Three-dimensional printing in radiation oncology: A systematic review of the literature

Purpose/objectives

Three‐dimensional (3D) printing is recognized as an effective clinical and educational tool in procedurally intensive specialties. However, it has a nascent role in radiation oncology. The goal of this investigation is to clarify the extent to which 3D printing applications are currently being used in radiation oncology through a systematic review of the literature.

Materials/methods

A search protocol was defined according to preferred reporting items for systematic reviews and meta‐analyses (PRISMA) guidelines. Included articles were evaluated using parameters of interest including: year and country of publication, experimental design, sample size for clinical studies, radiation oncology topic, reported outcomes, and implementation barriers or safety concerns.

Results

One hundred and three publications from 2012 to 2019 met inclusion criteria. The most commonly described 3D printing applications included quality assurance phantoms (26%), brachytherapy applicators (20%), bolus (17%), preclinical animal irradiation (10%), compensators (7%), and immobilization devices (5%). Most studies were preclinical feasibility studies (63%), with few clinical investigations such as case reports or series (13%) or cohort studies (11%). The most common applications evaluated within clinical settings included brachytherapy applicators (44%) and bolus (28%). Sample sizes for clinical investigations were small (median 10, range 1–42). A minority of articles described basic or translational research (11%) and workflow or cost evaluation studies (3%). The number of articles increased over time (P < 0.0001). While outcomes were heterogeneous, most studies reported successful implementation of accurate and cost‐effective 3D printing methods.

Conclusions

Three‐dimensional printing is rapidly growing in radiation oncology and has been implemented effectively in a diverse array of applications. Although the number of 3D printing publications has steadily risen, the majority of current reports are preclinical in nature and the few clinical studies that do exist report on small sample sizes. Further dissemination of ongoing investigations describing the clinical application of developed 3D printing technologies in larger cohorts is warranted.

Bringing high-grade arteriovenous malformations under control: clinical outcomes following multimodality treatment in children

OBJECTIVE

Brain arteriovenous malformations (AVMs) consist of dysplastic blood vessels with direct arteriovenous shunts that can hemorrhage spontaneously. In children, a higher lifetime hemorrhage risk must be balanced with treatment-related morbidity. The authors describe a collaborative, multimodal strategy resulting in effective and safe treatment of pediatric AVMs.

METHODS

A retrospective analysis of a prospectively maintained database was performed in children with treated and nontreated pediatric AVMs at the University of California, San Francisco, from 1998 to 2017. Inclusion criteria were age ≤ 18 years at time of diagnosis and an AVM confirmed by a catheter angiogram.

RESULTS

The authors evaluated 189 pediatric patients with AVMs over the study period, including 119 ruptured (63%) and 70 unruptured (37%) AVMs. The mean age at diagnosis was 11.6 ± 4.3 years. With respect to Spetzler-Martin (SM) grade, there were 38 (20.1%) grade I, 40 (21.2%) grade II, 62 (32.8%) grade III, 40 (21.2%) grade IV, and 9 (4.8%) grade V lesions. Six patients were managed conservatively, and 183 patients underwent treatment, including 120 resections, 82 stereotactic radiosurgery (SRS), and 37 endovascular embolizations. Forty-four of 49 (89.8%) high-grade AVMs (SM grade IV or V) were treated. Multiple treatment modalities were used in 29.5% of low-grade and 27.3% of high-grade AVMs. Complete angiographic obliteration was obtained in 73.4% of low-grade lesions (SM grade I-III) and in 45.2% of high-grade lesions. A periprocedural stroke occurred in a single patient (0.5%), and there was 1 treatment-related death. The mean clinical follow-up for the cohort was 4.1 ± 4.6 years, and 96.6% and 84.3% of patients neurologically improved or remained unchanged in the ruptured and unruptured AVM groups following treatment, respectively. There were 16 bleeding events following initiation of AVM treatment (annual rate: 0.02 events per person-year).

CONCLUSIONS

Coordinated multidisciplinary evaluation and individualized planning can result in safe and effective treatment of children with AVMs. In particular, it is possible to treat the majority of high-grade AVMs with an acceptable safety profile. Judicious use of multimodality therapy should be limited to appropriately selected patients after thorough team-based discussions to avoid additive morbidity. Future multicenter studies are required to better design predictive models to aid with patient selection for multimodal pediatric care, especially with high-grade AVMs.

