Evaluating the DS-GPA in patients with 1-10 brain metastases treated with stereotactic radiosurgery

Purpose or Objective
There are multiple prognostic models for predicting
survival after treatment for brain metastases. One of
them, the diagnosis-specific Graded Prognostic
Assessment (DS-GPA), has been developed to predict the
median survival for brain metastases from the most
frequent primary sites. Our objective is to compare the
survival predicted by the DS-GPA to actual survival in
patients treated with SRS for 1-10 brain metastases. We
will both evaluate the ability of the DS-GPA to predict the
survival on an individual level, as well as its success in
dividing a group of patients into different prognostic
strata.
Material and Methods
We identified a consecutive cohort of patients treated
with SRS for brain metastases in our institute. DS-GPA
scores were calculated for each patient, and the median
survival for each DS-GPA group was calculated.
Differences in survival between DS-GPA groups were
tested with Kaplan-Meier curves.
Results
Out of a total of 401 patients treated with SRS from 2012-
2017, 366 patients with calculable DS-GPA were
identified. Waterfall plots showing the difference
between predicted median and actual survival per patient
are shown in Figure 1, stratified by the number of brain
metastases. The proportion of the survival times within
each predicted quartile was 26.6%, 30.7%, 24.9% and 17.8%
(for Q1-Q4, respectively). Figure 2 shows the Kaplan-Meier
curves of the disease groups with a statistically significant
difference between the DS-GPA strata.
Conclusion
DS-GPA seems to be a reliable tool for brain metastases
patients treated with SRS. Although the differences
between the predicted median and the actual survival
difference can be large, the distribution of the actual
survival within the predicted quartiles is as expected. This
means that, although the DS-GPA doesn’t give a point
prediction of survival, it is able to accurately predict the
range in which the survival will fall.
Furthermore, the DS-GPA is also useful in dividing the
renal cell carcinoma, melanoma and both NSCLC disease
groups into strata with different survival. This allows
physicians to place a patient in a certain prognostic group,
which may help to determine the most optimal treatment
and the duration and frequency of follow-up.
The way physicians and other health professionals discuss
the results of the DS-GPA score is important. The fact that
it results in a median survival and not a point-predicted
survival is an important distinction. Patients should not be
told that the DS-GPA gives a precise prediction of the
expected survival. Instead, a patient needs to be told that
around half of the patients with similar clinical
characteristics reach the median age, but that the other
half dies before that time. This corresponds with our
findings. Additionally, the window of survival that applies
to half of the patients, i.e. the interquartile range, is
another important message for patients, which is also
something we have found in this study.