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Objective: We sought to determine the risk of leptomeningeal disease (LMD) in patients treated with stereotactic radiosurgery (SRS) targeting the postoperative cavity following surgical resection of a brain metastasis, deferring whole brain irradiation (WBRT) in all patients. Methods: We retrospectively reviewed 175 brain metastasis resection cavities in 165 patients with evaluable follow-up imaging treated with post-operative SRS from 1998 to 2011. No patient had WBRT. LMD was defined through radiologic and/or pathologic findings. The local cavity, distant parenchymal brain, and leptomeningeal brain failure rates were calculated using the competing risk analyses, with death as a competing risk. Control rates were censored at the time of last follow-up or at the time of salvage WBRT. Factors associated with LMD were determined through univariate analysis. The overall survival rate was calculated using Kaplan-Meier estimates. Results: Median follow-up duration was 12 months (range, 1 - 156 months). Median overall survival was 18 months. The cumulative incidence rates of local cavity failure at 1- and 2- years were 10% and 14%, respectively. Twenty-one patients (13% crude rate) developed LMD at a median of 5 months (range, 2-33 months) following SRS. The 1- and 2- year cumulative incidence rates of LMD were 11% and 13%, respectively. Posterior fossa (p=0.5) or pial (p=0.2) location was not associated with LMD. The factors predictive for LMD on univariate analysis were new parenchymal metastases (p=0.009) and breast cancer histology (p=0.004). Both continued to be significant on multivariate analysis (p=0.03 and 0.007, respectively). The 1 year rate of LMD was 24% for breast (n=26 patients) vs. 9% for non-breast (n=139) histology. The receptor status of breast cancer patients did not correlate with risk of LMD. All LMD patients were subsequently treated with WBRT. Median survival following the diagnosis of LMD was 7 months (range, 1 - 37 months). Conclusions: Patients treated with SRS targeting the post-operative cavity following resection of breast cancer metastases have a higher risk of LMD in this series. Whether the inclusion of WBRT would decrease the rate of LMD or if the biology of breast cancer brain metastases places patients at higher risk irrespective of the treatment choice is unknown. We encourage all future reports on SRS cavity boost to include the risk of LMD. Disclosure: No significant relationships. [ABSTRACT FROM AUTHOR]

Stereotactic body radiotherapy (SBRT) is increasingly being used to treat oligometastatic cancers, but high-level evidence to support policy decisions is lacking in patients with colorectal carcinoma (CRC). The purpose of this study was to determine the prognostic factors for survival in oligometastatic colorectal cancer patients treated with SBRT in a multicentric setting. The clinical data of 437 oligometastatic CRC patients who received metastasis directed treatment (MDT) via SBRT at 18 institutions between February 2007 and February 2021 were reviewed retrospectively. Patients either had de novo oligometastasis (≤5 metastases) at the time of diagnosis or had oligometastatic recurrences during follow-up. All patients were treated with the goal of curing their metastasis, and 839 lesions were irradiated. The average age was 61 years (range; 27-92 years). The majority of patients (58.8%) had colon carcinoma with a single organ metastasis (88.8 %). The average number of metastatic lesions was 2 (range, 1-5). There were 103 patients with liver metastasis, 222 patients with lung metastasis, 58 patients with lymph node metastasis, 60 patients with bone metastasis, 32 patients with brain metastasis, and 6 patients with other organ metastasis. Before RT, the median CEA and Ca-19-9 levels were 5.16 ng/mL (range: 0-8181.1 ng/mL) and 19.4 (range: 0.60 - 3693), respectively. After RT, the median CEA and Ca-19-9 were 5.00 ng/mL (range, 0.4-5693v ng/mL) and 18 (range, 0 - 6577), respectively. The average period of follow-up was 15.2 months (range, 0.3-91.5 months). The rates of OS and PFS after two years were 76.3 % and 28.1 %, respectively. Age (p<0.001), pre-RT CEA (p=0.006), pre-RT Ca19-9 (p=0.02), post-RT CEA (p=0.01), and post-RT Ca19-9 (p=0.02) were all significant prognostic factors for OS in univariate analysis. Age (HR=1.03, 95 % CI, 1.01-1.04, p=0.004) and pre-RT CEA (HR=1.01, 95 % CI, 1.00-1.02, p=0.04) were independent predictors of OS in multivariate analysis, while post-RT CEA (HR=1.93, 95 % CI, 1.28-2.90, p=0.002) was an independent predictor of PFS. SBRT to oligometastatic lesions was found to be a safe and effective treatment modality for patients with colorectal cancer. Survival was predicted by age, baseline CEA, and the Ca19-9 response to MDT. Additional prospective studies with larger cohorts are necessary to validate our findings. [ABSTRACT FROM AUTHOR]

Radiotherapy has an important role in management of lung tumors. Online adaptive radiotherapy is a method that provides dosimetric accuracy by considering anatomical and functional changes with real-time images taken during treatment, and MR-guided radiotherapy is the latest technological development in this field. In our study, we aimed to present preliminary results and toxicity in patients who underwent magnetic resonance (MR) guided online adaptive radiotherapy (MRgRT) for primary or metastatic lung tumors. Fifty-one patients with a diagnosis of primary lung cancer or lung metastases treated with MRgRT and a minimum follow-up period of 3 months were included. The treatment was carried out with the "step-and-shoot" IMRT technique and daily online adaptive planning. All patients were treated with breath-hold with audio-visual coaching. Patients were evaluated for treatment response, acute and late toxicity. The median age was 64 (range, 22-83 years) and 68.6% of the patients were male. MRgRT was performed in 21.6% of the patients for primary lung cancer and 78.4% for lung metastases from different primaries. MRgRT was applied to a single lesion in 38 patients and more than one lesion in 13 patients (a total of 69 lesions). Tumors were peripherally located in 78.3% of the patients and 21.7% of lesions were in the "no-fly zone". Median GTV volume was 1.8 cc (range, 0.2-172.1 cc). Target volume and doses of organs at risk met the criteria in all initial plans. Online adaptive treatment approach was applied in all patients. The median total dose was 50 Gy (range, 24-70), the median fraction number was 5 (range, 1-15 fractions), and the median fraction dose was 10 Gy (range, 4-34). The patients were treated every other day, except for two patients treated with 10 and 15 fractions. Median follow-up was 18.7 months. One- and 3-year overall survival (OS) rates were 92.4% and 68.0%, respectively. During the follow-up period, complete response was obtained in the MRgRT applied lesions in 37 patients, partial response was observed in 8 patients and local recurrence or progression was detected in 6 patients. One- and 3- year local progression free survival (LPFS) and distant progression free survival (DPFS) rates were 97.3%, 67.1% and 36.4%, 13.0%, respectively. There were no statistically significant differences in OS, LPFS and DPFS between primary and metastatic tumors. No Grade 3+ acute or late toxicity was observed. In conclusion, MRgRT is a new method for the application of SBRT with better soft tissue contrast, no need for invasive marker placement, online adaptive radiotherapy in every fraction, and continuous real-time cine-MR tumor tracking. Our study shows that MRgRT is an acceptable method for the treatment of lung tumors. Randomized prospective studies with longer follow-up are needed comparing this technique with other modalities. [ABSTRACT FROM AUTHOR]