Role of CTV expansion in H&N and Lung primary

[evilbooyaa]

Anyone routinely skipping CTV expansions off the GTV (that are taken to the gross disease dose) in the following situations:

1) H&N definitive RT/ChemoRT, omitting a 70Gy 'CTV' expansion of 3-5mm for the primary, in say a Oropharynx patient
2) Same as #1, but for a positive lymph node
3) Definitive chemoRT for lung cancer (NSCLC, LS-SCLC), in regards to the primary
4) Same as #3, but for positive lymph nodes

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[Palex80]

That is a very good question and the answer is quite complicated.
The first thing that comes to mind is: If you skip a GTV-CTV-expansion, what is your GTV-PTV-margin?

Other than that, I find that skipping a CTV-expansion is a lot easier for lymph nodes than it is for the primary tumor.
Here is an older article discussing ECE around nodes and implications for radiotherapy planning:

Quantitative Analysis of Extracapsular Extension of Metastatic Lymph Nodes and its Significance in Radiotherapy Planning in Head and Neck Squamous Cell Carcinoma

We performed a histopathologic analysis to assess the extent of the extracapsular extension (ECE) beyond the capsule of metastatic lymph nodes (LN) in…

www.sciencedirect.com

And the last question that comes into mind are diagnostics. If you are skipping the expansion, what methods are you using to make sure you don't have any geographic miss? Do you skip the expansion only if you have an MRI performed the same day you did the planning CT or do you contour based on a PET-CT for HNSCC? Would you be less willing to skip the expansion if this was a base of tongue primary and your MRI is 2 weeks old?

 

[gmsquid]

I’m only answering for hn. I routinely do 3-5 mm. Largely because we know there is some gross disease that can’t be seen on imaging from path series at the primary site and neck. Another article similar to Palex: Determining optimal clinical target volume margins in head-and-neck cancer based on microscopic extracapsular extension of metastatic neck nodes - PubMed

Also, recent gregoire guidelines recommend your ctv1 to be at least 5 mm on primary based on these studies:

Delineation of the primary tumour Clinical Target Volumes (CTV-P) in laryngeal, hypopharyngeal, oropharyngeal and oral cavity squamous cell carcinoma: AIRO, CACA, DAHANCA, EORTC, GEORCC, GORTEC, HKNPCSG, HNCIG, IAG-KHT, LPRHHT, NCIC CTG, NCRI, NRG On

Implementation of these guidelines in the daily practice of radiation oncology should contribute to reduce treatment variations from clinicians to clinicians, facilitate the conduct of multi-institutional clinical trials, and contribute to improved care of patients with head and neck carcinoma.

pubmed.ncbi.nlm.nih.gov

 

[isrradonc]

Not yet for lung, I typically add a 7mm margin to GTVp and 5mm non-uniform margin to GTVn (cover the station) to create CTVs. I also use the 4D to confirm all the gross disease is encompassed in the CTV even with movement.

 

[RadOncDoc21]

I still do it still for H&N and other lungs but my volumes have come down significantly for all sites mainly because of better imaging and the use of CBCT (yes daily).

 

[medgator]

I still do it still for H&N and other lungs but my volumes have come down significantly for all sites mainly because of better imaging and the use of CBCT (yes daily).

Don't see any advantage imo over daily Kv outside of longer table time. I continue to do weekly. Bony anatomy still pretty good for things overall and the weekly helps me catch if/when a replan might be needed

 

[RadOncDoc21]

Don't see any advantage imo over daily Kv outside of longer table time. I continue to do weekly. Bony anatomy still pretty good for things overall and the weekly helps me catch if/when a replan might be needed

I just like the advantages of seeing subtle changes but it’s mostly for the therapists to use. They seem to be more comfortable with it and I have been able to pick up changes that needed to be replanned but likely something that could have been picked up the same week. This is another reason why my volumes have significantly changed.

 

[StIGMA]

Cannot answer 'none' in the poll.

 

[Ray D. Ayshun]

For HN I treat two volumes, gross and elective, no intermediate. I make my bigger CTV first (elective nodal plus 1 cm or so around the primary) and add 3 mm for PTV, then I just expand the GTVs by 1 cm to my PTV hi and crop anything that extends outside the lower dose PTV. Works out to a 6-7 mm CTV expansion more or less, which my be overdoing it for nodes per se, but I feel like it's a middle ground wrt the intermediate dose commonly employed. Anatomic barriers are taken into account.

For lung, I go back to the surgical studies where 6-8 mm microscopic extension was found where the primary was resected, depending on histology, which I don't take into account. I just expand as much as I safely can based on disease burden/underlying lung function. For nodes, 3 mm. I'm also a fan of connecting my primary to the hilum even when negative. As in, I don't like a PTV in lung that has an untreated area between the primary and mediastinal/hilar disease, except in cases of upper lobe tumors, where skipping the hilum makes more sense, or when the separation is great, I like to consider the path the cancer took and treat if not too unreasonable.

