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Partial tumor irradiation (PTI) is a novel immunomodulatory concept which adds to the direct cell-killing radiation effects an additional component of immune-mediated tumor cell-killing. PTI consists of 3 key principles: (1) neutralizing the immunosuppressive, central hypovascularized, and hypometabolic tumor segment, (2) preserving the peritumoral immune microenvironment (PIM) as OAR, and (3) delivering the treatment at precisely planned times, individually tailored for each patient based on homeostatic oscillations of immune activity (time-synchronized immune-guided radiotherapy). We hypothesized that PTI would generate radio-immunogenic effects thereby enhancing patient prognosis. The primary endpoint: bystander and abscopal responses rate. This is a mono-centric, prospective, two-arm, phase 1 proof of principle trial including 22 patients with complex unresectable bulky tumors and at least 1 untreated metastatic site, deemed unsuitable for standard radiotherapy experiencing disease progression despite systemic therapies. Hypovascularized and hypometabolic tumor segment, delineated using the c.e. CT and FDG-PET-CT, was targeted with 10 Gy x 3 at 70% sparing the PIM. 2 weeks prior PTI, each patient had 7 serial blood draws assessing CRP, LDH and lymphocyte/monocyte ratio to determine each patient´s idiosyncratic immune activity cycle. First 11 patients (arm 1) PTI was delivered at an estimated "less reactive day" and to last 11 patients (arm 2) at "most reactive day." In selected patients, residual tumors, radiation-spared PIM and unirradiated abscopal tumor sites were surgically removed for immunohistochemistry (IHC) and cell-death inducing genes (CDIG) analysis. PTI exhibited significant radio-immunogenic effect (Tab. 1). Arm 2 demonstrated superior outcomes across nearly all treatment aspects. A higher proportion of long-term survivors were from arm 2 (55%, median follow-up of 54 months) compared to arm 1 (27%, median follow-up of 43 months). IHC and CDIG revealed significant anti-tumor-directed-activation of the immune system. PTI was safe and effective. This study highlights the profound impact PTI can have on a highly palliative patient cohort previously deemed beyond therapeutic hope. It revealed the critical impact of treatment timing on clinical outcomes which has significant implications for optimizing individualized cancer treatment. [ABSTRACT FROM AUTHOR]

Protons and carbon ions each confer dosimetric advantages over photons, yet of these modalities, only carbon ion radiotherapy (CIRT) delivers densely ionizing, high linear energy transfer (LET) radiation which results in more complex DNA damage and an increased relative biological effectiveness (RBE) compared to low LET photons. However, our classical understanding of RBE does not account for potential microenvironmental effects. We therefore performed a multi-institutional, multi-omics analysis to understand how CIRT shifts the contexture of the tumor immune microenvironment in pancreatic cancer. Murine pancreatic cancer cell lines derived from KrasLSL-G12D/+; Trp53LSL-R172H/+; Pdx1-CreERTM; Rosa26YFP/YFP (KPCY) mice which exhibit low T-cell infiltration (6419c5) vs. high T-cell infiltration (2838c3) were studied. These tumor cell lines were implanted subcutaneously into wild-type (WT) C57BL/6J or immunodeficient NSG mice and irradiated 7 days later. CIRT was performed at an LET d of ∼100 keV/μm in the mid-spread-out Bragg peak (SOBP) while low LET photon treatments were performed using orthovoltage X-rays or 137Cs γ-rays. Clonogenic assays were performed to determine the RBE, and proteomics was performed by mass spectrometry on cell culture supernatant 24 hours post-radiation. 6419c5 flank tumors were dissociated 7 days post-10 Gy of CIRT or X-rays and single cell RNA-sequencing (scRNA-seq) was performed on sorted live cells. Clonogenic assays in both cell lines revealed a CIRT RBE of 1.76 compared to photons. Despite these cell lines exhibiting similar clonogenic survival after CIRT in vitro, the response to CIRT in vivo was notably different between them in tumor growth experiments. There was a similar tumor growth delay with 10 Gy CIRT in both WT and NSG mice with 6419c5 tumors. However, 2838c3 responded to 10 Gy CIRT with a significantly longer tumor growth delay in WT vs. NSG mice (P < 0.05), suggesting that tumor infiltrating T lymphocytes contribute to tumor control after CIRT. Overlap analysis of common differentially expressed proteins related to CIRT from both cell lines identified a unique signature of CIRT with 25 upregulated and 5 downregulated proteins. scRNA-seq identified that CIRT upregulates genes and pathways associated with the response to type I interferons and with antigen presentation across populations including tumor cells, dendritic cells, and T/NK cells 7 days post-irradiation when compared to an equivalent physical dose of X-rays. CIRT not only exhibited an increased RBE, but it also generated a unique tumor immune microenvironment characterized by transcriptional evidence of a type I interferon response and enhanced antigen presentation when compared to low LET radiation. Tumor growth experiments further suggest that effective immune activation could contribute to the augmented in vivo RBE of CIRT. [ABSTRACT FROM AUTHOR]

