Conference Vancouver, B.C. June 11, 2001
Speakers
Dr. Evans: So in summary, Simon here are the indications I think we should be using PET scanning in thoracic malignancy:
Dr Sutcliffe: Let’s go straight to the discussion of these indications and both yourself and Dr Baum put forward the evaluation of solitary or indeterminate Pulmonary Nodule. Can we now state that this now is state of the art practice, that it is the definitive investigation for the solitary pulmonary nodule?
Dr Coleman: I certainly think that it is an important study in the evaluation of the indeterminate nodule, Dr Evans asked well what do you do if the PET scan is negative, and I think that we still need to follow these nodules because the sensitivity in PET is not 100%, it is 95–97% sensitive so if the patient has an indeterminate nodule then one does need to follow this at 3 month intervals with a CT scan and that certainly is true if it is not ametabolic as Dr Baum showed some cases. If it is ametabolic my guess is the chances of that is zero but we don’t know that. So I think that these indeterminate nodules—you still need to follow, it is a small percentage, but you do need to follow them. Dr Evans mentioned that one of his cases was a bronchiole alveolus cell cancer—PET has a sensitivity of probably around 50 to 60% in bronchiole alveolus cell cancers and carcinoid tumours those are the two cell types where it is less accurate. Another observation is that we have been talking about non small cell lung cancer—that is where all the data is in the literature but those of us who do many PET scans are doing them for small cell lung cancer—it is elegant, it is extremely sensitive for detecting small cell lung cancer. The situation there is different than in non small cell lung cancer—limited versus extensive disease following therapy and I think that we will see the data expanded into small cell lung cancer in the future but for right now the data is on non small cell lung cancer.
Dr Shreve: I think there is one point to make about lung nodules is to say that PET is the definitive test is probably not the most accurate way to put it—it is one of the important tests, but it depends on the patient and the patient’s history, and the location and size of the nodule. Many times a large mass in a smoker where you pretest probability of cancer is probably 90% or better you are really going for histology as far as evaluating the mass. If you are doing a PET scan it is more for staging, than really evaluating a nodule that is almost certainly cancer so many of these patients present to us, and we are a referral centre, and that may have something to do with it, they present, already having a tissue diagnosis or at least one attempt at tissue diagnosis. So you have to look at PET in the context of the individual patient’s presentation. In some cases nodules are hard to biopsy because of peripheral or near the apex or in the diaphragm and then again PET would be probably be the definitive initial test to do but it all depends on the patient at presentation.
Dr Baum: Just one small comment. As I mentioned I think it is very important to do an interdisciplinary decision, it is not a decision by one modality or one clinical specialty, you really have to include your pulmologist, thoracic surgeon, I mean it is quite different from patient to patient if you have a 75 year old with a lot of risk factors it is much different from a 35 year old with no risk factors and probably in the last case we would more often be surgically aggressive, whereas in the other case we would be more conservative, so it is very important to for all.
Floor: Ken presented one case with an esophageal and a non small cell but what safeguards are there for multiple lung primaries for although it is not common, certainly we see patients that present with multiple lung primaries and one of the concerns could be that PET would overcall those as metastases?
Dr Coleman: Well certainly that is the case we can’t differentiate multiple simultaneous primaries from a metastatic lesion, but if we have a patient that does have two separate lesions, our surgeons will biopsy each, and not infrequently there will be the squamous cell and adeno that they are different, so depending on the situation and that is what Dr Baum was mentioning, you have to take the patient into consideration and look at all the information you have but simultaneous primaries do occur and just because we see lesions in opposite lungs does not necessarily mean that it is metastatic disease if we have a lesion, in both lungs and one in the adrenal and one bone then you have your answer but if you have just two focal lesions, simultaneous primaries certainly has to be considered.
Dr Lam: I would like to ask the panel if we have a negative PET scan, can we bypass a mediastinoscopy for staging prior to operation?
Dr Baum: For my perspective, yes if you compare the results by mediastinoscopy and by PET, it is clear-cut that PET is more sensitive than mediastinoscopy; I mean this is especially true for the left side for super aortic and para-esophageal lymph nodes and so you can hardly reach with mediastinoscopy, so if the PET scan is negative you can leave out the mediastinoscopy.
Dr Coleman: At our institutions most of the patients will still undergo mediastinoscopy—T1 lesions may not, if there is no evidence of adenopathy on the CT scan, but still most patients do undergo mediastinoscopy even following the PET scan T1 lesions with a negative PET may not.
Dr Conti: Our experience at USC is similar—most of those cases will go to mediastinoscopy, however I just want to mention a caveat; some cases where you have a hyper metabolic pulmonary lesion, and you may see mild uptake in the hilum mediastinum your tendency perhaps is to consider that as inflammatory process either because it doesn’t look similar to the primary tumour or because the pattern based on other ancillary findings suggest that it might be inflammatory, in several of those types of cases end up being metastatic disease and usually because it is very minimal the amount of tumour burden not necessary giving you the same presentation of level of activity that you might see in the primary so in those types of situations we usually take those patients to mediastinoscopy almost as a routine.
Dr Evans: I think Steve, that for any thing other than a T1 lesion that needs to be studied further with PET and mediastinoscopy.
Dr Lam: A question for Dr Baum please, one of your slides showed that PET was not useful for staging metastatic disease in the brain, could you clarify that a bit further especially if you suspecting or only expecting a solitary lesion—does it make a difference if it is only a single metastases in the brain? Is PET accurate enough to determine that?
