Purpose: To investig
ate the need of
a m
argin other th
an for
accur
acy re
asons in stereot
actic r
adiosurgery (SRS) of br
ain met
ast
ases by me
ans of histop
athology.
Methods and Materials: Evaluation of 45 patients from two pathology departments having had brain metastases and an autopsy of the brain. Growth patterns were reviewed with a focus on infiltration beyond the metastases boundary and made visible with immunohistochemical staining: the metastasis itself with tumor-specific markers, surrounding normal brain tissue with a glial marker, and a possible capsule with a soft tissue marker. Measurements were corrected by a tissue-shrinkage correction factor taken from literature. Outcomes parameters for infiltration were mean and maximum depths of infiltration and number of measured infiltration sites.
Results: In 48 of 76 metastases, an infiltration was present. The largest group of metastases was lung cancer. Small-cell lung cancer (SCLC) and melanoma showed a maximum depth of infiltration of ≥1 mm, and other histologies <1 mm. For non–small-cell lung cancer (NSCLC), melanoma, and sarcoma, the highest number of infiltrative sites were observed (median, 2; range, 1–8). SCLC showed significantly larger infiltrative growth, compared with other diagnostic groups. In NSCLC, the highest percentage of infiltration was present (70 % ).
Conclusions: Infiltrative growth beyond the border of the brain metastasis was demonstrated in 63 % of the cases evaluated. Infiltrative growth, therefore, has an impact in defining the clinical target volume for SRS of brain metastases, and a margin of 1 mm should be added to the visible lesion.
