Liver SBRT and being rural

[Ray D. Ayshun]

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I am able to do liver SBRT safely. in turn, that makes me the only person in my neck of the woods that can treat a solitary liver lesion definitively (no surgeon here would do this, and no IR). I was referred a patient with HCC by the local med onc. The lesion was originally thought to be a lung met. The patient is 80 and relatively healthy, but doesn't want surgery, and isn't really interested in driving somewhere to meet with interventional radiology, or for that matter a hepatolgist. Wondering how many of you would go ahead and treat. She's childs pugh A and the lesion is well away from luminal GI, so a chip shot as it were, but still, this has always been a multiD thing to start.

 

[ramsesthenice]

I am able to do liver SBRT safely. in turn, that makes me the only person in my neck of the woods that can treat a solitary liver lesion definitively (no surgeon here would do this, and no IR). I was referred a patient with HCC by the local med onc. The lesion was originally thought to be a lung met. The patient is 80 and relatively healthy, but doesn't want surgery, and isn't really interested in driving somewhere to meet with interventional radiology, or for that matter a hepatolgist. Wondering how many of you would go ahead and treat. She's childs pugh A and the lesion is well away from luminal GI, so a chip shot as it were, but still, this has always been a multiD thing to start.

Unless you think you might burn an important bridge I would treat. Assuming a reputable radiologist has made the diagnosis. Too old to be listed so at this point it’s a matter of her preference for local therapy and sounds like she has already made up her mind.

 

[Ray D. Ayshun]

Unless you think you might burn an important bridge I would treat. Assuming a reputable radiologist has made the diagnosis. Too old to be listed so at this point it’s a matter of her preference for local therapy and sounds like she has already made up her mind.

diagnosis made with biopsy as it was first characterized with only contrasted CT, and thought to be related to history of NSCLC.

thanks, i laid out the options and normal process, and she has time to think as i want a liver MRI w/wo before doing a sim.

 

[Palex80]

Liver MRI makes sense. Do you have a biopsy of the healthy liver too or only of the lesion?

 

[Ray D. Ayshun]

Liver MRI makes sense. Do you have a biopsy of the healthy liver too or only of the lesion?

Only the lesion, why?

 

[Palex80]

Only the lesion, why?

In HCC it's nice to know what the rest of the liver looks like. Our hepatologists generally make a biopsy of the normal liver to rule out any liver pathology when they perform biopsies for HCC. I presume the lesion in small and you will not run into any troubles meeting liver constraints, right?

 

[Ray D. Ayshun]

In HCC it's nice to know what the rest of the liver looks like. Our hepatologists generally make a biopsy of the normal liver to rule out any liver pathology when they perform biopsies for HCC. I presume the lesion in small and you will not run into any troubles meeting liver constraints, right?

Yes, very straightforward 3 cm lesion in ant/sup segment 8.

 

[RadRadRad]

Agree With other posts. Can’t see that transplant is option for 80 year old and she doesn’t want surgery/resection

PMH data for sbrt is compelling especially if you can give higher dose. She is childs Pugh a so should be well tolerated.

I get that the typical pathway for these patients is to send them to a majortransplant center for multi-d opinion but don’t think it’s required in this case.

 

[Palex80]

Yes, very straightforward 3 cm lesion in ant/sup segment 8.

Treat it. Your med onc will love you and will send more.
😉

 

[Ray D. Ayshun]

Agree With other posts. Can’t see that transplant is option for 80 year old and she doesn’t want surgery/resection

PMH data for sbrt is compelling especially if you can give higher dose. She is childs Pugh a so should be well tolerated.

I get that the typical pathway for these patients is to send them to a majortransplant center for multi-d opinion but don’t think it’s required in this case.

The question is kinda also, how much should I push IR modalities? My bias is there's no difference wrt local control, which is more or less borne out in well done reviews, in particular the michigan data, where sbrt would be better in the present case. OTOH, it still seems like the NCCN would push RFA or embo before SBRT if possible.

