Dose optimization and indication of Linac radiosurgery for brain metastases

The authors have examined treatment effects of linear accelerator based radiosurgery for brain metastases. Optimal doses and indications were determined in an attempt to improve the quality of life for terminal cancer patients.

Ninety-two patients with 162 lesions were treated with Linac radiosurgery for brain metastases between April 1993 and September 1998. To determine prognostic factors, risk factors for recurrence, and appearance of new lesions, univariate and multivariate analyses were performed. To compare the local control between the high-dose (minimum dose > or =25 Gy: prescribed to the 50-80% isodose line) and low-dose (minimum dose <25 Gy) irradiated groups, matched-pairs analysis was performed.

Median survival time was 11 months. In univariate analysis, extracranial tumor activity (p<0.001) and Karnofsky Performance Status (KPS) (p = 0.036) were two significant predictors of survival. In multivariate analysis, the status of an extracranial tumor was the single significant predictor of survival (p = 0.005). Minimum dose was the single most significant predictor of local recurrence in univariate, multivariate, and matched-pairs analyses (p<0.05). As to the appearance of new lesions, activity of extracranial tumors was a significant predictor (p<0.05). Side effects due to radiosurgery were experienced in 4 of 92 cases (4.3%).

We concluded that brain metastases patients should be irradiated with > or =25 Gy, when extracranial lesions are stable and longer survival is expected. Combined surgery and conventional radiation may have little advantage over radiosurgery alone when metastatic brain tumors are small and extracranial tumors are well controlled. When extracranial tumors are progressive, the rate of appearance of new lesions in other nonirradiated locations becomes higher. In such cases, careful follow-up is required and a combination with whole brain irradiation should be considered.