ESTRO 2023 - Abstract Book

S538

Sunday 14 May 2023

ESTRO 2023

Twelve patients of median age 65 years (41-77) were recruited between 11/2020 and 02/2022. 3/12 had synchronous BMs. Seven patients had a single BM, four had two BMs, and one had three BMs. 11/12 patients received preoperative radiosurgery and metastasectomy as intended. The twelfth patient went directly to surgery and received postoperative fractionated stereotactic radiotherapy (fSRT). The median time between referral and radiosurgery was 5.5 working days (1-10) and neurosurgery took place a median of 1 day later (0-5), thus the median time from tumour board to metastasectomy was 7.5 working days (2-10). The median encompassing dose was 16 Gy (14-19), median GTV was 9.6 cm3 (7.0-21.5) and median PTV was 12.7 cm3 (5.9-26.1). 5/11 patients who received preoperative radiosurgery have completed 12 month follow-up without local recurrence or leptomeningeal disease. There was one acute related toxicity (grade 2 alopecia) at 3 months which recovered fully by 6 months, and seven patients have died from extracranial causes. The patient who received postoperative fSRT developed a small leptomeningeal recurrence 3 months after metastasectomy. Conclusion Preoperative SRS was feasible in 11/12 patients and safe in 11/11 patients. This protocol constitutes the experimental arm of an open, international randomised trial to compare the efficacy of preoperative radiosurgery against postoperative hypofractionated stereotactic radiotherapy (PREOP-2, NCT05124236). PD-0646 Outcomes of stereotactic radiosurgery for colorectal cancer brain metastases C. Gui 1 , K.D. Mueller 1 , J.E. Eichholz 2 , H. Walch 2 , I. Khatri 1 , L. del Balzo 1 , N.E. Kemeny 3 , B.S. Imber 1 , N. Schultz 4 , M.B. Foote 3 , R.D. Yaeger 3 , L.R.G. Pike 1 1 Memorial Sloan Kettering Cancer Center, Department of Radiation Oncology, New York, New York, USA; 2 Memorial Sloan Kettering Cancer Center, Sloan Kettering Institute, New York, New York, USA; 3 Memorial Sloan Kettering Cancer Center, Department of Medicine, New York, New York, USA; 4 Memorial Sloan Kettering Cancer Center, Department of Epidemiology and Biostatistics, New York, New York, USA Purpose or Objective Brain metastases (BM) from colorectal cancer (CRC) are rarely observed and portend a poor prognosis. Stereotactic radiosurgery (SRS) remains a mainstay in treating CRC BM when the burden of intracranial disease is low. This study evaluated the oncologic outcomes and prognostic factors after SRS for CRC BM. Materials and Methods Patients with newly diagnosed CRC BM treated with SRS alone or postoperative SRS to the resection cavity at a single institution between 2009 and 2022 were included. Patients who received whole-brain radiation therapy as part of initial treatment were excluded. To enable forthcoming genomic analyses, this cohort was limited to patients with genomic profiling of at least one intracranial or extracranial tumor. Overall survival (OS), intracranial progression-free survival (iPFS), local recurrence (LR), and baseline characteristics of the patient, disease, and SRS were obtained from clinical notes and contrast-enhanced MRI brain. Kaplan-Meier modeling, logistic regression, and Cox regression were used in the analysis. Genomic profiling was performed with one of four versions (341, 410, 468, or 505-gene) of MSK-IMPACT, a custom FDA-approved hybrid-capture sequencing assay. Results This study included 124 patients with 304 CRC BM. Sixty-one patients (49%) had rectal cancer. At BM diagnosis, the median age was 56 years (range 25-91). The median number of BM per patient and median BM size were 2 (range 1-16) and 1.1 cm (range 0.2-5.5), respectively. Sixty-six BM (22%) received postoperative SRS. The median prescription was 27 Gy (range 16- 30) in 3 fractions (range 1-5), and the median biologically effective dose (BED, α / β = 10) was 51.3 Gy (range 35.7-73.3). Median OS and iPFS were 7 months (95% CI 5.0-12) and 3 months (95% CI 2.5-3.9), respectively. On multivariable Cox regression, OS was longer in patients with better Karnofksy Performance Status (HR=0.97, p=0.004) and worse in patients with liver metastases (HR=2.1, p=0.001) and ≥ 3 sites of extracranial disease (HR=2.8, p<0.0001). These factors were also associated with iPFS (p<0.05). Intracranial progression alone was associated with the initial number of BM (HR=1.1, p=0.01) and progressive extracranial disease (HR=2.65, p=0.01). There were 20 cases of LR at median 2.8 months. On univariable logistic regression, greater PTV volume and BED < 51.3 Gy were associated with increased LR at 6 months. On multivariable regression, only BED < 51.3 Gy was significant (OR=4.5, p=0.02). All patients had at least one sample for MSK-IMPACT analysis. Associations between genomic features and CNS- specific outcomes are forthcoming.