Radiosurgery is regarded as a standard therapy for the metastatic brain tumors. However, failure of the radiosurgery which needs a repeated therapy to the same lesion is still an unsolved problem to improve the outcome of the metastatic brain tumors.

     We analyzed the outcome of the gamma knife radiosurgery (GKRS) for the metastatic lesions to identify factors leading to the treatment failure.

     We analyzed 86 patients with metastatic brain tumors who were treated in our hospital and followed more than 6 months. In a total of 86 patients, male were 47 and female 34. Primary sites were the lung (n=50), breast (n=11), colon (n=6), kidney (n=5), rectum (n=3), and others (n=11). Median survival time was 36 months.

     Treatment failure was defined as lesions regrowing or requiring repeated GKRS within 6 months. For multiple lesions, the largest mass was evaluated. The primary site, metastatic location, Karnofsky scale, tumor size, number of metastatic lesions, and various quality parameters of the prescription (QPP) were analyzed. Evaluated QPPs were the conformity index (CI) of Paddick, RTOG-CI, and gradient index.

     After exclusion of patients who died within 6 months due to systemic lesions, fourteen out of 77 lesions were regarded as treatment failure. The lung cancer as a primary site had a lower failure rate than the breast cancer and renal cell carcinoma (p<0.05). Lesions with a high CI of Paddick or low RTOG-CI had a higher rate of treatment failure (p<0.05). Multivariate analysis revealed that the tumor site and CI of Paddick were related to the treatment failure (p<0.05).

     This is a retrospective study.

     According to our results, renal and breast cancers had higher rate of treatment failure than lung cancers.

     For the planning of the radiosurgery, CI of Paddick needs to be considered to reduce the treatment failure.