High-Flow Vascular Malformations in Children

Children can have a variety of intracranial vascular anomalies ranging from small and incidental with no clinical consequences to complex lesions that can cause substantial neurologic deficits, heart failure, or profoundly affect development. In contrast to high-flow lesions with direct arterial-to-venous shunts, low-flow lesions such as cavernous malformations are associated with a lower likelihood of substantial hemorrhage, and a more benign course. Management of vascular anomalies in children has to incorporate an understanding of how treatment strategies may affect the normal development of the central nervous system. In this review, we discuss the etiologies, epidemiology, natural history, and genetic risk factors of three high-flow vascular malformations seen in children: brain arteriovenous malformations, intracranial dural arteriovenous fistulas, and vein of Galen malformations.

MNGI-04. PATTERNS OF FAILURE AND FACTORS INFLUENCING LOCAL RECURRENCE OF MENINGIOMA TREATED WITH POSTOPERATIVE RADIATION THERAPY

BACKGROUND

Factors associated with meningioma recurrence after postoperative radiotherapy are poorly understood, and the optimal postoperative radiotherapy target delineation for meningioma is unknown. The objective of this study was to identify factors influencing meningioma recurrence after postoperative radiotherapy to inform patient selection and treatment design.

METHODS

Medical records were retrospectively reviewed for patients who underwent meningioma resection at a single institution between 1991 and 2015. Patients with sufficient tumor tissue for histologic classification and who received postoperative radiation therapy with external beam radiotherapy (EBRT), stereotactic radiosurgery (SRS) or brachytherapy, were included. Local freedom from recurrence (LFFR) was analyzed according to tumor and treatment characteristics using the Kaplan Meier method.

RESULTS

We identified 86 patients with 96 meningiomas who met inclusion criteria. Nineteen meningiomas (20%) were WHO grade I, 56 (58%) were grade II and 21 (22%) were grade III. Forty-one meningiomas (43%) were recurrent, and 55 (57%) were de novo. The postoperative radiotherapy modality was EBRT for 58 patients (60%), SRS for 20 (21%) patients and brachytherapy for 18 (19%) patients. With a median follow up of 4.3 years (IQR 2.1–8.8 years), there were 48 (50%) local failures that occurred a median of 17 months after immediate prior resection (IQR 9–33 months). WHO grade II/III and recurrent meningiomas had worse LFFR (p< 0.001). The 5-year LFFR was 53% after EBRT (95% CI 41–69%), 53% after SRS (95% CI 34–84%) and 15% after brachytherapy (95% CI 3–74%), although meningiomas that were treated with brachytherapy were significantly more likely to have received prior EBRT or SRS (86% versus 29%, p< 0.001).

CONCLUSIONS

These data provide a foundation for understanding patterns of meningioma recurrence after postoperative radiotherapy. Ongoing analyses aim to quantify the relationships between postoperative radiotherapy dose, target delineation and local control of meningioma.

GENE-37. VESTIBULAR SCHWANNOMA IS COMPRISED OF NEURAL CREST AND IMMUNE SUBGROUPS

BACKGROUND

Vestibular schwannomas (VS) are tumors arising from cranial nerve Schwann cells and show variable outcomes after treatment, including oscillation in size for many years after radiosurgery. To understand the unique biology of VS, we performed multiplatform molecular profiling to develop a single cell atlas of VS and reveal that VS exists on a molecular axis defined by neural crest and immune genes.

METHODS

Sixty-six sporadic VS with available tissue for molecular profiling from 59 consecutive patients at a single institution were included. 850K DNA methylation arrays and RNA sequencing were used to profile both primary (76%) and recurrent (24%) tumors. Single nuclei RNA sequencing of 7 tumors and single cell RNA sequencing of 3 tumors and cell lines were used to define the cellular composition of VS and heterogeneous changes in molecular programs following irradiation. Molecular subtyping was performed by hierarchical clustering of differentially-methylated DNA probes and validated using transcriptomic data. Mechanistic experiments were performed using cultured human schwann cells and human vestibular schwannoma cells, confocal microscopy, CRISPR interference, proteomic mass spectrometry and lymphocyte migration assays.

RESULTS

Multiplatform genomic profiling and machine learning revealed that VS is comprised of two distinct molecular subtypes characterized by heterogeneous cell populations. Neural crest enriched VS express primary cilia and are associated with misactivation of the Hedgehog pathway. Consistently, we find that the Hedgehog pathway antagonist vismodegib blocks the growth of human Schwann cells. Irradiation epigenetically reprograms tumors and cell lines to reduce ciliary length, attenuate Hedgehog signaling, activate senescence pathways, and express cytokines and apolipoproteins that recruit lymphocytes and macrophages to immune enriched VS.