Initial reports from the S elective P ersonalized R adioimmunotherapy for Locally Advanced N SCLC T rial (SPRINT) indicated that patients with high PD-L1 expression can be treated safely and effectively with immunotherapy and radiotherapy (RT). Here, we compare patient-reported outcomes (PROs) from SPRINT to PROs from patients who were treated with standard concurrent chemoradiotherapy on contemporary prospective trials to test the hypothesis that the SPRINT approach yields favorable patient-reported outcomes. SPRINT participants with PD-L1 tumor proportion score ≥ 50% were treated with "PembroRT": three 21-day cycles of induction pembrolizumab, a four-week course of risk-adapted and de-intensified RT (55 Gy to tumors or lymph nodes measuring 20 cc or larger and 48 Gy to smaller lesions, all in 20 fractions and without concurrent chemotherapy), and up to 13 cycles of consolidation pembrolizumab. SPRINT participants with lower PD-L1 expression and participants on the control arm of NCT03481114 were treated with "ChemoRT": a standard RT dose of 60 Gy in 30 fractions with concurrent weekly carboplatin and paclitaxel and standard adjuvant therapy (e.g., durvalumab). Participants in both trials completed a 12-item PRO-CTCAE survey at baseline, every two weeks during RT, and at follow-up visits. Study participants who completed the planned RT course and completed at least two PRO-CTCAE surveys were included in this analysis. Peak PRO-CTCAE grades recorded up to 90 days after RT completion were compared across treatment cohorts using Kruskal-Wallis testing. Multivariable logistic regression models were utilized to evaluate predictors of grade 2+ patient-reported toxicity. Kaplan-Meier curves and log rank testing were utilized to compare progression-free survival (PFS) and overall survival (OS) across treatment cohorts. The PembroRT cohort included 19 patients, and the ChemoRT cohort included 26 patients. Mean esophagus and lung doses were significantly lower in the PembroRT cohort, with median values approximately 5 Gy lower than in the ChemoRT group. Average PRO-CTCAE grades were numerically higher in the ChemoRT group for all 12 symptoms, with statistically significant differences observed for cough, wheezing, dermatitis, dizziness, anxiety, and depression. Multivariable models demonstrated that patient-reported toxicity was generally not associated with chemotherapy receipt, while several patient-reported adverse events were associated with organ at risk doses. For example, grade 2+ dysphagia incidence was associated with mean esophageal dose. The PembroRT cohort had superior 3-year rates of PFS (61% v. 23%, P = 0.033) and OS (88% v. 49%, P = 0.013). Compared to standard chemoradiotherapy, the SPRINT treatment approach, which utilizes induction immunotherapy to reduce target volumes and risk-adapted RT, can improve patient-reported outcomes without compromising clinical outcomes. [ABSTRACT FROM AUTHOR]

Radiation therapy is traditionally used for the local control of tumour growth, but recent studies suggest that radiation therapy can have immunomodulatory properties that can be applied in combination therapy with immunotherapeutic agents. The paradigm of using radiation therapy for immunomodulation in cancer treatment is a rapidly progressing field, with multiple ongoing clinical trials exploring its use in combination with immune checkpoint blockades to induce an abscopal effect. Permutations of radiation therapy regimens, including variations in radiation dosing, radiation planning parameters and radiation modality, are being tested with varying degrees of success. The relative biological effectiveness was a concept introduced in the early days of radiation biology that allows the comparison of local tumour control across various radiation modalities and energies. Similarly, there remains a need for a new concept of comparing the immunological effectiveness of various radiation modalities. In this review, we will provide an overview of immunobiological models for preclinical and clinical monitoring of radiation therapy regimens and introduce the concept of relative immunological effectiveness to compare and screen for immune-activating functions of these regimens. [ABSTRACT FROM AUTHOR]

