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MO_12_2786 - Comparison of Local Failure and Radionecrosis According to Dose Prescription for Small to Medium Sized Brain Metastasis treated with Radiosurgery

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

Comparison of Local Failure and Radionecrosis According to Dose Prescription for Small to Medium Sized Brain Metastasis treated with Radiosurgery
F. Y. Moraes1,2, J. Winter2, E. Atenafu3, A. Dasgupta1,2, C. Coolens2, B. A. Millar1,2, N. J. Laperriere1,2, D. S. C. Tsang1,2, M. Bernstein4, P. Kongkham4, G. Zadeh4, T. D. Conrad1,5, A. Berlin1,2, and D. B. Shultz1,2; 1Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada, 2Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, 3Department of Biostatistics, University Health Network, University of Toronto, Toronto, ON, Canada, 4Department of Neurosurgery, Toronto Western Hospital - University of Toronto, Toronto, ON, Canada, 5Radiation Medicine Program, University Health Network and Princess Margaret Cancer Centre, Toronto, ON, Canada

Purpose/Objective(s): To examine the impact of gamma knife radiosurgery (SRS) marginal prescription dose (PD) (15 Gy vs. 16-20 Gy vs. > 20Gy) on local failure (LF) and radionecrosis (RN) for small- to medium-sized (≤ 2 cm) brain metastasis (BM) in a large single-institution series.

Materials/Methods: We identified patients from a prospective registry of BM patients treated with SRS between 2006 and 2017. At our institution, we commonly treat lesions adjacent to eloquent structures with a lower PD to reduce the likelihood of toxicity. We used defined criteria to differentiate LF from RN, including pathology, when available. Cumulative incidences of LF and RN were calculated using Fine and Gray’s competing event analysis, with death as a competing event. Patient, tumor, and treatment factors were assessed for their impact on LF and RN.

Results: We reviewed 462 patients with 1609 BM ≤2 cm. Lung (51.1%), melanoma (14.3%) and breast (13.9%) were the most common primary histology. Sixty percent of the patients received pre or post-SRS (including salvage) whole brain Brain radiotherapy. Median overall survival and radiographic follow-up was 19.7 months (95%CI 17.4 to 23.3 months and 13.4 months (IQR 7.9-22.4 months), respectively. 1065 lesions (66%) were treated with PD >20 Gy, 80 lesions (5%) with 16-20 Gy and 464 lesions (29%) with <15 Gy. Cumulative LF rates at 2 years were 15.2% (95%CI 6.2-24.3%) for 15 Gy, 11.9% (95%CI 0-29.5%) for 16-20 Gy, and 6.4% (95%CI 2.2-10.6%) for >20Gy (p<0.0001). Cumulative RN rates at 2 years were 5.5% (95%IC 0-11.6%) for 15 Gy, 6.2% (95%CI 0-17.9%) for 16-20 Gy and 6.4% (95%CI 2.4-10.3%) for >20Gy (p=0.2381). Tumor size ≤ 1 cm was associated with a significantly lower rate of LF (HR 0.318 (95%CI 0.216-0.468; p<0.0001) and RN (HR 0.194 (95%CI 0.120-0.314; p<0.0001) compared to BM > 1 cm. Cumulative LF and RN rates at 2 years for lesions ≤ 1 cm was 4.7% (95%CI 0.08-8%), and 2.6% (95%CI 0-5.4%), respectively. Cumulative LF and RN rates at 2 years for lesions were > 1 cm was 15.3% (95%CI 8%-22%) and 11.8% (5.1-18.5%), respectively. For lesions > 1 cm, LF occurred in 9.5% vs. 5% of tumors treated with 15 Gy and >20 Gy, respectively (p=0.0003). There was a significantly increased risk of RN for lesions >1 cm treated with >20 Gy vs. 15 Gy (6.10% versus 3.23%; p=0.0011).

Conclusion: Our results suggest that for BM >1 cm treated with SRS, 15 Gy provides inferior local control compared to> 20 Gy, but is associated with a lower rate of RN. For lesions ≤ 1 cm, LF and RN incidences are both < 5%.

Author Disclosure: F. Moraes: None. E. Atenafu: None. A. Dasgupta: None. C. Coolens: Patent/License Fees/Copyright; Modus Medical. N.J. Laperriere: None. M. Bernstein: None. G. Zadeh: None.

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