to the PTV is greater in protons than photons. They are a kind of step backward in that regard. That would bother me as I have spent a whole career trying to get that ratio as close as possible to one in every single patient’s case. When you get into protons the first time, is it tough to let this notion go?

 

[Palex80]

When you get into protons the first time, is it tough to let this notion go?

Once you get protons, you never want photons.

 

[RadOncDoc21]

Once you get protons, you never want photons.

Buyer’s remorse?

 

[TheWallnerus]

Once you get protons, you never want photons.

Ha. Maybe. They mesmerize a lot of people: rad oncs, deans of med schools, rad onc companies, financiers, etc. Usually in medicine we go “all in” on things with clear upsides. In protons, it was “there are some trade offs.” I can see the trade offs on screen and I bet proton users see the trade offs up close and personal in clinic. (I think I have relayed the true story before where at the local academic proton center they sometimes have to switch breast patients from proton to photon due to skin toxicity.) We are spending $100 million per center and bankrupting rad onc for trade offs? “Hey must be the money” as Nelly would say.

 

[Fpg1245]

Ha. Maybe. They mesmerize a lot of people: rad oncs, deans of med schools, rad onc companies, financiers, etc. Usually in medicine we go “all in” on things with clear upsides. In protons, it was “there are some trade offs.” I can see the trade offs on screen and I bet proton users see the trade offs up close and personal in clinic. (I think I have relayed the true story before where at the local academic proton center they sometimes have to switch breast patients from proton to photon due to skin toxicity.) We are spending $100 million per center and bankrupting rad onc for trade offs? “Hey must be the money” as Nelly would say.

Although one would argue rad onc is already bankrupt scientifically, possibly morally, as well as financially. Protons just speed the process up…**** it I’m all in because god knows there’s nothing better coming along.

 

[thecarbonionangle]

Although one would argue rad onc is already bankrupt scientifically, possibly morally, as well as financially. Protons just speed the process up…**** it I’m all in because god knows there’s nothing better coming along.

What i hear from protonists is “next big thing” is arc proton therapy (spread our LET) and FLASH (proton machines currently only are only ones that can deliver standard and flash rates at same time)

 

[Mandelin Rain]

Although one would argue rad onc is already bankrupt scientifically, possibly morally, as well as financially. Protons just speed the process up…**** it I’m all in because god knows there’s nothing better coming along.

 

[jondunn]

What i hear from protonists is “next big thing” is arc proton therapy (spread our LET) and FLASH (proton machines currently only are only ones that can deliver standard and flash rates at same time)

You sure do hangout in the right swamps!