Just Wondering

[Elaine]

I am working on an article, well, mostly today I was thinking about it, which is a kind of work.

Anyway, I read that up to 95 per cent of cancer begin in the lining of the bronchial tubes. Earlier you told me that CT scans aren't reliable as to masses in the respiratory tree.

So,,,,,, my question is this: Mighten there be a better screening for LC than a CT? Maybe one of those newer bronchosopic (is that a word?) procedures such as virtual bronchosopy or one of the ones that put some kind of substance in the tree that highlights dysplasia?

Or is it that most masses begin further down in the tree and so they more quickly spread to the lung?

What would be the best CT slice to best view the airways? Would it or should it be with contrast?

Thanks

elaine

[teresag]

Well, it depends. (I know, bad answer.)

One of the lovely effects of "light" cigarettes is that smokers inhale more deeply, drawing particles deep into their lungs. So tumors, in the past few decades, are showing up in the periphery, not just the central parts of the lungs like they did in the good ole days. The predominant cell type, squamous, is declining in prevalence as adenocarcinoma becomes more common. Squamous cell cancers tend to arise in the central lungs and adeno, you guessed it, in the periphery.

Autofluorescence bronchoscopy is nifty, but costly. It works because tumors fluoresce at different wavelengths than regular tissue. So under certain lighting, a superficial cancer becomes visible to the eye. Neat idea, but who should have it done? Everyone? Every current smoker? Every current and former smoker? Everyone whose home has a certain radon level? You see the problem.

A bronchoscopy requires light sedation and entails time off work, too. Autofluorescence bronchoscopy is also done with injection of a drug that makes the patient quite sensitive to light; this can be a huge drawback if the photosensitivity lasts for long, which depends upon the drug that is used. And, finally, you can't get a bronchoscope into the peripheral parts of the lung.

So it's a tough problem, to understate it.

[kimblanchard]

I think I perhaps didn't clarify what I meant in my previous response. It is true that the vast majority of lung cancers start in the bronchial tubes. To better illustrate this, think of your lungs as a tree. The main trunk is the trachea which branches off many many times into smaller and smaller limbs. The leaves would be the air sacs or alveoli. Lung cancer starts on the inside of these branches and as it grows begins to form a mass which you can see from the outside.

CT scans are limited in that they can only see things that have turned into a mass. They can't see the inside of hollow structures that well but once their have been a few branching of the bronchial system, the hollow tubes rapidly become microscopic anyways. Virtual bronchoscopy has few advantages over a high resolution CT scan except for the ability to see the interior architecture of the larger bronchi. It would be theoretically useful for surgical planning for example. Other than being less invasive than regular bronchoscopy, I do not know of any other advantages besides some very pretty pictures.

Fluorescent bronchoscopy has a number of limitations. First is that as a screening tool, the risk of complications would be too high. Also, from a cost standpoint, it would literally bankrupt our health care system to do this in every person at risk for lung cancer. We would also need to train about 10 times as many pulmonologists as we presently have to be able to do this. Finally, you are still looking at only a very small portion of the lung because th scope can't fit into the vast majority of the bronchi.

Current high resolution CT scans take a slice every millimeter and do so in a single breathhold. It would be most feasible to do them without contrast (which adds very little to a screening test). Of course, the problem with that kind of resolution is that nearly ever CT scan is going to be abnormal. Most of the algorithms call for follow-up scans at a certain interval to see if the spots grow further. Let me just pose this question: how many people on this board would be willing to "sit" on a nodule that showed up on a scan? If many people are not, then we get into the realm of doing lots of extra testing or even invasive procedures which will in the majority of cases be unnecessary.

I think CT scans are/will be the best screening tool for lung cancer. We do not and probably will not have a safe effective tool like colonoscopy for screening. I'm not sure what the best resolution would be; in the ELCAP trial, they started with 10mm slices which is the television equivelent of a 13" black and white with rabbit ears. Higher resolution screening scans would allow earlier detection but will the price (financial, physical and emotional) justify the marginal improvement? Requires someone smarter than me to figure that out.

[Elaine]

Thank you so much for your response.

I don't understand the following paragraph very well:

They(CT) can't see the inside of hollow structures that well but once their have been a few branching of the bronchial system, the hollow tubes rapidly become microscopic anyways. Virtual bronchoscopy has few advantages over a high resolution CT scan except for the ability to see the interior architecture of the larger bronchi.

The first sentence I don't at all understand. In the second, what are the advantages over HRCT?

Thanks again.

Elaine