CONCLUSIONS

Our data reveal novel molecular subtypes of VS and establish a framework for understanding how irradiation modifies the epigenome and tumor microenvironment.

HOUT-07. ASSOCIATION BETWEEN BASELINE BODY MASS INDEX (BMI) AND OUTCOMES FOR PATIENTS WITH GLIOBLASTOMA

OBJECTIVES

This single institution retrospective study aims to evaluate the association between body mass index (BMI) and survival in glioblastoma (GBM).

METHODS

Patients were identified using a single institution cancer registry. Baseline height and weight were obtained at first clinical visit after diagnosis. Inclusion criteria were GBM diagnosis after 1999 with available height and weight data. Follow up was through July 2018.

RESULTS

779 patients were included who had available BMI data. Median age was 58 (IQR 48–66). 38% of patients were female and 62% were male. Median overall survival (OS) was 1.34 years (IQR 0.78–2.12) and median BMI was 26.01 (IQR 23.3–29.1). There was no strong linear correlation between OS and BMI using Pearson correlation (r=0.045). Patients with higher BMI had significantly improved OS when comparing the top 50% to bottom 50% (2.20 vs 1.89 years, p=0.03) and top 25% to bottom 25% (2.25 vs 1.84 years, p=0.03). When comparing patients classified as overweight or obese (BMI >/= 25) to those within normal range or below (BMI < 25), there was a trend towards increased OS (2.14 vs 1.90 years, p=0.075). There was no significant trend for BMI when comparing patients with higher OS with lower OS. There was also no significance for BMI on Cox proportional hazard multivariate analysis.

CONCLUSIONS

There was no significant linear correlation between BMI and survival for GBM patients, although there appears to be statistically significant improved survival benefit for patients with higher BMI compared to patients with lower BMI. Further investigation is warranted to explore this finding and if BMI could be used as a potential prognostic marker for GBM.

TMOD-27. A NEURAL CREST CELL SUBPOPULATION UNDERLIES INTRATUMOR HETEROGENEITY IN MENINGIOMA

BACKGROUND

Meningiomas are the most common primary intracranial tumor, and high grade meningiomas are resistant to most cancer therapies. Intratumor heterogeneity is a recognized source of resistance to treatment in numerous malignancies. Thus, we hypothesized that investigating molecular heterogeneity in meningiomas would elucidate biologic drivers and shed light on tumor evolution and mechanisms of resistance.

METHODS

We collected 86 spatially distinct samples at the time of resection from 13 meningiomas. Seven meningiomas were WHO grade I (46 samples), three were grade II (22 samples), and three were grade III (18 samples). Seven meningiomas were sampled at the time of salvage surgery (48 samples), and 6 were sampled at the time of initial diagnosis (38 samples). We performed multiplatform molecular profiling of these samples to identify drivers of intratumor heterogeneity, and validated our results using meningioma cells co-cultured with human cerebral organoids and RNA sequencing of paired primary and recurrent meningiomas.

RESULTS

Using bulk RNA sequencing, DNA methylation profiling and phylogenetic analysis of spatially distinct samples, we discovered significant transcriptomic, epigenomic and genomic heterogeneity in meningioma. In particular, we identified chromosomal structural alterations and differences in immune and neuronal signaling that underlie clonal evolution in high grade tumors. Using MRI-stratified bulk RNA sequencing, single nuclear RNA sequencing, RNA sequencing of paired primary and recurrent meningiomas, and live cell microscopy and single cell RNA sequencing of meningioma cells in co-culture with human cerebral organoids, we revealed a rare meningioma cell subpopulation with strong transcriptional concordance to the neural crest, a multipotent embryonic tissue that forms the meninges in development.

CONCLUSIONS

These data suggest that misactivation of a developmental cell population underlies intratumor heterogeneity in meningioma and that expression of neural crest and immediate early genes are an important step in meningeal oncogenesis.

NIMG-56. A MULTIMODAL 7 TELSA MRI INVESTIGATION OF LONG-TERM EFFECTS OF RADIOTHERAPY ON THE ADOLESCENT BRAIN & COGNITION

INTRODUCTION

Radiation therapy (RT) remains an integral role in the treatment of adolescent brain tumors, despite evidence of its long-term effects including cognitive impairment, vascular injury and reduced white matter integrity. While prior studies have related vascular injury to cognitive decline and associated more severe cognitive impairment with a whole-brain versus a focal RT approach, the relationship between underlying imaging, clinical, and treatment parameters has yet to be explored in this population. In this study we used multimodal 7 Tesla MR imaging to probe RT-induced changes in the brain and identified risk factors for clinical outcome.

