Central Nervous System

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MO_7_2625 - Spine stereotactic radiosurgery offers excellent local control in patients with bulky spinal disease

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Spine stereotactic radiosurgery offers excellent local control in patients with bulky spinal disease
F. Kazmi1, K. L. M. Chua2, M. L. K. Chua2, F. Y. Wong2, E. T. Chua2, A. Thiagarajan2, J. H. Phua2, K. P. Chan2, and E. L. Soon1; 1National Cancer Centre, Singapore, Singapore, 2National Cancer Centre Singapore, Singapore, Singapore

Purpose/Objective(s): Spine radiosurgery (SRS) delivers ablative radiotherapy for optimal local control of bony disease. While results from de novo treated small volume bony metastases demonstrate superior outcomes to conventional radiotherapy, concern surrounds the use of spine SRS in bulky lesions with multi-level, para-spinal and epidural components due to concerns regarding toxicity, particularly if irradiated prior. We hypothesize that spine SRS will deliver excellent outcomes even in these bulky aggressive lesions.

Materials/Methods: We performed a retrospective review of treatment outcomes for patients with biopsy proven metastatic disease from 2012 to 2017 who underwent SRS to bulky bony metastases, defined as lesions with multiple (≥2) level involvement, para-spinal and epidural components. To account for different dose fractionations, biological equivalent doses in 2 Gy fractions (EQD2) using α/ßTumour = 10 and α/ßcord = 2 were used. Response was assessed on serial MRI/CT imaging every 3-4 mo, following SPINO guidelines and toxicities were prospectively recorded using CTCAEv4. Kaplan-Meier was performed and survival outcomes compared using log-rank test.

Results: We identified 32 patients with 38 bulky lesions; 14 para-spinal disease, 20 epidural, 8 multi-level disease. Median age was 62 yo (IQR: 52 – 69). Median follow up was 5.3 mo (IQR: 2.0 – 20.9). Majority of histologies include renal (13), prostate (5) and Nasopharynx (5). 15 (39.5%) patients had oligometastatic disease. Of the 38 lesions, 13 (34.2%) had prior surgery, 14 (36.8%) had prior RT (24-50Gy in 1.8-12Gy fractions), including 2 lesions treated by prior spine SRS 24Gy in 12 Gy fractions. Median dose of SRS was 24Gy (24 – 30Gy) in 12 (6.75 – 12) Gy fractions. The median EQD2(10) received by 95% and 10% of the PTV_eval (2mm PTV expansion with subtraction of cord prv) was 31.3Gy (27.8 – 37.7) and 56.5Gy (45.8-63.2) respectively. Despite our cohort of bulky lesions, local control (LC) was excellent with 92.1% at 1 year. In pre-irradiated lesions, LC was 87.5% at 1 year. 2 patients (5.3%) had vertebral compression fracture post SRS with no documented disease relapse while 1 patient had a severe pain flare 2 days post SRS. No cord myelopathy was recorded. Median cord EQD2(2) D0.03cc was 37.5Gy (30.3- 42.9) for single course of RT and cumulative EQD2(2) D0.03cc was 43.4Gy (31.3- 55.46) for 2 courses of RT (median interval between RT = 17mo). Improved local control was demonstrated in patients with D95 EQD2(10) ≥35Gy (duration of LC: median 33.6mo vs 21.2mo, p = 0.5) suggesting that adequate coverage of the tumour by a tumoricidal dose is crucial. Interestingly, one patient with oligometastases on concurrent anti-PDL1 checkpoint blockade experienced an abscopal response in an unirradiated brain tumour.

Conclusion: Our data suggests that spine SRS offers excellent outcomes with minimal toxicities in this cohort of patients with bulky, vertebral metastases.

Author Disclosure: F. Kazmi: None. K.L. Chua: Honoraria; Varian Medical Systems. Consultant; National Cancer Centre Singapore. Co-Chair Neuro Oncology Cancer Service Workgroup; National Cancer Centre Singapore. M.L. Chua: None. F. Wong: None. A. Thiagarajan: None.

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