 

[RadRadRad]

Yes
My bias is also that sbrt is comparable to other non surgical modalities. I’ve personally done sbrt and y90 (favoring sbrt for 1-2 lesions and y90 for multifocal disease). I have not found that y90 has better respond rate / local control
Also sbrt is definitely better tolerated and noninvasive, both pluses for an 80 year old

 

[metview]

For educational purposes: How would you treat? Dose (50 Gy in 5 fractions)? 4D-CT? ABC, abdominal compression device, or free breathing with larger ITVs? Fuse in the diagnostic MRI for contouring?

Thanks

 

[Ray D. Ayshun]

For educational purposes: How would you treat? Dose (50 Gy in 5 fractions)? 4D-CT? ABC, abdominal compression device, or free breathing with larger ITVs? Fuse in the diagnostic MRI for contouring?

Thanks

This one yes. I described my approach in pm, but happy to repeat, and hear others'. I like rtog 1112 approach. 50 to itv and 40 to ptv in 5 fx. Free breathing if possible, but if 4d shows too much motion, then some sort of management. We did a triphasic contrasted sim in training, but here I'll just do con and no con and contour on all scans, along with a fused diagnostic mri. Expansions to ptv maybe slightly asymmetric in the sup inf planes depending on tumor size. No fiducials, so daily cbct, align to nearby liver contours. Use rtog 1112 constraints. If unable to meet will go as low as 6 x 5, or else 5 gy x 10.

Oh, and no food 2-3 hrs before. Have seen the stomach mess things up. Have also seen the gallbladder mess things up too, which, oddly, was fixed by having the patient eat a burger for lunch before treatment at the end of the day.

 

[scarbrtj]

This one yes. I described my approach in pm, but happy to repeat, and hear others'. I like rtog 1112 approach. 50 to itv and 40 to ptv in 5 fx. Free breathing if possible, but if 4d shows too much motion, then some sort of management. We did a triphasic contrasted sim in training, but here I'll just do con and no con and contour on all scans, along with a fused diagnostic mri. Expansions to ptv maybe slightly asymmetric in the sup inf planes depending on tumor size. No fiducials, so daily cbct, align to nearby liver contours. Use rtog 1112 constraints. If unable to meet will go as low as 6 x 5, or else 5 gy x 10.

Oh, and no food 2-3 hrs before. Have seen the stomach mess things up. Have also seen the gallbladder mess things up too, which, oddly, was fixed by having the patient eat a burger for lunch before treatment at the end of the day.

If anyone did something significantly different than this you'd wonder "Why?" I really run hard toward free breathing (FB) as much as possible. I capture multiple free breathing scans, fuse them, and create my ITV that way. Most of us don't have gated CBCT so this makes sense (ie match tx room to sim), to me, to do SBRTs this way and after a decade of doing FB I'm not unhappy with it. I will admit there's *much* room for ITV shrinkage w/ robust motion approach. A 3cm tumor has a volume of 15cc and the PTV with free breathing can approach 200cc. This is where MRgRT could be a dominant force, but even then when constraints are met (for a 3cm GTV) a ~30-60cc PTV w/ motion control vs ~200cc without may not be clinically important in the liver. Plus I'm not sure RT will work its way into the 2nd promised land by shrinking PTVs for liver cases but topic for another time.

 

[seper]

Rare case, but agree: skip transpalnt referral and 50/5

 

[ramsesthenice]

If anyone did something significantly different than this you'd wonder "Why?" I really run hard toward free breathing (FB) as much as possible. I capture multiple free breathing scans, fuse them, and create my ITV that way. Most of us don't have gated CBCT so this makes sense (ie match tx room to sim), to me, to do SBRTs this way and after a decade of doing FB I'm not unhappy with it. I will admit there's *much* room for ITV shrinkage w/ robust motion approach. A 3cm tumor has a volume of 15cc and the PTV with free breathing can approach 200cc. This is where MRgRT could be a dominant force, but even then when constraints are met (for a 3cm GTV) a ~30-60cc PTV w/ motion control vs ~200cc without may not be clinically important in the liver. Plus I'm not sure RT will work its way into the 2nd promised land by shrinking PTVs for liver cases but topic for another time.