METHODS

Twenty-three patients (age 6–25 years) with non-supratentorial tumors treated with RT as children and 4 nonirradiated control patients (ages 13–16 years) were scanned on a 7T MRI system; eight patients underwent serial imaging 0.9–3.7 years following the first scan. Simultaneous MR-veniography and angiography, and 90-direction, dual-shell multi-band diffusion MRI were used to assess the relationships among cerebral microbleed (CMB) development, changes in arterial radii, and whole-brain white matter connectivity. A computerized cognitive battery (Cogstate) evaluated multiple domains of cognitive function. Multiple univariate and multivariate regression models with multiple comparison corrections identified risk factors.

RESULTS

Cognitive status measured via executive function and working memory tasks revealed the strongest associations with type of RT and imaging parameters. Specific risk factors for worse outcome included whole-brain RT, RT at a younger age, and time since RT. On imaging this corresponded to increased CMB burden, decreased arterial volume, and reduced global structural connectivity; intrasubject serial imaging followed these trends.

CONCLUSION

7T-MRI was highly sensitive to CMBs with cumulative incidence rates greatly exceeding prior 3T studies in this population. This work demonstrates the value of multimodal 7T-MRI in providing metrics that reflect cognitive deficits arising from RT and identifying patients who would benefit the most from cognitive rehabilitation.

CMET-35. COMPETING RISKS ANALYSIS OF FACTORS INFLUENCING DEVELOPMENT OF LEPTOMENINGEAL METASTASIS IN BREAST CANCER PATIENTS RECEIVING STEREOTACTIC RADIOSURGERY FOR LIMITED BRAIN METASTASES

Leptomeningeal metastasis (LM) is a late stage manifestation of advanced breast cancer frequently managed with whole brain radiotherapy (WBRT) and/or intrathecal chemotherapy. A subset of breast cancer patients who undergo stereotactic radiosurgery (SRS) for limited brain metastases (BM) ultimately develop LM. We hypothesized that this subset of high-risk patients may be identified by patient, disease, and/or treatment parameters. Clinical records from 133 breast cancer patients from a single institution who underwent SRS for BM between February 2010 and March 2018 were retrospectively analyzed. Variables including histopathology, BM features, systemic disease burden, and prior treatments were analyzed. Cumulative incidence rates were estimated with death as a competing risk. Dichotomous variable cutoffs were based on the 75th percentile value. In our cohort, 27 (20.3%) patients ultimately developed LM. With a median follow up of 21.2 months after diagnosis of BM, the actuarial rate of LM at 24 months was 15.2% (95% CI, 8.7%-21.7%). Median OS after diagnosis of LM was 7.0 (95% CI, 3.1–15.4) months. There was significantly increased risk of LM with ≥9 vs < 9 BM at BM diagnosis (28.1% vs 10.8% [24-month actuarial risk], subdistribution HR 2.4, p=0.027), and ≥11 vs < 11 cumulative number of BM treated (25.7% vs 11.7% [24-month actuarial risk], subdistribution HR 2.7, p=0.01). Variables not significantly associated with the risk of LM included tumor receptor status (ER, PR, HER2, triple negative), graded prognostic assessment, KPS, extracranial metastases, total BM volume, prior WBRT, or prior surgical resection. Time intervals between SRS treatments immediately preceding LM diagnosis was not significantly different from other time intervals. In conclusion, patients with a larger number of brain metastases at BM diagnosis (≥9) or cumulatively treated (≥11) appear to be at higher risk of developing LM and may benefit from stronger consideration of WBRT, intrathecal chemotherapy, and/or brain-penetrating systemic therapy.

Diffusion Characteristics of Pediatric Diffuse Midline Gliomas with Histone H3-K27M Mutation Using Apparent Diffusion Coefficient Histogram Analysis

BACKGROUND AND PURPOSE

Diffuse midline gliomas with histone H3 K27M mutation are biologically aggressive tumors with poor prognosis defined as a new diagnostic entity in the 2016 World Health Organization Classification of Tumors of the Central Nervous System. There are no qualitative imaging differences (enhancement, border, or central necrosis) between histone H3 wildtype and H3 K27M-mutant diffuse midline gliomas. Herein, we evaluated the utility of diffusion-weighted imaging to distinguish H3 K27M-mutant from histone H3 wildtype diffuse midline gliomas.

