**10. Local experience**

Our centre, the Queen Elizabeth Hospital in Hong Kong, have conducted a 10-year review of the patients who received LINAC-based SRS or SRT for intracranial meningioma from July, 2009 to June, 2019. We investigated the tumor control rate in the 1-, 2- and 5-years intervals. Tumor control was defined as a static or shrunken tumor. Functional outcome was determined by modified Rankin scale (mRS).

40 patients were included with 45 tumors irradiated. 42% of the tumors were parasagittal or parafalcine, followed by 20% petrous or petroclival and 18% convexity. 48% of the tumors were WHO grade I while 52% were WHO grade II. In 48% of the cases, Simpson I/II excision was achieved while in the remainder, Simpson III/ IV was achieved. In 27% of the tumors, radiosurgery were done as primary treatment while 73% as postoperative adjuvant treatment.

In the recent 25 cases, we switched from frame-based to frameless radiosurgery, using the LINAC system. Mean radiation dose was 22.4Gy (SD: 7.2). Mean target volume was 5.0 (SD: 6.1) while mean treatment volume was 6.0 (SD: 6.8), with mean treatment-target ratio being 1.8 (SD: 1.0). Mean coverage was 96.3%. Mean conformity index was 1.7 (SD: 1.0).

Tumor control rate was achieved in 82%, 79% and 66% in 1-, 2- and 5-years intervals respectively. More than 80% patients enjoyed mRS 0–1 over the study period. SRS was associated with better tumor control in the 1- and 2-years interval compared with SRT. However, it was confounded by smaller target volume. Other teletherapy metrics were found to have no significant association with the outcome.

11% of the patients required reoperation, while 7% developed radionecrosis or radiation-induced edema. Multiple meningiomata was associated with poor tumor control in 5 years (20% vs. 82%, p=0.025). It may reflect the underlying pathology of the entire intracranial meninges, making local irradiation ineffective in overall intracranial control. Parasagittal or parafalcine locations predicted reoperation (21% vs. 0%, p=0.026). We observed that these tumors more likely recurred and caused symptoms which required surgical decompression. On the other hand, tumors inside the superior sagittal sinus were often not removed in operation. The residual tumors may progress, with nurture by the surrounding vasculature. Moreover, sometimes there is technical difficulty to plan effective radiation dose to cover the adequate dura origin in this location.

Overall, neither histology grading nor the extent of resection predicted tumor control rate when they were analyzed as ordinal scale in our study.