I do a lot of liver SBRT (treat 4-5 patients per month). I evaluate everyone with a 4D but don’t end up using abdominal compression that often. It takes a good bit of pressure to drastically change the PTV volume for a lot of folks and the usual specimens for HCC are not really built for the squeeze. Can also end up pushing luminal structures closer to the PTV.

50/5 is a common course. I usually go with 45/3 but no difference in control that I am aware of.

 

[Palex80]

What isodose are you prescribing the 50/5 to? Do you have any goals for maximum dose in the GTV/ITV?

 

[GI_RadOnc]

I use 50 Gy / 5 fractions to cover the PTV at 95% coverage for a lesion like this. MRgRT makes this a chip shot; but agree, one would be hard pressed to create a trial to show any benefit of MRgRT versus standard linear acceleration. Interestingly, in a PMH/Michigan paper that came out; breath hold versus other motion management was associated with improved local control... but I wouldn't use this one analysis to preclude offering a definitive therapy to a patient who isn't going to go far!

Long term outcomes of stereotactic body radiation therapy for hepatocellular carcinoma without macrovascular invasionEur J Cancer 2020 Jul;134:41-51. doi: 10.1016/j.ejca.2020.04.024. Epub 2020 May 24.

 

[evilbooyaa]

Most have answered uniformly, but to add my two cents:

1) Get a liver MRI if you haven't (didn't see this mentioned in your posts). Multifocal HCC is unfortunately very real. If MRI is clean besides the known lesion, then blast away. If other suspicious areas that end up being confirmed, patient may be better served with either something like Y-90 or consideration of TKI.
2) If you feel confident in being able to line up to a non-con CT based on liver anatomy, then OK, but this is one site that I frequently want fiducials.
3) 50/5 if feasible and meeting constraints. 54/3 also reasonable per Colorado experience. Would not go lower than 40/5 to PTV if at all possible. Sometimes lesions close to duodenum or something need to go lower but hopefully that's not the case.
3) I agree with avoiding compression as luminal organs get mushed into it. 4DCT with MRI fusion on free breathing very reasonable.

SBRT for HCC is very effective compared to RFA - for lesions > 3cm in size, control may be better with SBRT than RFA.

Outcomes After Stereotactic Body Radiotherapy or Radiofrequency Ablation for Hepatocellular Carcinoma - PubMed

Both RFA and SBRT are effective local treatment options for inoperable HCC. Although these data are retrospective, SBRT appears to be a reasonable first-line treatment of inoperable, larger HCC.

pubmed.ncbi.nlm.nih.gov

Retrospective analysis of stereotactic body radiation therapy efficacy over radiofrequency ablation for hepatocellular carcinoma - PubMed

SBRT appears to be an effective alternative treatment for HCC when RFA is not feasible due to tumor location or size.

pubmed.ncbi.nlm.nih.gov

Comparative clinical trials ongoing:

ClinicalTrials.gov

clinicaltrials.gov

 

[ramsesthenice]

Most have answered uniformly, but to add my two cents:

1) Get a liver MRI if you haven't (didn't see this mentioned in your posts). Multifocal HCC is unfortunately very real. If MRI is clean besides the known lesion, then blast away. If other suspicious areas that end up being confirmed, patient may be better served with either something like Y-90 or consideration of TKI.
2) If you feel confident in being able to line up to a non-con CT based on liver anatomy, then OK, but this is one site that I frequently want fiducials.
3) 50/5 if feasible and meeting constraints. 54/3 also reasonable per Colorado experience. Would not go lower than 40/5 to PTV if at all possible. Sometimes lesions close to duodenum or something need to go lower but hopefully that's not the case.
3) I agree with avoiding compression as luminal organs get mushed into it. 4DCT with MRI fusion on free breathing very reasonable.

SBRT for HCC is very effective compared to RFA - for lesions > 3cm in size, control may be better with SBRT than RFA.