MATERIALS AND METHODS

We identified 31 pediatric patients (younger than 21 years of age) with diffuse gliomas centered in midline structures that had undergone assessment for histone H3 K27M mutation. We measured ADC within these tumors using a voxel-based 3D whole-tumor measurement method.

RESULTS

Our cohort included 18 infratentorial and 13 supratentorial diffuse gliomas centered in midline structures. Twenty-three (74%) tumors carried H3-K27M mutations. There was no difference in ADC histogram parameters (mean, median, minimum, maximum, percentiles) between mutant and wild-type tumors. Subgroup analysis based on tumor location also did not identify a difference in histogram descriptive statistics. Patients who survived <1 year after diagnosis had lower median ADC (1.10 × 10^-3mm²/s; 95% CI, 0.90-1.30) compared with patients who survived >1 year (1.46 × 10^-3mm²/s; 95% CI, 1.19-1.67; P < .06). Average ADC values for diffuse midline gliomas were 1.28 × 10^-3mm²/s (95% CI, 1.21-1.34) and 0.86 × 10^-3mm²/s (95% CI, 0.69-1.01) for hemispheric glioblastomas with P < .05.

CONCLUSIONS

Although no statistically significant difference in diffusion characteristics was found between H3-K27M mutant and H3 wildtype diffuse midline gliomas, lower diffusivity corresponds to a lower survival rate at 1 year after diagnosis. These findings can have an impact on the anticipated clinical course for this patient population and offer providers and families guidance on clinical outcomes.

Estimating survival for renal cell carcinoma patients with brain metastases: an update of the Renal Graded Prognostic Assessment tool

Background

Brain metastases are a common complication of renal cell carcinoma (RCC). Our group previously published the Renal Graded Prognostic Assessment (GPA) tool. In our prior RCC study (n = 286, 1985-2005), we found marked heterogeneity and variation in outcomes. In our recent update in a larger, more contemporary cohort, we identified additional significant prognostic factors. The purpose of this study is to update the original Renal-GPA based on the newly identified prognostic factors.

Methods

A multi-institutional retrospective institutional review board-approved database of 711 RCC patients with new brain metastases diagnosed from January 1, 2006 to December 31, 2015 was created. Clinical parameters and treatment were correlated with survival. A revised Renal GPA index was designed by weighting the most significant factors in proportion to their hazard ratios and assigning scores such that the patients with the best and worst prognoses would have a GPA of 4.0 and 0.0, respectively.

Results

The 4 most significant factors were Karnofsky performance status, number of brain metastases, extracranial metastases, and hemoglobin. The overall median survival was 12 months. Median survival for GPA groups 0-1.0, 1.5-2.0, 2.5-3, and 3.5-4.0 (% n = 25, 27, 30 and 17) was 4, 12, 17, and 35 months, respectively.

Conclusion

The updated Renal GPA is a user-friendly tool that will help clinicians and patients better understand prognosis, individualize clinical decision making and treatment selection, provide a means to compare retrospective literature, and provide more robust stratification of future clinical trials in this heterogeneous population. To simplify use of this tool in daily practice, a free online application is available at brainmetgpa.com.

An Open-Source Tool for Anisotropic Radiation Therapy Planning in Neuro-oncology Using DW-MRI Tractography

There is evidence from histopathological studies that glioma tumor cells migrate preferentially along large white matter bundles. If the peritumoral white matter structures can be used to predict the likely trajectory of migrating tumor cells outside of the surgical margin, then this information could be used to inform the delineation of radiation therapy (RT) targets. In theory, an anisotropic expansion that takes large white matter bundle anatomy into account may maximize the chances of treating migrating cancer cells and minimize the amount of brain tissue exposed to high doses of ionizing radiation. Diffusion-weighted MRI (DW-MRI) can be used in combination with fiber tracking algorithms to model the trajectory of large white matter pathways using the direction and magnitude of water movement in tissue. The method presented here is a tool for translating a DW-MRI fiber tracking (tractography) dataset into a white matter path length (WMPL) map that assigns each voxel the shortest distance along a streamline back to a specified region of interest (ROI). We present an open-source WMPL tool, implemented in the package Diffusion Imaging in Python (DIPY), and code to convert the resulting WMPL map to anisotropic contours for RT in a commercial treatment planning system. This proof-of-concept lays the groundwork for future studies to evaluate the clinical value of incorporating tractography modeling into treatment planning.

