Here's some other excerpts:
"Serial MR studies of unilateral vestibular
schwannomas treated with gamma knife radiosurgery
showed that temporary enlargement of tumor
occurred in 41% of cases. Temporary enlargement
occurred mostly within the first 2 years after radiosurgery."
Full text: http://www.ajnr.org/cgi/reprint/21/8/1540.pdf
Thanks so much for sharing this research with us, JB. I followed the link and read the entire report. Here are some of my observations:
1. There are 4 charts shown (I would post the other two, but I don't know how to copy and paste them into a post). The two charts and accompanying analysis not included in JB's post show continuous tumor enlargement (i.e., that which did not shrink after enlarging) in 12% of patients in the study and alternating enlargement and regression (shrinking) in 13%. Taken together with the 41% who exhibited temporary enlargement, this brings the percentage total of all swellers post-CK treatment to 66% in this study. It is important to realize that only 61 patients are included in the charts, however, so this is a relatively small study compared to others of its kind (and therefore has a larger margin or error). While 78 patients had follow-up MR studies, only the 61 who are included in the charts had *serial* MR studies (more than one followup MRI).
2. The report is a bit sloppy, IMHO. The first page of the report states, "Follow-up MR studies were obtained between 10 and 63 months (mean, 34 months) after treatment." Yet, the 4 charts all show the vast majority of the patients received their first follow-up MRI within about 6 months of treatment. Also, tumor volume for patients included in the study is cited to have "varied from 0.2 to 20.1 mm
3." Taken literally, this would mean the tumors would have to have all measured under 3 mm in all three dimensions on average. I think the authors probably meant to say that maximum tumor dimension on any one axis varied from 0.2 to 20.1 mm, in which case this study excluded large tumors measuring over 2 cm. I have heard Japanese studies of vestibular schwannomas criticized elsewhere as constituting "sloppy work," casting doubt on their accuracy. I have never before seen any reason to support that criticism, but this report left me suspicious.
3. This report spans a period from 1991 to 1996. Technological advances in computerized dose planning and MR imaging over the past 10 years might yield better results in patients receiving GK treatment today.
4. It appears as if the charts each show one segmented line for each patient included in the study of serial-MR results. But it's important to realize that the text of the study also reports on results of those patients who had only one follow-up MRI, and not a series of follow-up MRIs. This larger group (serial + one-time follow-up MRIs) constituted 78 patients. In this group, the rate of tumor control was cited to be 81%. The report later states, "IN OUR SERIES [my emphasis], the tumor control rate was 81%." Again, sloppy work because the charts show only 11% of the patients who had serial follow-up MRIs had continuous (not temporary) enlargement. A tumor control rate of 89% is more in line with that reported in other GK studies, such as Flickinger et al (89% tumor control rate) and Noren et al (88%); both of those studies occured in the early- to mid-90s.
5. The report also concluded that "a transient loss of contrast enhancement does not necessarily predict subsequent tumor regression." In other words, dark spots in the tumor showing on the MRI do not necessarily predict a tumor will shrink in size. A study by Linskey, Lunsford and Flickinger in 1990 concluded, however, that transient loss of contrast enhancement was found to be a good prognostic indicator of tumor regression, so the jury is out on this point.
In conclusion, this is an interesting bit of research and I'm really grateful that JB brought it to our attention. But, in light of the sloppy reporting contained therein, I for one am taking it with a grain of salt.
I know of no other studies quantifying tumor swelling post-GK treatment. But Dr. Chang told me last week that the chance of my tumor swelling after *CyberKnife* treatment is only 25%. CyberKnife (CK) is a different type of radiosurgery from GK. CK has a shorter track record, as it's only been approved by the FDA since 1999 (although Stanford has used it since 1994 in clinical trials). One of the perceived advantages of CK over GK is that the dosage of radiation is applied more homogeneously throughout the entire tumor. Dosage at the center of the tumor is only 15% higher than at the periphery, as opposed to double (100% greater) dosage at the center compared to at the periphery for GK. FWIW, this is one of the key reasons I have decided to get CK instead of GK, as I feel that my chance of tumor swelling are less if no part of the tumor receives more radiation than it needs to kill it (reducing collateral damage to nearby healthy tissue). I also like that CK is non-invasive, delivers fractionated doses (which some research indicates preserves hearing better than getting one huge dose) and can be repeated.
Tumbleweed