Outcomes After Stereotactic Body Radiotherapy or Radiofrequency Ablation for Hepatocellular Carcinoma - PubMed

Both RFA and SBRT are effective local treatment options for inoperable HCC. Although these data are retrospective, SBRT appears to be a reasonable first-line treatment of inoperable, larger HCC.

pubmed.ncbi.nlm.nih.gov

Retrospective analysis of stereotactic body radiation therapy efficacy over radiofrequency ablation for hepatocellular carcinoma - PubMed

SBRT appears to be an effective alternative treatment for HCC when RFA is not feasible due to tumor location or size.

pubmed.ncbi.nlm.nih.gov

Comparative clinical trials ongoing:

ClinicalTrials.gov

clinicaltrials.gov

Lipiadol is by far the best fiducial you could use. I treat so many of these because our oncologists have completely bought into 2-hit therapy for patients who are not going to surgery (TACE -> SBRT). Decent retrospective data showing better LC than either alone (which makes sense). Anyway, these things glow on KV CBCT when they are full of lipiadol.

A word of caution of fiducials...depending on your imager they can be harder to align to than you might think (if there is a good bit of motion). Its tempting to want to align to the most crisp fiducial image but if you are treating an ITV thats probably not optimal. Need to align to the "top" of the fiducials to catch maximal displacement.

 

[OTN]

Absolutely treat. IMO surgery > SBRT > all other local modalities. 50 in 5.

MRI necessary to r/o other lesions and to target.

Agree that fiducials can be challenging. I like to use MiM to deformably fuse the MRI to the planning CT. Belt rather than plate compression on the CT sim to reduce deformation of the liver.

 

[metview]

For those that use 4D-CT and no fiducials, a couple of questions:

1. Do you take into consideration timing of IV contrast so tumor is scanned during arterial phase? If so, how?
2. Do you contour on all phases or just 0% and 50%/60%?

Thanks

 

[OTN]

For those that use 4D-CT and no fiducials, a couple of questions:

1. Do you take into consideration timing of IV contrast so tumor is scanned during arterial phase? If so, how?
2. Do you contour on all phases or just 0% and 50%/60%?

Thanks

We pulled all of our radiology scan parameters from the local huge radiology group, and they've been super helpful in setting up our protocols. As a result, I can't give you details, but I can look into it.

I contour on all ten phases. Doesn't add that much extra work and makes me feel much better that I'm not missing anything.

 

[Krukenberg]

We pulled all of our radiology scan parameters from the local huge radiology group, and they've been super helpful in setting up our protocols. As a result, I can't give you details, but I can look into it.

I contour on all ten phases. Doesn't add that much extra work and makes me feel much better that I'm not missing anything.

do you acquire your 4DCT through the arterial phase? Some tumors are visible on non contrast 4DCT but in my experience most are not

 

[OTN]

do you acquire your 4DCT through the arterial phase? Some tumors are visible on non contrast 4DCT but in my experience most are not

Agree that most are not- that's why MRI fusion is so critical. Sure is nice when you have easily identified hypodensities on CT, but by no means the norm.

 

[Ray D. Ayshun]

you can protocol to do triphasic: arterial, venous and washout. Something like 15-30 sec, 75-90, and 180 after infusion. Can do bolus tracking as well if youre scanner will do it.

 

[ramsesthenice]

Agree that most are not- that's why MRI fusion is so critical. Sure is nice when you have easily identified hypodensities on CT, but by no means the norm.

HCCs are notoriously hard to see on CT even with contrast. Even the ones that do only partially show up on CT. Completely agree with MR fusion.

I use respiratory gating so sequences vary per patient but in non gated patients I just do 0, 100, and exp BH as long as the contours look logical. If you have weird motion and the contours don’t look contiguous on the different phases I will add more (occasionally you will see crescent shaped motion patterns).

 

[Krukenberg]

Agree that most are not- that's why MRI fusion is so critical. Sure is nice when you have easily identified hypodensities on CT, but by no means the norm.

totally agree MR fusion is necessary and we do it too. Just wondering how you contour the tumor on each phase of the 4DCT if you can’t see the actual mass. MRI abdomen is generally only acquired with a breath hold.
We do DIBH whenever possible. If not then we do 4DCT but you have to infer motion of the tumor from amount of fiducial movement. If no fiducials then it gets tricky...

