Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

Summary:

3 alternate approaches to head and neck IMRT for primary tumor located above the level of larynx: highly debated issue

Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

Ayan Basu 24 Jan 2011 07:41

Excellent article discussing the pros & cons of 3 alternate head and neck IMRT techniques for supra-laryngeal primary tumors:

1.Whole neck IMRT
2.Upper head and neck IMRT with split beam matched low anterior neck fields
3.Upper head and neck IMRT with gradient matched low anterior neck fields

Link: http://download.journals.elsevierhealth.com/pdfs/journals/1879-8500/PIIS1879850010000056.pdf

Members' comments : would love to know which technique is preferred at different centers-i guess most centers have used all of the above and have decided to prefer one over the other - any particular reasons from your experience ?

I feel the final sentence sums up the practice @ Univ Florida : they use whole neck IMRT for patients with high risk of disease in the posterior portion of lower neck and matched ( split-beam or gradient matched ) low anterior neck fields with upper head and neck IMRT for patients with low risk of disease in the posterior portion of lower neck, since a standard prescription of 2Gy @ 3cm depth as they have followed would under-dose the posterior region of the lower neck.

Last edited on 24 Jan 2011 10:02 by Ayan Basu Show more

Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

AAM 24 Jan 2011 11:43

can we have the reference, I can't access the PDF as it is protected.

We don't use a split beam. You can force a near similar plan by making the midline structures from larynx down very high priority with a very low dose.

I can't see any advantage in a split field, only disadvantages.

Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

Ayan Basu 24 Jan 2011 12:59

Reference :

Practical Radiation Oncology (2011) 1, 27–32

Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

Suruchi Singh 24 Jan 2011 11:35

Hi Ayan,
Frankly, i hav seen, done, n practiced only "whole neck IMRT"; I am personally very doubtful abt the matching, when we combine two IMRT or one IMRT with another conventional plan!! I understand that we do rely on same systems for planning but wen it comes to combining plans I hav my own reservations for scatter doses, MLC leakages, low dose regions (as we have been recently discussing) n hence I avoid the same both in 3D as well as IMRT.
As far as laryngeal blocks r considered i can recollect seeing at least 2 kids treated for lymphoma developing recurrences adjacent to blocks, i hav not searched literature supporting the same as yet… lets see wat others hav to say!!!

Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

Santam Chakraborty 25 Jan 2011 03:28

Hi all I have a fundamental question to pose here.
Look at the image below. Most of you will recoginze it from the RTOG N0 contouring atlas. I have added the opposite side contours for level III and the contour for the larynx as per the publication. Even assuming early nodal disease N1 with say a less than 1 cm node for a well lateralized T1 tonsil we will contour at least the ipsilateral level III in the nodal CTV (correct me if I am wrong here). The dotted line is the PTV - handdrawn of course on krita.

I am depicting the midline shield here also as would be essential to spare the larynx (with a margin for PRV around the larynx). Even assuming there is no prv for the larynx as you can see there is difficult to spare the larynx while treating the level III with a direct anterior field.

Now we have two options available:

1. Accept an underdose of the CTV or an overdose of the larynx - I presume most of us will favour the latter.
2. Contour the CTV away from the recess between the Sternocleidomastoid and the larynx - thereby generating a seperation between the CTV and the larynx so that the shield can be placed

As Andrew says both situations can be planned on IMRT. If we give a sufficient margin between the larynx and CTV as in the second case we can spare the larynx with IMRT also giving a higher constraint to the larynx.
Further from my 3DCRT days I know treating the neck with a single anterior field always gives a suboptimal dose distribution with coverage of the PTV seldom more than 90% prescribed dose even after a 3 cm prescription and a bad overdose on the skin surface. If you give the same loose constraints on IMRT we can spare the larynx even further.

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Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

Suruchi Singh 25 Jan 2011 05:21

The pics have made it absolutely clear, Santam. I feel instead of modifying the CTV's, we can set priorities separately for cartilage n soft tissues (major part of strictures n fibrosis will be contributed by s.t.).

Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

Santam Chakraborty 25 Jan 2011 07:00

Good point Suruchi,
However the issue with dysphagia at least is not so simple as sparing the larynx only. Levendag's publication in this regard is instructive as is the basic anatomy of pharyngeal musculature we study in Grays. If we have to meaningfully spare dysphagia by reducing dose to the dysphagia aspiration related structures then we will have to give constraints to entire circular muscle apparatus made of the three constrictors which is very difficult to do for most head and neck cases.
Furthermore I am not sure of how much sparing we can achieve actually with contouring the cartilage and mucosa seperately .. simply the physical seperation between them is not so much that a siginificant dose gradient can be generated.