In short for me, i technically always do a CTV.

 

[evilbooyaa]

Cannot answer 'none' in the poll.

Good catch, a 5th option has been added!

I am aware of what guidelines state and what protocols require (which is where this thought originated from in the other thread) that none of these scenarios should be omitting CTV margin. I am simply asking for personal practice.

I had a H&N/Lung attending that swore by no CTV margin for all gross disease doses but would at times do a lower dose CTV (say 50-54Gy for definitive lung, or 56 or 63Gy for HPV+ and HPV- H&N, respectively) to what most would contour as 'CTV'.

That being said, I have NEVER done CTV expansions on H&N nodes given that they're surrounded by a 50-60ish Grey nodal volume anyways. GTV --> PTV - usually 5mm in H&N but 3mm at times if field is small. I am also a daily CBCTer and I've seen KVs look good but the CBCT that follows requires additional shifts. All of my IMRT gets daily CBCT.

 

[evilbooyaa]

Not yet for lung, I typically add a 7mm margin to GTVp and 5mm non-uniform margin to GTVn (cover the station) to create CTVs. I also use the 4D to confirm all the gross disease is encompassed in the CTV even with movement.

So you don't create an iGTV using 4D for definitive lung cases? You draw GTV on your planning scan (free breathing or average) expand, and then verify on 4D? See, I suppose here's my issue with that. You're not really covering microscopic extent of disease uniformly with something like that. I create a iGTV (I call it an ITV, but YMMV) on MIP or all phases (if abutting chest wall, mediastinum, hilum, etc.) then expand. In residency one attending did CTV expansions, another didn't, but it was always an expansion of the iGTV. I now do 0-5mm CTV along iGTV and an additional 5mm of PTV. Again, daily CBCT.

 

[kimplera]

only qualified to comment on HN -
We have used a GTV-PTV expansion of primary and nodes for quite some time and recently published a couple articles on it:
Clinical outcomes for larynx patients with cancer treated with refinement of high-dose radiation treatment volumes.
Reducing radiotherapy target volume expansion for patients with HPV-associated oropharyngeal cancer.
Very much dependent on good imaging. My typical approach is GTV=CTV70 and then contour high risk nodal CTVs which go to 60-63 and low risk nodal regions which go to 54-56. The nodal CTV extends approximately 5mm around any gross nodes. nearly all PTVs are 3mm except for paranasal sinus/skull base tumors where i may use 2mm and have discussion with therapists about alignment. Only do 2mm if i have the 6degree freedom couch - Most of our HNC are treated on tomo but make exception for those with sparing of optic nerves/brainstem/chiasm. Lots of subtly here and we are trying to figure out if can be safely done at our centers without the same physics/therapists that we have (i know, i know - ivory tower... trying to get funding for a D&I grant)

 

[Phantom1]

For head and neck I use a GTV-CTV expansion of 3-5mm for primary. For LN if it is well circumscribed then GTV=CTV, but if its a conglomerate or any concern for ECE then I use 3mm GTV-CTV expansion. This follows general principles of microscopic or mucosal disease which we cannot see on CT. Overall I feel like we are shrinking volumes a little too much for many disease sites. The comparison of treating the entire head and neck as one volume with conventional versus now carving off IMRT/VMAT volumes to have 3mm off gross disease is pretty striking. It is walking a fine line between trying to reduce side effects versus compromising locoregional control...

Analogy from another disease site would be prostate and reducing posterior margin to 2-3mm.. sure its great and reduces rectal toxicity and patients breeze through treatment and no GI referals... but are there more locoregional failures down the road??

 

[RadOncMegatron]

Good catch, a 5th option has been added!

I am aware of what guidelines state and what protocols require (which is where this thought originated from in the other thread) that none of these scenarios should be omitting CTV margin. I am simply asking for personal practice.

I had a H&N/Lung attending that swore by no CTV margin for all gross disease doses but would at times do a lower dose CTV (say 50-54Gy for definitive lung, or 56 or 63Gy for HPV+ and HPV- H&N, respectively) to what most would contour as 'CTV'.

That being said, I have NEVER done CTV expansions on H&N nodes given that they're surrounded by a 50-60ish Grey nodal volume anyways. GTV --> PTV - usually 5mm in H&N but 3mm at times if field is small. I am also a daily CBCTer and I've seen KVs look good but the CBCT that follows requires additional shifts. All of my IMRT gets daily CBCT.