RADI-21. STEREOTACTIC RADIOSURGERY FOR 10 OR MORE BRAIN METASTASES PROVIDES EXCELLENT RATES OF INTRACRANIAL DISEASE CONTROL WITH SUPERIOR HIPPOCAMPAL SPARING

BACKGROUND: Recent evidence supports hippocampal sparing during whole brain radiotherapy (HS-WBRT) to improve neurocognitive outcomes in patients with brain metastases (BM). This study sought to quantify the hippocampal dosimetry and treatment efficacy of stereotactic radiosurgery (SRS) to 10 or greater BM to clarify the roles of SRS and WBRT. METHODS: Patients at a single institution treated with SRS to 10 or more BM without WBRT from 1999 to 2016 were retrospectively reviewed. Treatment-related outcomes including overall survival (OS), freedom from progression (FFP), freedom from new metastases (FFNM), and adverse radiation effect (ARE) were quantified. Hippocampal volumes were retrospectively delineated and dosimetry was evaluated in patients treated with upfront SRS. RESULTS: 143 patients with a total of 2198 lesions met criteria for inclusion with 75 patients treated with upfront SRS and 68 treated as salvage from prior WBRT. Median age was 57 (IQR: 46–65) and median KPS 80 (IQR: 70–90). Histologies included breast (n=52), lung (n=49), melanoma (n=30), and other (n=12). Median number of lesions per patient was 13 (IQR 11–17) with median total volume of treatment of 4.1 cc (IQR 2.0–9.9). 12-month FFP per lesion for upfront and salvage treatment was 96.8% (95% CI: 95.5–98.1) and 83.6% (95% CI: 79.9–87.5) respectively (p < 0.001). 12-month FFNM for upfront and salvage FFSRS was 18.8% (95% CI: 10.9–32.3) versus 19.2% (95% CI: 9.7–37.8) respectively (p = 0.90). Mean hippocampal dose was 150 cGy (IQR 100–202). Symptomatic ARE was observed in 2% of patients or 1% of treated lesions. CONCLUSIONS: High rates of local control can be achieved when treating patients with greater than 10 BM with hippocampal doses that are dramatically lower than for HS-WBRT. Hippocampal sparing is readily achievable with expected rates of new metastatic lesions developing in treated patients with low rates of symptomatic ARE.

RADI-43. ARTERIAL SPIN LABELING PERFUSION MR IMAGING FOR DIFFERENTIATION BETWEEN TUMOR RECURRENCE AND PSEUDOPROGRESSION IN INTRACRANIAL METASTASES FOLLOWING STEREOTACTIC RADIOSURGERY

Stereotactic radiosurgery (SRS) is a standard adjuvant treatment for patients with limited intracranial metastatic disease. Transient growth, increased peritumoral edema, and inflammation can be seen in up to a third of these cases following SRS. Unfortunately, this pseudoprogression is often indistinguishable from true progression by morphologic MR imaging thereby complicating patient management. The purpose of this study was to evaluate whether arterial spin labeling (ASL) perfusion can differentiate tumor recurrence from pseudoprogression after SRS. We reviewed patients treated between 2013 and 2018 and identified 24 patients with 43 intracranial metastases who had imaging suggesting progression following SRS and also had ASL perfusion acquired at time of MR imaging. Median imaging follow-up was 11 months (range 3–64 months). Outcome of tumor recurrence or pseudoprogression was confirmed in each case by pathology or subsequent MR imaging. 25 (58%) lesions were classified as tumor recurrence (13, 52% by pathology), while 18 (42%) were classified as pseudoprogression (3, 18% by pathology). ASL perfusion values (normalized cerebral blood flow) were higher in patients with tumor progression (2.1 vs 1.1 ml/min/100g, p=0.003). No significant difference was observed between histology, time from radiotherapy, marginal dose, volume of lesion, or instances of repeat SRS treatments between groups. In conclusion, elevated blood flow by ASL perfusion was closely associated with the diagnosis of tumor recurrence after SRS. Patients with intracranial metastases undergoing SRS may benefit from this short non-contrast sequence at time of follow-up MR imaging.