Despite association between distress and worsened overall survival, little is known about specific causes of distress. The primary objective of this study was to identify stressors in patients with cancer receiving curative intent radiation therapy (RT) at a racially/ethnically diverse urban academic center. A secondary objective sought to evaluate the coping mechanisms used by these patients. This prospective, IRB approved, single institution, mixed methods study enrolled a pre-planned sample of 40 patients between 4/2021 and 2/2022. Distress was measured via the NCCN recommended Distress Thermometer (DT); specific stressors were determined using the Cancer Treatment and Distress Scale (CTDX) and coping methods using the Brief Cope (BC). All three questionnaires were completed prior to starting RT. Post-RT questionnaires and interview data is not yet mature and will not be reported here. DT was evaluated as both a continuous and dichotomized variable with a score of≥4 being distressed. Chi-squared, Wilcoxon rank-sum, and Pearson correlation tests were used, as appropriate, to assess these relationships. 39 patients completed study questionnaires. Patients predominantly self-identified as female (62%) and a minority (39% African American, 37% Hispanic). Of the 23 patients who reported their income, 52% had an annual income ≤$40,000. Most cancers were early stage (47% stage I-II) with the most common cancer types of breast (31%), prostate (23%), and gynecological (18%). 76% of patients reported feeling distressed (median 6, IQR 4-8). The strongest correlations between the DT and the CTXD, were related to health burden (physical limitations due to disease and treatment) (r=0.64, p<0.001) and uncertainty about the future/disease course (r=0.61, p<0.001). When evaluating coping strategies, higher DT scores (r=0.40, p=0.030) were associated with increased likelihood of using avoidant coping styles such as self-distraction, denial, and substance use. There was no association between feeling distressed and gender, race/ethnicity, income, receiving surgery or chemotherapy prior to RT, nor receiving concurrent chemoradiation. We found >75% endorsed clinical levels of distress, which is much higher than the ≤50% seen in predominantly white populations. These results suggest there is an opportunity to dramatically reduce distress in these economically disadvantaged cancer patients. Potential approaches for distress reduction could include targeted interventions such as pre-emptive rehabilitation medicine to improve physical function, an iterated education program based on patient understanding to ameliorate uncertainty, and mindfulness therapy to develop effective coping strategies. [ABSTRACT FROM AUTHOR]

This study investigates the association between pre-treatment positron emission tomography (PET) metrics and clinical outcomes in anal squamous cell carcinoma (ASCC) patients treated with definitive radiation therapy (RT). We hypothesize that pre-treatment PET metrics may differentially predict clinical outcomes in ASCC patients without HIV infection (HIV-) and ASCC patients living with HIV (PLWH) with detectable or undetectable viral load (VL). Patients treated with definitive RT for non-metastatic ASCC between 2005 - 2021 at a single institution were retrospectively identified, and clinical and demographic data, including HIV status and pretreatment VL, were tabulated. Pre-treatment PETs were imported to MIM, and semiautomatic gradient-based segmentation tool algorithms (PET_Edge) were used to calculate PET metrics, including maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG). Cox proportional hazard modeling was used to investigate the association between primary tumor PET metrics and clinical outcomes, including overall survival (OS), progression free survival (PFS), and loco-regional control (LRC) 141 ASCC patients were identified, 49 of whom were PLWH. 12 had detectable HIV VL. The median follow-up time was 51.8 months (IQR: 0.5-191.2 months). There were 22 loco-regional failures and 24 deaths. 