 

[Ray D. Ayshun]

totally agree MR fusion is necessary and we do it too. Just wondering how you contour the tumor on each phase of the 4DCT if you can’t see the actual mass. MRI abdomen is generally only acquired with a breath hold.
We do DIBH whenever possible. If not then we do 4DCT but you have to infer motion of the tumor from amount of fiducial movement. If no fiducials then it gets tricky...

This is the added benefit of doing a triphasic sime in my estimation. You can generate an ITV from the arterial, portal venous and washout phases, and get a good idea of motion. In my experience, you can see the tumor well enough in at least 2 of those phases. IOW, you can see it 60% of the time 100% of the time.

 

[evilbooyaa]

For those that use 4D-CT and no fiducials, a couple of questions:

1. Do you take into consideration timing of IV contrast so tumor is scanned during arterial phase? If so, how?
2. Do you contour on all phases or just 0% and 50%/60%?

Thanks

MR Fusion mandatory for all liver SBRT. I think treating a HCC on IV contrast alone is like treating a brain met on a CT head with IV contrast alone.

 

[Ray D. Ayshun]

MR Fusion mandatory for all liver SBRT. I think treating a HCC on IV contrast alone is like treating a brain met on a CT head with IV contrast alone.

Anectdotally, I've heard from radiologist friends that there's no big difference between mr and ct with respect to known lesions, as long as you protocol things correctly. Screening is a different story of course. I'm happy to see something that contradicts this, but all I could find had to do with screening.

 

[evilbooyaa]

Anectdotally, I've heard from radiologist friends that there's no big difference between mr and ct with respect to known lesions, as long as you protocol things correctly. Screening is a different story of course. I'm happy to see something that contradicts this, but all I could find had to do with screening.

Fair point, if you're doing a dedicated triphasic liver CT protocol then I could see that argument. I guess I don't have faith in Rad Onc therapists doing that at time of CT Sim.

 

[medgator]

Any good constraint table for adrenal sbrt? Do people just extrapolate from liver constraints?

 

[evilbooyaa]

Respect OAR tolerances. I go lower than Timmerman numbers because my focus in oligomet patients is not to hurt them. Baically treat in a risk-adapted approach. Depends on anatomy. I've gone as high as 50/5 to adrenal mets when pancreas or liver are blocking well, and as low as 35/5 if stomach or duodenum very close.

 

[BobbyHeenan]

Respect OAR tolerances. I go lower than Timmerman numbers because my focus in oligomet patients is not to hurt them. Baically treat in a risk-adapted approach. Depends on anatomy. I've gone as high as 50/5 to adrenal mets when pancreas or liver are blocking well, and as low as 35/5 if stomach or duodenum very close.

This has been my approach as well. And I think I remember reading in SABR comet they prioritized dose constraints well above that of target coverage. Someone verify that though.

 

[Ray D. Ayshun]

MR Fusion mandatory for all liver SBRT. I think treating a HCC on IV contrast alone is like treating a brain met on a CT head with IV contrast alone.

Thinking back to the comment about SRS, I totally agree. On the other hand, I wonder how contouring on a hi-res contrasted CT sim would do compared to a fused MRI. Based on everything that's been published in the past, particularly cervix and prostate stuff, the GTV will be bigger. In turn, based on some PTV expansion studies in SRS, we might expect more Radionecrosis if CT alone is used?

 

[evilbooyaa]

This has been my approach as well. And I think I remember reading in SABR comet they prioritized dose constraints well above that of target coverage. Someone verify that though.

This is true, although some question their tolerances as the rate of G5 toxicity was higher than what I would consider acceptable.

 

[evilbooyaa]

Thinking back to the comment about SRS, I totally agree. On the other hand, I wonder how contouring on a hi-res contrasted CT sim would do compared to a fused MRI. Based on everything that's been published in the past, particularly cervix and prostate stuff, the GTV will be bigger. In turn, based on some PTV expansion studies in SRS, we might expect more Radionecrosis if CT alone is used?