LPTO-05. FACTORS INFLUENCING RISK OF LEPTOMENINGEAL METASTASIS IN BREAST CANCER PATIENTS RECEIVING STEREOTACTIC RADIOSURGERY FOR LIMITED BRAIN METASTASES

Leptomeningeal metastasis (LM) is a late stage manifestation of advanced breast cancer frequently managed with whole brain radiotherapy (WBRT) and/or intrathecal chemotherapy. A subset of breast cancer patients who undergo stereotactic radiosurgery (SRS) for limited brain metastases (BM) ultimately develop LM. We hypothesized that this subset of high-risk patients may be identified by patient, disease, and/or treatment parameters. Clinical records from 135 consecutive breast cancer patients from a single institution who underwent SRS for BM between February 2010 and March 2018 were retrospectively analyzed. Diagnosis of LM was determined radiographically and/or by cerebrospinal fluid analysis. Demographic data, clinical history, histopathology, BM features, systemic disease burden, and prior treatments were analyzed with Cox proportional hazards regression. In our cohort, 22 (16.3%) patients ultimately developed LM. With a median follow up of 18.9 (IQR 8.6–38.7) months after diagnosis of BM, the actuarial rate of LM at 18 months was 14.5% (95% CI, 7.0–21.4%). Median OS after diagnosis of LM was 7.3 (95% CI, 3.1–15.4) months. There was significantly increased risk of LM with ≥5 vs < 5 BM at BM diagnosis (33.0% vs 7.5% [18-month actuarial risk], HR 3.5, p=0.0045), and ≥7 vs < 7 cumulative number of BM treated (21.9% vs 11.1% [18-month actuarial risk], HR 2.7, p=0.023). Variables not significantly associated with the risk of LM included tumor receptor status (ER, PR, HER2, triple negative), graded prognostic assessment, KPS, extracranial metastases, total BM volume, prior WBRT, or prior surgical resection. In conclusion, patients with a larger number of brain metastases at BM diagnosis or ≥7 cumulative number of brain metastases treated appear to be at higher risk of developing LM and may benefit from stronger consideration of WBRT, intrathecal chemotherapy, and/or brain-penetrating systemic therapy.

RADI-31. MULTI-INSTITUTIONAL VALIDATION OF BRAIN METASTASIS VELOCITY, A RECENTLY DEFINED PREDICTOR OF OUTCOMES FOLLOWING STEREOTACTIC RADIOSURGERY

INTRODUCTION: Brain metastasis velocity (BMV) is a prognostic metric that describes the recurrence rate of new brain metastases after initial treatment with radiosurgery (SRS). We have previously risk stratified patients into high, intermediate, and low-risk BMV groups, which correlates with overall survival (OS). We sought to externally validate BMV in a multi-institutional setting. METHODS: Patients from nine academic centers were treated with upfront SRS; the validation cohort consisted of data from eight institutions not previously used to define BMV. Patients were classified by BMV into low (< 4 BMV), intermediate (4–13 BMV), and high-risk groups (>13 BMV). Time-to-event outcomes were estimated using the Kaplan-Meier method. Cox proportional hazards methods were used to estimate the effect of BMV and salvage modality on OS. RESULTS: Of 2829 patients, 2092 patients were included in the validation dataset. Of these, 921 (44.0%) experienced distant brain failure (DBF). Median OS from initial SRS was 11.2 mo. Median OS for BMV < 4, BMV 4–13, and BMV > 13 were 12.5 mo, 7.0 mo, and 4.6 mo (p < 0.0001). Compared to initial salvage with WBRT, salvage SRS was associated with improved OS following DBF for BMV < 4 (p = 0.05), BMV 4–13 (p = 0.002) and BMV > 13 (p = 0.0001). CONCLUSIONS: This multi-institutional dataset validates BMV as a predictor of OS following initial SRS. BMV is being utilized in upcoming multi-institutional randomized controlled trials as a stratification variable for salvage whole brain radiation vs salvage SRS after DBF.

Estimating survival in patients with gastrointestinal cancers and brain metastases: An update of the graded prognostic assessment for gastrointestinal cancers (GI-GPA)

Background

Patients with gastrointestinal cancers and brain metastases (BM) represent a unique and heterogeneous population. Our group previously published the Diagnosis-Specific Graded Prognostic Assessment (DS-GPA) for patients with GI cancers (GI-GPA) (1985-2007, n = 209). The purpose of this study is to update the GI-GPA based on a larger contemporary database.

Methods

An IRB-approved consortium database analysis was performed using a multi-institutional (18), multi-national (3) cohort of 792 patients with gastrointestinal (GI) cancers, with newly-diagnosed BM diagnosed between 1/1/2006 and 12/31/2017. Survival was measured from date of first treatment for BM. Multiple Cox regression was used to select and weight prognostic factors in proportion to their hazard ratios. These factors were incorporated into the updated GI-GPA.

