IMRT/Lung

[deleted4401]

You guys do it for definitive treatment? For some patients? For all patients?
If you don't have motion study/4D-CT/gating, do you think fusing free-breathing/inspiration/expiration scans to generate ITV compensates? What sort of PTV with daily imaging? Dose?

Wondering why MDACC's retrospective data showed so much of an improvement with bigger volumes in the IMRT group...

S

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[Palex80]

We don't have 4D-CT/RT.

I only do IMRT in lung when I am treating the mediastinum or centrally located lesions. I am not comfortable with IMRT for peripheral lesions.
In some cases, where I had to treat both, I did IMRT for the mediastinum/hilus followed by SBRT (without IMRT) for the peripheral lesion and worked out a cumulative DVH.

In my humble opinion and experience with IMRT for lung, IMRT is especially beneficial for patients with N3 disease. You can spare some high dose areas in the contralateral lung, which is quite good, since N3 patients usually have lots of N2 stations involved, meaning that the ipsilateral lung takes quite a beating.

 

[alphacentauri]

I use IMRT for most of my locally advanced lung, though if I can get a good plan with 3D conformal I go that way. I always get a 4D CT for planning for the ITV, then add ~7mm CTV (variable somewhat depending on histology, overall volume involved, etc), and generally a 5 mm PTV because we have daily image guidance with CBCT. If I have any concerns with how the pt will set up I use a bigger PTV. I don't currently have gating, and I don't use abdominal compression for conventionally fractionated lung treatments, but I've been considering it since we don't have gating at my center. I've been lucky so far in that most of my lung patients seem to have upper lobe and mediastinal disease, so the respiratory motion is not huge. I do think it's a genuine concern to just use a large ITV when you're talking about >>1cm motion, so I'm currently more likely to think 3D for those patients. But, I've really found IMRT to be a huge help for N3 and bulky N2 patients in keeping the lung doses reasonable. Dose-wise, I try for 66 Gy but will use 60 if the V20 exceeds ~35% on the optimized plan going to 66 Gy.

 

[Palex80]

Do you all feel ok using IMRT without gating, even with 4D-CT?

 

[RadRadRad]

If you are worried about interplay effect, one option if using step and shoot IMRT is to intentionally avoid/limit small beam apertures. There may be a way to control this with sliding window as well.

 

[seper]

For stage III lung Ca treated with chemo and IMRT, what are the current evidence based constraints for lung V5 and V10?