3- and 5- year LRC was 85.6% and 83.3%, 3- and 5- year PFS was 75.9% and 71.6%, and 3- and 5- year OS was 89.3% and 86.6% for the entire cohort. There was no significant difference in LRC, PFS, or OS between PLWH and HIV- patients (p>0.50). PLWH with detectable VL had similar LRC and PFS but trended towards worse 5-year OS than did HIV- patients (66.3% vs 89.7%, p=0.16). MTV and TLG from primary tumors were significantly associated with LRC, PFS, and OS for all patients and in sub-group analysis for HIV-, PLWH, and PLWH with undetectable VL (p<0.05). SUVmax was significantly associated with LRC, PFS, and OS for all patients, and on sub-group analysis only for HIV- patients (p<0.05). On multivariable analysis, after adjusting for stage and Charlson Comorbidity Index, MTV split at median was significantly associated with LRC (HR 3.59 (95% CI:1.21-10.6), p=0.02) and PFS (HR 3.12 (95%CI:1.48-6.56), p=0.003), and TLG split at median was significantly associated with LRC (HR 4.36 (95%CI:1.36-14.0), p=0.01) and PFS (HR 3.13 (95%CI:1.48-6.64), p=0.003). Patients with ASCC had similar outcomes regardless of HIV status. Advanced pre-treatment PET metrics, especially MTV and TLG, may have prognostic or risk-stratification utility in HIV- patients and undetectable PLWH with ASCC, but were not as strongly associated with clinical outcomes for PLWH with detectable VL, perhaps due to small numbers of patients with detectable VL in this cohort. [ABSTRACT FROM AUTHOR]

To quantify imaging changes from pre- to post-treatment dynamic contrast enhanced (DCE) MRI following liver SBRT for hepatocellular carcinoma (HCC) and examine the association with changes in albumin-bilirubin (ALBI) score. Patients from a single institution treated with liver SBRT for HCC with available DCE-MRIs using a hepatocyte-specific contrast agent, Gb-EOB-DTPA, were identified. Whole liver volumetric contours were delineated on all dynamic MRI phases for pre- and post-treatment scans. Post-treatment scans were registered to the pre-treatment scans using rigid registration (median DICE coefficient 0.88, range: 0.75 to 0.95). A 3-compartment kinetic model was used to fit the signal intensity data over time from the DCE-MRI scans using the abdominal aorta as vascular input function surrogate. The area under the modeled signal intensity curve from zero to 20 minutes post contrast injection (AUC 20) was estimated for each individual liver voxel (∼12,000 voxels when downsampled to ∼4 × 4 × 6 mm3) and was used as an indicator of imaging-based liver function. ALBI scores were calculated from each patient's medical records at pre-treatment and at 6 months post SBRT. The association between change in AUC 20 throughout any part of the liver and change in ALBI score was assessed using linear regression and t-test. Thirty-six patients met inclusion criteria. All patients were treated in five fractions with the majority treated to a total dose of 50 Gy (70%). The median time from SBRT to analyzed post-treatment MRI scan was 6 months (range: 4-8 months). Median baseline ALBI score was -2.49 (range: -3.29 to -1.35) and the median change in ALBI score was 0.17. The average pre-treatment AUC 20 within all liver voxels was 3.38 (±1.36), compared to 3.09 (±1.39) at post-treatment. For most patients there was not a considerable change in median AUC 20 , but for the patients with >30% reduction in AUC 20 the average worsening in ALBI score was 0.45 points. The change in AUC 20 was significantly correlated with the change in ALBI score at 6 months (p=0.012). Linear regression analysis adjusted for baseline ALBI score showed a significant worsening of ALBI score with increasing reduction in median AUC 20 (p=0.017). Patients with clinically significant worsening of ALBI score at 6 months (at least 0.5-point increase) had an average 33% reduction in median AUC 20 compared to an average 2% increase in AUC 20 for patients without clinically significant ALBI score change (p=0.014). Post-treatment changes in MR-based liver imaging assessed by reduction in AUC 20 were significantly associated with change in ALBI score. This type of voxel-wise estimation of region-specific imaging features could potentially be used to improve future treatment personalization. [ABSTRACT FROM AUTHOR]

The role of SBRT in the treatment of HCC is not well established. The hypothesis of this study was that overall survival (OS) would improve with SBRT followed by sorafenib (SBRT/S) vs. sorafenib alone (S), in patients with advanced HCC. Eligible patients had new or recurrent HCC, unsuitable for resection, transplant, ablation or TACE, with Zubrod performance status (PS) 0-2, Child-Pugh A, intermediate (B) or advanced (C) Barcelona Clinic Liver Cancer Stage (BCLC), ≤ 5 HCCs, sum of hepatic HCCs ≤ 20 cm, and sum of extrahepatic metastases ≤ 3 cm. Patients were randomized 1:1 to S 400 mg BID vs. SBRT (27.5-50Gy in 5 fractions, with dose individualized based on mean liver dose and other dose constraints) followed by S 200 mg BID then increased to 400 mg BID after 28 days if appropriate. Primary endpoint was OS. Reported secondary endpoints were progression-free survival (PFS), time to progression (TTP), and adverse events (AEs - CTCAEv4). Planned sample size was 292 patients (238 OS events, HR=0.72, 80% power, 1-sided alpha=0.05). Accrual closed early, primarily due