A new prognostic instrument to predict the probability of developing new cerebral metastases after radiosurgery alone

BACKGROUND: Addition of whole-brain irradiation (WBI) to radiosurgery for treatment of few cerebral metastases is controversial. This study aimed to create an instrument that estimates the probability of developing new cerebral metastases after radiosurgery to facilitate the decision regarding additional WBI. METHODS: Nine characteristics were investigated for associations with the development of new cerebral metastases including radiosurgery dose (dose equivalent to <20 Gy vs. 20 Gy vs. >20 Gy for tumor cell kill, prescribed to the 73-90% isodose level), age (≤60 vs. ≥61 years), gender, Eastern Cooperative Oncology Group performance score (0-1 vs. 2), primary tumor type (breast cancer vs. non-small lung cancer vs. malignant melanoma vs. others), number/size of cerebral metastases (1 lesion <15 mm vs. 1 lesion ≥15 mm vs. 2 or 3 lesions), location of the cerebral metastases (supratentorial alone vs. infratentorial ± supratentorial), extra-cerebra metastases (no vs. yes) and time between first diagnosis of the primary tumor and radiosurgery (≤15 vs. >15 months). RESULTS: Number of cerebral metastases (p = 0.002), primary tumor type (p = 0.10) and extra-cerebral metastases (p = 0.06) showed significant associations with development of new cerebral metastases or a trend, and were integrated into the predictive instrument. Scoring points were calculated from 6-months freedom from new cerebral metastases rates. Three groups were formed, group I (16-17 points, N = 47), group II (18-20 points, N = 120) and group III (21-22 points, N = 47). Six-month rates of freedom from new cerebral metastases were 36%, 65% and 80%, respectively (p < 0.001). Corresponding rates at 12 months were 27%, 44% and 71%, respectively. CONCLUSION: This new instrument enables the physician to estimate the probability of developing new cerebral metastases after radiosurgery alone. Patients of groups I and II appear good candidates for additional WBI in addition to radiosurgery, whereas patients of group III may not require WBI in addition to radiosurgery.