Pretty much same way here. It's all voodoo, but I still do 5 mm GTV --> CTV for lung since the doses suck (ie just 60 Gy) and there is no elective volume. I don't want to take any chances. Honestly, I know the 6 mm SCCa and 8 mm adenoca paper , but its just a retrospective paper and dose spillage after a 5mm CTV expansion in the D95% VMAT era is likely sufficient. As a side note, I always do a 4DCT with an ITV and I do let my lung plans run a little hotter ie for a 60 Gy plan it looks like a 62 Gy plan due to trying to push that dose through terrible thin lung tissue, so I think the 6 mm and 8 mm is getting enough.

For H&N I drop the CTV due to the surrounding low dose 56 Gy in the elective volume. For p16+ (unless locally adv beast) I don't bat an eye, but for ECE or just a p16- making me uncomfortable, I may add in a cheater 63 Gy as a precaution. Like I said voodoo. For the typical OPC p16+, my gut feeling is that, going from 56 --> 63 or 5412 --> 5940 prb makes little difference to microscopic tumor (which may or may not be there and likely not there ie its 15% chance right?), but may make a difference to normal structures (which have a 100% chance to be there).

It is nice to see that many of us are thinking the same way. Great and helpful discussion!

 

[drewdog1973]

Good discussion.

MSKCC appears to have gotten rid of the CTV expansion for HNC, while MDACC maintains it (5-10mm). If you have good imaging (CT, PET, MRI and IGRT), not unreasonable, but it is certainly outside of protocols and guidelines. Someone can else can do the math, but adding 5-10mm, editing out of bone/non-contiguous mucosa, then adding another 3-5mm for PTV is a ton more volume receiving 70 Gy. If the rationale for CTV is microscopic diseasease and the GTV is getting 70 GY, then with dose fall off, 5mm outside of of that is getting microscopic dose, I presume.

I have not dropped CTV, but I can see that being the future.

 

[Lamount]

I have always used a 3-5 mm CTV margin on H&N primary and 3 mm margin on LNs (+3 mm PTV)... though this is not my current area of expertise.

In the chest...
I use a 5 mm CTV on parenchymal tumors when treating with CRT (+5 mm PTV)
I use a 0-5 mm CTV margin on LNs but do not extend this beyond anatomical compartments. I am reluctant to be skimpy with CTV margin WITHIN the mediastinum as I think there is a high liklihood of microscopic disease adjacent to involved LNs (i.e. the same reason I would still recommend PORT for N2 patients).

I don't use a CTV with any SBRT or other ablative/hypofractionated treatments (5 mm PTV --rarely 3 mm next to the pericardium as per Hasbeek). It's not that I think the biology is different, but the data are... and the halo of high-BED dose may be accounting for microscopic disease.

 

[FrostyHammer]

head/neck
* primary: I make a GTVp -> expand by 1.0 cm for CTV70 and then crop judiciously -> expand 0.5 cm for PTV70 -> expand 0.5 cm from there to make a CTV at intermediate dose level -> expand 0.5 cm to make int dose level PTV
* involved nodes: I make a GTVn -> expand 0.5 cm to PTV and if needed crop from skin for planner
* elective nodes: I make a relatively more generous CTV -> expand 0.3 cm to PTV

lung
* primary: I make an iGTVp -> expand by 0.5 cm for CTV and crop judiciously -> 0.5 cm to PTV
* involved nodes: I make a GTVn -> expand by 0.5 cm for CTV but liberally cut based on anatomy and such factors, and slightly expand in other areas where there is high risk of subclinical dz not found on PET (this is pseudo-RNI but is almost always in the same station & just abutting the involved node) -> 0.5 cm to PTV

Daily CBCT for both

 

[isrradonc]

So you don't create an iGTV using 4D for definitive lung cases? You draw GTV on your planning scan (free breathing or average) expand, and then verify on 4D? See, I suppose here's my issue with that. You're not really covering microscopic extent of disease uniformly with something like that. I create a iGTV (I call it an ITV, but YMMV) on MIP or all phases (if abutting chest wall, mediastinum, hilum, etc.) then expand. In residency one attending did CTV expansions, another didn't, but it was always an expansion of the iGTV. I now do 0-5mm CTV along iGTV and an additional 5mm of PTV. Again, daily CBCT.

I agree. I wasn't clear. When I say that I verify on 4D, I make sure to have a margin... I think the iGTV method may be easier as you say.

 

[medostrich]

there are papers on this issue, for example:

Cureus. 2016 Jan; 8(1): e466.
Published online 2016 Jan 23. doi: 10.7759/cureus.466
PMCID: PMC4764420
PMID: 26929893

Is a Clinical Target Volume (CTV) Necessary in the Treatment of Lung Cancer in the Modern Era Combining 4-D Imaging and Image-guided Radiotherapy (IGRT)?​