to a change in HCC standard of care systemic therapy. Statistics were amended to report data as of 7/1/2022, projecting 155 OS events providing 65% power for the original hypothesis, with the same alpha. OS and PFS were estimated by Kaplan-Meier and arms compared using log-rank test. Cox proportional hazards models were used to analyze treatment effect. TTP was estimated with cumulative incidence and arms compared using Gray's test. Secondary endpoints were tested with 2-sided alpha=0.05. Of 193 patients accrued from April 2013 to March 2021 from 23 sites, 177 eligible patients were randomized to S (n=92) vs. SBRT/S (n=85). Median age was 66 years (27-84); 41% had Hepatitis C and 19% had Hepatitis B or B/C. The majority were stage BCLC C (82%), with macrovascular invasion (74%). 4% had metastases. Median follow-up for all and alive patients was 13.2 and 33.7 months, respectively. With 153 OS events, median OS was improved from 12.3 months (90% CI 10.6, 14.3) with S to 15.8 months (90% CI 11.4-19.2) with SBRT/S (HR=0.77, 1-sided p=0.0554). After adjusting for PS, M stage, Child Pugh A5 vs. 6, and degree of vascular HCC, OS was statistically significantly improved for SBRT/S (HR=0.72, 95% CI 0.52-0.99, 2-sided Cox p=0.042). Median PFS was improved from 5.5 months (95% CI 3.4-6.3) with S to 9.2 months (95% CI 7.5-11.9) with SBRT/S (HR=0.55, 95% CI 0.40-0.75, 2-sided p=0.0001). TTP was also improved with SBRT/S (HR=0.69, 95% CI 0.48-0.998, 2-sided Gray's p=0.034). Treatment-related grade 3+ AEs were not significantly different (S - 42%, SBRT/S - 47%; p=0.52). There was one grade 5 treatment-related AE, in the S arm. Adding SBRT improved OS, PFS, and TTP in patients with advanced HCC, compared to Sorafenib alone, with no significant increase in AEs. [ABSTRACT FROM AUTHOR]

The use of stereotactic body radiation therapy (SBRT) for hepatocellular carcinoma (HCC) has been steadily increasing. Recently, it was reported that patients with HCC have a differential response to immune-checkpoint inhibitor based on the background liver disease etiology. Whether outcomes of SBRT are affected by underlying liver disease etiology is currently unknown. We therefore reviewed outcomes of SBRT with special focus on tumor size, BED, and underlying liver disease etiology. This study is a retrospective review of HCC patients treated with SBRT at one institution between 2009 and 2021. Patients with tumor thrombus or extrahepatic disease were excluded. Kaplan-Meier curves and Cox regression models were used to describe freedom from local progression (FFLP) and overall survival (OS) rates and examine potential prognostic factors. One-hundred and sixty-four patients met study entry criteria. Median gross tumor volume (GTV) size was 9.3 cc (range 0.3 to 762.4 cc). 67% of patients had a history of hepatitis C, and 9% had a history of hepatitis B. 71% of patients received our institutional standard SBRT dose of 50 Gy in 5 fractions (biological effective dose [BED] 100 Gy). Other patients received lower doses ranging from 30 to 47.5 Gy in three to five fractions (BED range 48 to 93 Gy) if necessary to preserve normal liver tissue. Median follow-up time was 43 months (interquartile range [IQR] 36 to 52 months). Seventeen in-field failures and 67 deaths have occurred. 3- and 5-year FFLP rates were 84% and 75%, and 3- and 5-year OS rates were 65% and 48%, respectively. History of hepatitis C was associated with better FFLP (HR=0.36 (95% CI:0.14, 0.94), p=0.038). Treatment with 50 Gy was associated with better FFLP compared to treatment with lower doses for patients with hepatitis C (HR=0.15 (95%CI: 0.04, 0.63), p=0.01) but not for other patients (HR=3.1 (95%CI: 0.38, 24.7), p=0.29). SBRT for HCC yields excellent local control, particularly for patients with hepatitis C. In hepatitis C patients, dose escalation beyond a BED of 100Gy may be more important for local control than in non-hepatitis C patients. More studies are necessary to better understand if HCC etiology should be considered when planning SBRT. [ABSTRACT FROM AUTHOR]