Dr Baum: No, I don’t think that PET is useful in any way to look at brain metastases because sensitivity is just not high enough. So if you have a single lesion detected by MRI or multiple lesions it depends; usually it is not operated on in small cell lung cancer.
Dr Coleman: The problem with PET in the brain is the normal cortical uptake and seeing small metastases at the grey white junction, we just do not see. There have been several studies including one from Duke University that maybe 10–20% of patients that have brain metastases will you detect so it is a very small percentage that you do detect so most centres do not even include the brain as part of the whole body study because the sensitivity is so low.
Dr Sutcliffe: I am just going to go to another indication that would seem to be that in medically fit patients with non-small cell lung cancer, you have indicated for lymph node staging and also for exclusion of distant metastasis, i.e., defining the operable patient cure—Would you comment on that in the context of is that the state of the art statement now, is that where the practice is?
Dr Baum: I can comment from our centre, which has PET and I would fully agree on what you said for our Centre and I think for most of the centres collaborating with institutions having PET, having PET themselves. So for Germany yes. This is I think state of the art. Unfortunately about 60% of the patients are not operated in centres so in smaller hospitals or peripheral hospitals and in these institutions very often there is PET it is not available. So one must differentiate between what is really state of the art and what is clinical practice. I think that many of the patients still do not receive PET scanning in Germany before a lung operation.
Dr Coleman: Absolutely the primary value or one of the major values of PET is the staging of M disease, do these patients have distal metastatic disease? And PET has shown to be very accurate, more accurate than CT or bone scanning in detecting that—it certainly is the staging procedure of choice.
Dr Sutcliffe: Could you comment on detection of recurrence which Dr Baum you had indicated as one of your 1A recommendations in terms of putting that forward as an indication. Is that an across the board statement or is there any sub-distinction within that as to the use of PET?
Dr Baum: It is done mostly after an anatomic test such as CT which shows some alterations, which are not clear cut related to recurrence so in this situations yes, I think is a very good method. It has a very, very high sensitivity, coming from all studies that we looked at, and it is also very important for making the therapeutic decision as to what to do on a patient. Some patients you can still do local radiation therapy, if there are distant metastases, in addition to the recurrence, you probably better with chemo therapy and radiation therapy in some areas so it is very important for making the therapeutic management correctly using of PET in the recurrent situation.
Dr Sutcliffe: Presumably most specifically, when you consider patients for the surgery option?
Dr Baum: Yes, absolutely all the tests show that it also has a very high specificity especially in patients that have not been irradiated before.
Dr Sutcliffe: Any further comments from the floor for lung indications for PET? Yes.
Floor: I have a two part question actually—the first part pertains to image acquisition for radiotherapy planning and the second is about the coincidence option on gamma cameras. For radiotherapy planning is it your routine practice to acquire your PET scans in the treatment position? I notice that for most of the images that you presented the arms were down and presumably the treatment position we would have the arms raised. Ideally the CT and PET images would be acquired at the same visit, with the combined machine for that purpose, in treatment position but failing that for your routine initial staging would it be …. therapy planning and the second part of the question: For PET detection is there anything that is lost when you compare the dedicated PET?
Dr Baum: Maybe for the first part I would like to answer: Nothing is routine up to now for radiation planning therapy it is very much in academic environment and we are really looking and testing a lot of different approaches to see what is the best for image fusion. What you have to keep in mind and one is of course the position of the patient and I mentioned the breathing is very important and we now have software available that runs on a nuclear diagnostics workstation where you can very nicely by software interpolate the images and do the image fusion process so these things like arms up and down is not so much important if you are using clearly for the purpose of radiation therapy. Planning should of course be as much similarity between the two studies as possible. The second question I would like to pass on to Dr Coleman.
Dr Coleman: Yes, I agree with Professor Baum concerning if you are going to be doing these studies for primarily radiation therapy you may want to use the same bed, curve bed, flat bed, you may want to use the cradle arm or the head down whatever is going to be done for therapy planning that certainly would facilitate the fusion and making sure that the therapy volumes were appropriate. Concerning camera based PET versus Dedicated PET for therapy planning: you are going to have more accurate localization of the FDG with the dedicated scanner when they are compared to the camera based PET. With the camera based PET you can detect lesions you cannot detect as small a lesion as you can with the dedicated PET scanner that is the camera based PET will not detect the small lesions as will the dedicated scanner and furthermore the edges are going to be blurrier with the camera based PET than with the dedicated PET—you will have more accurate localization because of the higher resolution with the dedicated PET compared to the camera based PET.
Dr Wahl: One further caveat with the camera based PET methods. If you don’t use attenuation correction with the coincidence option then you will also have anatomic distortions which can make matching the shape of the thorax difficult so I think that most of the efforts with treatment planning have focused on dedicated PET where the body outlines are preserved with the same geometric ratios. Without attenuation correction the tumours can be distorted often lengthened in the anterior posterior dimension and as I have said the edges blurred, in some cases cericallesions can look a little like cigars so there are really some cautions in addition to the difficulty in seeing the smaller lesions with a coincidence system—especially with the earlier ones that were on the market.
Dr Conti: One other comment that I would also like to make is that as a result of this meeting today you are going to be flooded with referrals for PET scans of course and the throughput from the coincidence cameras is significantly slower than the dedicated PET.