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Use
of the RTOG recursive partitioning analysis to validate the benefit of
iodine-125 implants in the primary treatment of malignant gliomas
Videtic
GM, Gaspar LE, Zamorano L, Fontanesi J, Levin KJ, Kupsky WJ, Tekyi-Mensah S
Department
of Radiation Oncology, London Regional Cancer Centre, University of Western
Ontario, Canada. gvidetic@lrcc.on.ca
Purpose.
To date, numerous retrospective studies have suggested that the addition of
brachytherapy to the conventional treatment of malignant gliomas (MG) (surgical
resection followed by radiotherapy +/- chemotherapy) leads to improvements in
survival.
Two randomized trials have suggested either a positive or no survival benefit
with implants.
Critics of retrospective reports have suggested that the improvement in patient
survival is due to selection bias.
A recursive analysis by the RTOG of MG trials has stratified MG patients into 6
prognostically significant classes.
We used the RTOG criteria to analyze the implant data at Wayne State University
to determine the impact of selection bias.
Methods
and Materials. Between July 1991 and January 1998, 75 patients were treated with
a combination of surgery, radiotherapy, and stereotactic I-125 implant as
primary MG management.
Forty-one (54.7%) were male; 34 (45.3%) female.
Median age was 52 years (range 4-79).
Twenty-two (29.3%) had anaplastic astrocytoma (AA); 53 (70.7%), glioblastoma
multiforme (GBM).
Seventy-two patients had data making them eligible for stratification into the 6
RTOG prognostic classes (I-VI).
Median Karnofsky performance status (KPS) was 90 (range 50-100).
There were 14, 0, 14, 31, 12, and 1 patients in Classes I to VI, respectively.
Median follow-up time for AA, GBM, and any surviving patient was 29, 12.5, and
35 months, respectively.
Results.
At analysis, 29 (40.3%) patients were alive; 43 (59.7%), dead.
For AA and GBM patients, 2-year and median survivals were: 58% and 40%; 38 and
17 months, respectively.
For analysis purposes, Classes I and II, V and VI were merged.
By class, the 2-year survival for implanted patients compared to the RTOG data
base was: III--68% vs. I--76%; III--74% vs. 35%; IV--34% vs. 15%; V/VI--29% vs.
V--6%.
For implant patients, median survival by class was (in months): I/II--37;
III--31; IV--16; V/VI--11.
Conclusion.
When applied to MG patients receiving permanent I-125 implant, the criteria of
the RTOG recursive partitioning analysis are a valid tool to define
prognostically distinct survival groups.
As reflected in the RTOG study, a downward survival trend for the implant
patients is seen from "best to worse" class patients.
Compared to the RTOG database, median survival achieved by the addition of
implant is improved most demonstrably for the poorer prognostic classes.
This would suggest that selection bias alone does not account for the survival
benefit seen with I-125 implant and would contradict the notion that the
patients most eligible for implant are those gaining the most benefit from the
treatment.
In light of the contradictory results from two randomized studies and given the
present results, further randomized studies with effective stratification are
required since the evidence for a survival benefit with brachytherapy (as seen
in retrospective studies) is substantial.
PMID:
10524423 [PubMed - indexed for MEDLINE]
Source:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10524423&dopt=Abstract |