Liver-directed therapy (LDT) following transarterial chemoembolization (TACE) can lead to improvement in survival for selected patients with unresectable hepatocellular carcinoma (HCC). However, there is uncertainty in the appropriate application and modality of therapy in current clinical practice guidelines. The aim of this study was to develop a proof-of-concept, machine-learning (ML) tool for treatment recommendation in patients previously treated with TACE and identify patients who may benefit from additional treatment with combination stereotactic body radiotherapy (SBRT) or radiofrequency ablation (RFA). This retrospective, observational study was based on data from an urban, academic hospital system selecting for patients diagnosed with stage I-III HCC from January 1, 2008 to December 31, 2018, treated with TACE, followed by adjuvant RFA, SBRT, or no additional liver-directed modality. The dataset was divided in half into training and testing groups. A feed-forward ML ensemble model based on the DeepSurv algorithm, provided a treatment recommendation using pair-wise assessments between each potential treatment option and an estimated benefit in survival. Final ensemble model treatment recommendation was selected based on the treatment yielding the best hazard rate among all pairwise models on an individual patient basis. Two hundred thirty-seven patients met inclusion criteria, of whom 54 (23%) and 49 (21%) received combination TACE and SBRT or TACE and RFA respectively. The ML model recommended a different consolidative modality in 33% of cases among patients who had previously received combination treatment. Patients treated in concordance with model recommendations had a numerical improvement in overall survival (HR 0.63; p=0.160) and significant improvement in progression free survival (HR 0.50; p=0.007). The most critical features for model treatment recommendation were cause of cirrhosis, stage of cancer, and ALBI grade (a measure of liver function). In this proof-of-concept study, we developed an ensemble ML model which was able to provide treatment recommendations for HCC who had undergone prior TACE therapy. Our data suggest additional treatment in-line with model recommendations was associated with significant improvement in progression free survival suggesting a potential benefit for ML-guided medical decision making. In the future, this tool will provide the framework for a prospective study where treatment decisions for complex clinical cases may be enhanced through personalized, machine-learning recommendations. [ABSTRACT FROM AUTHOR]

Metastatic epidural spinal cord compression (MESCC) can be very painful and disabling. We hypothesized that an initial fraction of SBRT would provide rapid decompression and allow for potential dose escalation via a follow up treatment. Our primary objective was to assess the feasibility of a staged SBRT approach to provide short-interval treatment response. Secondary endpoints included pain control and quality of life (QoL). This single institution, prospective study enrolled non-surgical candidates with MESCC from 07/2015 to 02/2018. Those with spine instability (SINS>12), bony retropulsion, or radiosensitive histologies were excluded. After baseline imaging (MRIpre), patients received SBRT (10-16 Gy) and a short interval MRI within 2-3 weeks (MRI1). Subsequently, patients could receive an additional treatment at the discretion of the treating physician. A second MRI was completed 8-10 weeks post-tx (MRI2). QoL questionnaires and pain scores were obtained at all time points. The primary endpoint was the smallest cord-disease distance (CDD) in the axial plane and the thecal sac patency (TSP), defined as the thecal sac area at the level of maximal compression divided by the average thecal sac area one level above and below. Secondary endpoints included pain scores and QoL using the Functional Assessment of Cancer Therapy – General (FACT-G). Statistical comparisons utilized the Wilcoxson signed-rank test. 22 patients were enrolled in the study and received SBRT. The most common primary diagnoses were lung (36%) and prostate (32%) cancer. The most common initial SBRT doses were 16 Gy (41%) and 14 Gy (36%). 12 patients completed all 3 scans and 3 other patients completed 2 scans (MRIpre and either MRI1 or MRI2). No patient received a second,adaptive fraction of radiation (due to lost to follow up, systemic progression, or no local progression). TSP significantly increased on MRI1 (median change 9%, IQR 1%-28%, p = 0.034) and on MRI2 (median change 24%, IQR 12-32%, p = 0.002). CDD did not increase significantly on MR1 (median change 0.0 mm, IQR 0-0.3 mm, p = 0.125) but did on MRI2 (median change 1.5 mm, IQR 0-1.8 mm, p = 0.001). On radiology report, 23% had disease improvement on MRI1, all of whom received 16 Gy. 64% had disease improvement on MRI2. No patients progressed neurologically. There was a numerical decrease in best and worst pain score over time (p=0.093). FACT-G scores did not change significantly over time. There were no grade 3 or greater toxicities related to RT. Single-fraction SBRT can provide rapid decompression of epidural disease safely and quickly. Radiosurgical decompression can be a feasible alternative to surgery in patients with MESCC, especially as a large segment of such patients are non-surgical candidates. A follow up study comparing SBRT to 3D CRT is being planned. [ABSTRACT FROM AUTHOR]