In the rare situations where I've had to draw on CT w/ contrast alone (absolute contraindication to MRI) I would do 2mm PTV instead of 1mm, as well. Additional risks of radionecrosis with that are not trivial. Lead to fractionating a decent amount of those situations (since usually CT visible lesions are larger than MRI visible lesions).

There can be subtle MRI enhancement at periphery of a CT-based lesion. Not scientific, but would make me concerned about doing 1mm PTV.

 

[ramsesthenice]

Just wondering how you contour the tumor on each phase of the 4DCT if you can’t see the actual mass. MRI abdomen is generally only acquired with a breath hold.

I fuse liver to liver on all phases and then punch it out based on tumor location in the contrasted scans. Not perfect, but I use decent PTV margins on top of an ITV and our control has been quite good.

Anectdotally, I've heard from radiologist friends that there's no big difference between mr and ct with respect to known lesions, as long as you protocol things correctly. Screening is a different story of course. I'm happy to see something that contradicts this, but all I could find had to do with screening.

Yes and no. I'd argue this is only partially true. You can get a reasonable look at most lesions on the right CT images but if the tumors have much heterogeneity in terms of enhancement (which most do) good luck contouring with any high degree of confidence. Admittedly, most of the time there is an easy solution: contour generously. This is not brain. You won't get symptomatic necrosis in the liver. I see a fair number of these that can't get an MRI for some reason another and it is definitely doable with good results. But so are 2D point H based T&Os. Doesn't mean I will go out of my way to do them...

 

[RadOncMegatron]

Great thread (a throw back to the old school SDN days). I really like RTOG 1112 with its multiple dose levels based on constraints. I try for 50 / 5, but step down based on OARs.

As for imaging, there is usually a dedicated liver CT and MRI by the time they come to me, for me, the MRIs are so much easier. So now I ask for fiducials and then obtain an MRI. 4DCT (no gating) with ITV construction. I believe PMH does 6 Gy x 6 for HCC with good results if all else fails (I recall a lecture by Dr. Dawson saying HCC is sensitive to XRT so no real need to go that high???). I feel fine treating CP Score A-B7, but below that I get nervous.

 

[Lamount]

In HCC it's nice to know what the rest of the liver looks like. Our hepatologists generally make a biopsy of the normal liver to rule out any liver pathology when they perform biopsies for HCC. I presume the lesion in small and you will not run into any troubles meeting liver constraints, right?

This is fascinating... it makes sense.
Where I trained, you didn’t routinely biopsy LIRADS 4-5 lesions. We just treated assuming that it was HCC

 

[Lamount]

MR Fusion mandatory for all liver SBRT. I think treating a HCC on IV contrast alone is like treating a brain met on a CT head with IV contrast alone.

Treated a few patients where the simulation scan was a carefully timed triphasic contrasted CT with bolus tracking, and images were easier to use than the MRI

I think there are pluses and minuses to both. With MRI, I worry that the internal anatomy may be slightly different between the two scans.

 

[ramsesthenice]

I recall a lecture by Dr. Dawson saying HCC is sensitive to XRT so no real need to go that high???

People go back and forth on radiosensitivity of HCCs. But your approach is a good one. Need to keep in mind that not very many people will die of HCC. They almost all die of the liver disease that caused their HCC in the first place. Palliative doses are not ablative but can do a decent job of providing adequate control. I saw someone last week I palliated about six months ago for a huge (10 cm) symptomatic HCC. AFP was >90K pretreatment. Did 5 x 5 with complete symptom resolution. Tumor is currently around 6 cm and AFP is still high but "down" to 3500.

 

[metview]

For those that use 4DCT, do you time the scan so tumor is imaged during arterial phase?

If you don't use fiducials, then I think you would have to scan during arterial phase or else there would be no way to see the tumor and account for motion?

 

[ramsesthenice]

For those that use 4DCT, do you time the scan so tumor is imaged during arterial phase?

If you don't use fiducials, then I think you would have to scan during arterial phase or else there would be no way to see the tumor and account for motion?