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Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

Ayan Basu 26 Jan 2011 10:45

Great pictures Santam, illustrates a very valid reservation against midline block.
Andrew, Suruchi , Santam all agree that whole neck IMRT is better than Low anterior neck with midline block in the above scenario , for aforementioned reasons.I am yet to hear a counterpoint. Literature , albeit somewhat older , is rife with Low ant neck fields and matching techniques , though-i believe for the reason stated below—
The other important issue in whole neck IMRT is shoulders coming into couple of gantry angles which are optimal ( 'Beam angle optimisation' will often ask you to treat through shoulders unless you manually adjust) for the distributions in the high risk volumes above which we have to unfortunately treat with the same optimized plan. However , with 'Fixed Jaw Optimisation' and superior optimisation algoritms for IMRT and also 'Skip Angles' in volumetric arc therapy , it is not so much a reason for concern —OR IS IT ?

Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

Santam Chakraborty 26 Jan 2011 19:57

Going through the article again I am really struck by how little difference there is in the doses to the larynx. Reducing the laryngeal dose from 30 Gy to 26 Gy does it make a big difference. The key issue with the article that I felt was that they were comparing modalities w.r.t OAR without concerning themselves about the target. The CTV in the split beam plans was different and truncated as compared to IMRT. The authors did not give the constraints they used for IMRT. I am sure the doses with IMRT would have been much lesser with the truncated CTV and hard constraints on the larynx. After all if you are blocking a structure your penalty or priority for the structure is highest but with IMRT your penalty for the same structure is like 10 times less than the target - they had a penalty of 0.1 for larynx and 1.2 for target .. go figure . We are not comparing oranges with oranges and apples with apples here

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Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

radtuxabhishek 29 Jan 2011 06:55

There are a number of assumptions in the present study; I'd like to highlight some of the shortcomings of the discussed paper.

1) The end point is related to dysphagia; it should have been perhaps voice quality.

2) All patients of orophayrnx with only ipsilateral nodes under study.

3) The debate would have been more instructive for nasopharynx/unknown primary.

4) What would have been the impact of the planning had higher coverage been warranted; as per the new ICRU "guidelines"; those interested in homogeneity should "contemplate"! I am not interested in homogeneity of the dose but I would prefer to look for "any island" of "cold spot", if any.

5) Shielding the larynx with a midline block in split field IMRT is theoretically good enough; however, we often forget the contribution from scatter dose to the spinal cord.

6) Although there has no literature documenting the match line failures in Head and Neck (squamous cell carcinomas), it can become a issue for "excessive dose" though as Santam pointed it out.

The big question. In case of elective treatment of the neck (eg. in oropharyngeal primaries) by using IMRT, should it be possible to reduce the dose to the neck to 40 Gy? There is a trail on going by Ghent University (I think) which would answer that question effectively looking for patterns of failure. The idea is to be able to reduce the dose to DARS (AND) larynx.

The shoulders can easily be excluded from the field in extended field; one way out is to use zero transmission block which can be removed AFTER the optimization process. Hence only the MLC's would stay there. Or use a collimated field!

In case a split field is really required, I would go in the same if I am treating oral/oropharyngeal primaries. For nasopharynx/unknown primaries, it would be worthwhile to use extended field with a higher constraint to larynx (around 35 Gy). For any retrospective review, voice quality is paramount followed by assessment of dysphagia (in terms of say PEG/ ryle's tube dependence).

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Reality is merely a persistent illusion

Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

Santam Chakraborty 30 Jan 2011 21:36

Actually there is an article now comparing the clinical outcome of patients treated with a single low neck field versus whole neck IMRT.
Turaka A, Li T, Nicolaou N, Lango MN, Burtness B, Horwitz EM, et al. Use of a conventional low neck field (LNF) and intensity-modulated radiotherapy (IMRT): no clinical detriment of IMRT to an anterior LNF during the treatment of head-and neck-cancer. Int. J. Radiat. Oncol. Biol. Phys. 2011;79(1):65-70. (Find PDF below)

A retrospective study with several pointers as to why a LNF need not be used.
A short summary of the results:

1. 153 patients treated
2. LNF fields used in patients without nodal disease at the level of larynx
3. N2 or more disease in 24% in LNF vs 38% on IMRT
4. 51% in IMRT stage IV vs 38% in LNF
5. T3/4 tumor 47% in IMRT vs 31% in LNF
6. LNF used for treating early cases primarily
7. Dose to low neck was 46 -50 Gy at 3 cm depth treated with a LINAC
8. IMRT elective node received 56 Gy / 54 Gy in post op setting
9. Larynx dose limited to < 40 Gy with IMRT
10. Layngeal toxicity during treatment was seen in 1 patient (n = 37) vs 5 patients with IMRT (n =54)
11. 32% and 50% had ND after RT in IMRT and LNF arm respectively when nodes > 3 cm were identified
12. Pharynx/Esophagitis 25/37 in LNF and 38 / 54 in IMRT (NS)
13. Late pharyngeal toxicity 4/54 in IMRT and 1/37 in LNF (all gr II , P NS)
14. No significant differences in locoregional control or peg tube use or toxicity in either techniques after accounting for stage etc.

