P03.02 Risk of leptomeningeal dissemination in patients treated with postoperative stereotactic radiotherapy of brain metastases

Abstract

Abstract Background There is a body of evidence that the risk of leptomeningeal dissemination (LMD) is increased in the postoperative stereotactic radiotherapy (SRT) of brain metastases (BM) compared to adjuvant whole brain radiotherapy (WBRT). The proposed mechanism is an iatrogenic tumor dissemination into the cerebrospinal fluid at time of surgery. Including a wider volume of meningeal wall and the entire surgical track in the definition of the postoperative SRT clinical target volume (CTV) to decrease LMD is still controversial. The aim of this study was to retrospectively analyze the outcome of adjuvant SRT targeted at resection cavities of BM without previous WBRT. MATERIAL / METHODS We reviewed 70 patients treated with postoperative SRT for BM. Stereotactic planning computed tomography and planning MRI were imported into iPlan RT image software for image registration and TV delineation. The CTV consisted of any residual enhancement and all resected cavity including a safety margin of 1 to 2 mm. Only in cases of superficial initial tumor with meningeal contact was the CTV enlarged to the adjacent meningeal wall, but never included edema or the entire surgical track. Patients underwent regular follow-up MRI. The cumulative incidence rates of LMD was retrospectively calculated as well as patterns of failure. RESULTS The most common histological type was non small cell lung cancer in 61.4%. There were 38.6% infratentorial locations and 37.2 % superficial lesions. En bloc resection was achieved in 60% and compete resection in 75.7%. After a median imaging follow up time of 16.7 months, 54.3% of patients experienced distant brain failure. LMD occurred in 9 of 70 patients (12.9 %) at a median time of 10.7 months. Survival without LMD was 88% at 1 year (IC 95% 79%-97%) and 82% at 2years (IC 95% 72%-94%). In three quarter of cases, LMD interested superficial lesions. In univariate analysis, survival rates without LMD at 1 year for superficial and deep lesions were 88 % and 94 %, respectively (p=0.49). We report only one recurrence in the surgical track (1.42%). CONCLUSION The risk of LMD was comparable to the literature (11–17%). Superficial lesions were slightly more likely to relapse in the meninges, but it was non-significant. The risk of recurrence in the surgical track is negligible. Our results do not support the current guidelines recommending the systematic inclusion of the surgical track and the related meninges in the CTV.