Results

Median survival (MS) varied widely by primary site and other prognostic factors. Four significant factors (KPS, age, extracranial metastases and number of BM) were used to formulate the updated GI-GPA. Overall MS for this cohort remains poor; 8 months. MS by GPA was 3, 7, 11 and 17 months for GPA 0-1, 1.5-2, 2.5-3.0 and 3.5-4.0, respectively. >30% present in the worst prognostic group (GI-GPA of ≤1.0).

Conclusions

Brain metastases are not uncommon in GI cancer patients and MS varies widely among them. This updated GI-GPA index improves our ability to estimate survival for these patients and will be useful for therapy selection, end-of-life decision-making and stratification for future clinical trials. A user-friendly, free, on-line app to calculate the GPA score and estimate survival for an individual patient is available at brainmetgpa.com.

Survival and prognostic factors in patients with gastrointestinal cancers and brain metastases: have we made progress?

The literature describing the prognosis of patients with gastrointestinal (GI) cancers and brain metastases (BM) is sparse. Our group previously published a prognostic index, the Graded Prognostic Assessment (GPA) for GI cancer patients with BM, based on 209 patients diagnosed from 1985-2005. The purpose of this analysis is to identify prognostic factors for GI cancer patients with newly diagnosed BM in a larger contemporary cohort. A multi-institutional retrospective IRB-approved database of 792 GI cancer patients with new BM diagnosed from 1/1/2006 to 12/31/2016 was created. Demographic data, clinical parameters, and treatment were correlated with survival and time from primary diagnosis to BM (TPDBM). Kaplan-Meier median survival (MS) estimates were calculated and compared with log-rank tests. The MS from time of first treatment for BM for the prior and current cohorts were 5 and 8 months, respectively (P < 0.001). Eight prognostic factors (age, stage, primary site, resection of primary tumor, Karnofsky Performance Status (KPS), extracranial metastases, number of BM and Hgb were found to be significant for survival, in contrast to only one (KPS) in the prior cohort. In this cohort, the most common primary sites were rectum (24%) and esophagus (23%). Median TPDBM was 22 months. Notably, 37% (267/716) presented with poor prognosis (GPA 0-1.0). Although little improvement in overall survival in this cohort has been achieved in recent decades, survival varies widely and multiple new prognostic factors were identified. Future work will translate these factors into a prognostic index to facilitate clinical decision-making and stratification of future clinical trials.

Development and Implementation of a Simulation-Based Educational Workshop on Gynecological Brachytherapy: Pilot Study at a National Meeting

PURPOSE

Despite the importance of brachytherapy in the curative treatment of locally advanced cervical cancer, reviews of practice patterns in the United States have identified a decline in brachytherapy use in clinically appropriate patient populations. A survey of radiation oncologists identified lack of time and lack of guidance as barriers. To address these barriers, the purpose of this study was to develop a simulation-based educational (SBE) gynecologic brachytherapy workshop.

METHODS AND MATERIALS

The SBE gynecologic brachytherapy workshop was developed with expertise from 2 institutions, combining procedural simulation with a practical discussion of brachytherapy applicator insertion techniques. The primary outcome was feasibility of workshop deployment, defined as completion of all workshop components in the time allotted. Preworkshop and postworkshop surveys were also administered to assess efficacy, a secondary outcome.

RESULTS

The workshop took place at a national radiation oncology meeting, and all workshop components were completed in the 2 hours allotted. SBE stations focused on (1) fiducial placement, (2-3) applicator selection, (4) suturing, and (5) pelvic examination and applicator placement. Fourteen participants completed surveys. Respondents included residents and attending physicians. More than 50% of respondents were from academic practices and practiced gynecologic brachytherapy weekly or more. Curricular objectives for this workshop were for ≥20% trainees to report increased confidence in practice and ≥20% of trainees to report increased familiarity with applicators. After participation in the workshop, confidence in applicator choice improved in 9 of 13 participants (69%), confidence in complication management improved in 8 of 13 participants (62%), and familiarity with applicators improved in 7 of 13 participants (54%). These differences were statistically significant at α = .05.

CONCLUSIONS

This study demonstrated feasibility in using simulation for gynecologic brachytherapy education at a national meeting. Although most respondents were experienced in brachytherapy, more than half reported increased confidence and familiarity with aspects of the procedure after the workshop. Future work should address interstitial needle placement and improved time management of workshop stations.