V20 in collapsed lobe?

[thaddeus]

Hello sage SDNers, does anyone have a good rubric for coming up with a V20 dose constraint in a lung cancer patient with a collapsed lobe due to tumor obstruction? I'm planning a patient with a RUL collapse currently; the usual V20 < 30% constraint is easily met, but obviously there is a lot of RUL lung parenchyma getting high dose that is not contoured as lung. I think a more conservative constraint would be appropriate, but not sure how conservative it needs to be. Thoughts?

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[Burt Radnolds]

Hello sage SDNers, does anyone have a good rubric for coming up with a V20 dose constraint in a lung cancer patient with a collapsed lobe due to tumor obstruction? I'm planning a patient with a RUL collapse currently; the usual V20 < 30% constraint is easily met, but obviously there is a lot of RUL lung parenchyma getting high dose that is not contoured as lung. I think a more conservative constraint would be appropriate, but not sure how conservative it needs to be. Thoughts?

If you are meeting V20<30% already you are likely fine, as that is already slightly conservative. I typically think of 35-37% as the upper limits. Additionally in your favor is that the upper lobe is less important than the middle/lower lobes.

I think you are wise to be mindful of the idea of dose to the unaerated lobe, but I am not familiar with a mathematical way to account for this other than applying common sense. If you get overly conservative you may just end up driving dose centrally to the heart/esophagus which could be bad.

 

[thaddeus]

thanks radmonckey! will sleep better with your reassurance.

 

[seper]

It's probably too simplistic, but I personally think of atelectatic lung as damaged beyond hope already.