I don’t. I fuse the sequences liver to liver with the arterial phase and copy the tumor contours on each phase. Use a generous PTV (7-10 mm on top of ITV)Works well.

For patients who don’t need gating I treat with MR linac since MR IGRT is an efficient way to align to tumor.

but as I eluded to above, post TACE SBRT is super easy with KV imaging. No benefit of MRI for them.

 

[evilbooyaa]

For those that use 4DCT, do you time the scan so tumor is imaged during arterial phase?

If you don't use fiducials, then I think you would have to scan during arterial phase or else there would be no way to see the tumor and account for motion?

Two different issues - fiducials are for IGRT. Contrast during arterial phase (not unreasonable) is for developing the initial contour. Fiducials don't help you contour the disease, and you can't give IV contrast at time of CBCT. That's the main issue with no fiducials in liver SBRT - can be very difficult to see anything on a non-con CBCT. Obviously very different from a non-con CBCT for NSCLC.

 

[Ray D. Ayshun]

For those that use 4DCT, do you time the scan so tumor is imaged during arterial phase?

If you don't use fiducials, then I think you would have to scan during arterial phase or else there would be no way to see the tumor and account for motion?

TBH, I can't recall where/when/if 4D fit in wrt contrast administration (it may have just been done without), but if you have a protocolled triphasic scan, just combining all three scans when free-breathing should be enough to generate a good ITV. Watching diaphragm motion on fluoro could give you an idea of motion, too, and if you should make the PTV expansion slightly greater sup/inf.

 

[ramsesthenice]

if you should make the PTV expansion slightly greater sup/inf.

Amen. I feel like a lot of people have it their heads that PTVs should be isotropic expansions based on setup and motion uncertainty. Using an isotropic expansion assumes uncertainty is even distributed in all directions but if your 4D tells you that motion is not evenly distributed in 3 dimensions that is not a great assumption. Some of my colleagues argue that when expanding from an ITV the additional uncertainty (beyond what is accounted for on 4D) should be relatively evenly distributed but I am not sure that is an entirely fair assumption. We are really splitting hairs here and in all reality this is mostly an academic debate.

 

[evilbooyaa]

Amen. I feel like a lot of people have it their heads that PTVs should be isotropic expansions based on setup and motion uncertainty. Using an isotropic expansion assumes uncertainty is even distributed in all directions but if your 4D tells you that motion is not evenly distributed in 3 dimensions that is not a great assumption. Some of my colleagues argue that when expanding from an ITV the additional uncertainty (beyond what is accounted for on 4D) should be relatively evenly distributed but I am not sure that is an entirely fair assumption. We are really splitting hairs here and in all reality this is mostly an academic debate.

I suppose I'm in the camp of arguing that if you're doing a proper ITV on a free-breathing 4DCT scan (without repsiratory gating), if you are confident in your ITV then PTV should be symmetric.

Not the case with say end expiratory breath hold scans, or free-breathing non-4D scans, where my PTV margins change drastically. Similarly if I was doing repsiratory gating, I'd consider expanding PTV a little bit more in the direction that the tumor seems to be going as if I wasn't doing gating.

 

[RadOncMegatron]

Amen. I feel like a lot of people have it their heads that PTVs should be isotropic expansions based on setup and motion uncertainty. Using an isotropic expansion assumes uncertainty is even distributed in all directions but if your 4D tells you that motion is not evenly distributed in 3 dimensions that is not a great assumption. Some of my colleagues argue that when expanding from an ITV the additional uncertainty (beyond what is accounted for on 4D) should be relatively evenly distributed but I am not sure that is an entirely fair assumption. We are really splitting hairs here and in all reality this is mostly an academic debate.

I'm more in this camp. I take a look at the how tumor is moving (more pertinent for lung I suppose) and the lateral motion is usually not as bad as the sup / inf. For VMAT based plans, there is more spread lateral along the axis of the plane. The dose fall off is much sharper sup / inf thus I sometimes enlarge my PTV in that direction due to the uncertainty of it all.

TBH with all that said I probably >90% of the time just do a concentric PTV.