What is important in the study is that it illustrates the point that IMRT with appropriate constraints will lead to near similar dosimetric and similar clinical outcomes as with laryngeal blocking and a low neck field. Blocking 2 cm of the larynx can give a slight reduction in hoarseness and laryngeal edema but is unlikely to influence pharyngeal toxicity significantly as it depends on the interplay of the dysphagia aspiration related muscles. So reducing laryngeal edema alone may not be suffecient to give an aspiration free larynx. Another issue is that with IMRT and appropiate constraints I can actaually reduce dose along the entire esophagus as well the lower third of pharyngeal constrictors .. try doing that with a single low neck field which cooks the esophagus very nicely.

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Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

dr Arun S 31 Jan 2011 16:58

I agree with what Abhishek says about patient selection…
For Patients with Oral Cavity & Oropharyngeal primaries and node confined to level 1 or 2, I would not mind a little underdosing of the posterior part of neck.
Where as for Nasopharynx primary, I would be concerned.

The way we practice here (RCC, Trivandrum), in patients with nodes only high up in the neck, we generally use a 2cm midline shield for the entire length of LAN {that will underdose medial part of nodal area - medial part of carotids in level 3 region, but lower down more generous portions of level IV gets shielded…} We even prescribe a lower dose of 45 Gy / 20# at 3cm depth….. and isolated recurrence in the LAN field was not noted ( we do have lost to follow ups !!!). So how important is the underdosing…

Due importance should also be given to the shape of the neck. A very rounded thick neck - you are likely to significantly underdose the posterior neck !! IMRT would be better

If a separate LAN field, would make it possible to generate a better IMRT plan, then…..

Finally from Patient's perspective, dysphagia (RT/PEG dependence) is more important than voice "Quality".

Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

Santam Chakraborty 01 Feb 2011 00:46

Good points there arun. one of the compulsions of using imrt in the SIB format is the necessity to give 54 Gy or thereabouts to the lower neck in order to maintain an acceptable dose per fraction. We really have very little data on what dose is required for microspcopic disease eradication. The practice you have followed at RCC Trivandrum had been followed in large number of North American Centres courtsey Fletcher (though Gunderson is against it) with quite good results. And that is the basis of my point - when we are treating with IMRT that means we dont really need to delineate the CTV as the atlas says. Trimming the CTV by a cm from the larynx unless there are grossly involved nodes and constraining the IMRT optimisation process for larynx specifically should do wonders to the dose.

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Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

radtuxabhishek 31 Jan 2011 17:39

I'd just like to clarify about the voice quality versus dysphagia.

There are a number of issues competing for dysphagia; as pointed out by Santam, related to the fibrosis of the pharyngeal wall (DARS); in IMRT plans I doubt whether 30-35Gy would actually contribute to the dysphagia. The end result in these cases (over a long period of time in follow up) has to be the "laryngeal edema" and voice quality/timbre. Although, this may well be subjective since I am not aware of any "definitive scores" about voice quality though.

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Reality is merely a persistent illusion

Re: Whole neck IMRT Vs Low Ant Neck field with Split Beam Vs Gradient Matching

Santam Chakraborty 01 Feb 2011 00:50

Actually Abhishek we really dont know what dose levels are safe… very little data is actually reported on this except from a couple of groups. One interesting point is that fibrosis at the level of the muscle often doesnot manifest until 5 -6 years so later on patients may have more swallowing issues than they do say an year or two after RT. This is something I have come across in the clinics here that the swallowing does get somewhat restricted after 4 -5 years .. which actually not difficult to forsee if you have seen the fibrosis in the skin that happens in the patients after 5 years (its really not evident or bothersome to the patient before that).
What is important is that we should realise that we are in the long term business .. our patients live long and come back with complications and any complication we can reduce or prevent is better. Concerning ourselves with response rates should not be our outlook unlike what is seen in the MO world. Infact much of the awareness about the late term side effects in cancer therapy is bought about by the pioneering work of Radiation oncologists.. medical oncologists are just joining the game.

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