Integration of an App-Based Cognitive Evaluation Program into Radiosurgery Practice: Outcomes and Patient Survey Analysis from a Prospective Observational Study

PURPOSE/OBJECTIVE(S)

Cognitive decline is a significant consequence of stereotactic radiosurgery (SRS) in patients with brain metastases. This is often underrecognized and understudied outside of a formal clinical trial setting as traditional methods are often logistically difficult and need specialized personnel and additional time. To address these challenges, we implemented a prospective study (NCT05504681), incorporating an innovative app-based solution to monitor patient assessments over time, collect patient data easily, and be suitable for cross-cultural use in multiple languages for monitoring post-SRS cognitive decline.

MATERIALS/METHODS

Patients undergoing SRS from December 2021 to October 2022 were enrolled in this study and completed feedback surveys. The assessments consisted of learning and memory (Hopkins verbal learning test-revised [HVLT-R]), attention and processing speed (Digit symbols modalities test [SDMT]), verbal fluency (Controlled oral word association test [COWAT]) and executive function (Trail making test [TMT]). Baseline and 3-month follow-up testing were conducted in conjunction with routine imaging and clinical assessments. Neurocognitive deterioration (ND) was defined as a decrease of ≥2 standard errors of the mean in any of the tests, without evidence of new intracranial disease. Any differences between the baseline and follow-up assessments were confirmed using the reliable change index.

RESULTS

A total of 30 patients with median age of 68 (range: 47-87) were enrolled. The median KPS was 90 and 60% were female. 43% of participants had a high school or equivalent level of education. 19 (63%) patients were Hispanic and 43% tested in Spanish. The median number of treated lesions was 2 (1-13) and 7 (23%) patients were treated to ≥5 lesions. The median mean left and right hippocampal doses were 0.3 Gy (0-3 Gy) and 0.2 Gy (0-5.2 Gy), respectively. Overall, 50% of patients met criteria for ND at 3 months. 20% of patients showed ND in HVLT-R-immediate recall (IMM), 23% in HVLT-R-delayed recall (DR), 13% in HVLT-R-recognition (Rec), 3% in COWAT and 20% in TMT. None of the patients had ND in SDMT. The mean relative decline was 28% for HVLT-R- IMM, 34% for HVLT-R-DR, 6% for HVLT-R- Rec, 25% for COWAT, and 21% for TMT. There was no significant association between the number of treated lesions and ND. Based on the feedback results, the majority of patients found the system easy to use (94%) and relevant to their care (73%). Most patients reported that app-based evaluation improved discussions with clinicians (77%), made them feel more in control of their care (79%), and they would recommend the system to other patients (87%).

CONCLUSION

Our study showed a high incidence of ND using an app-based tool in a patient who underwent SRS and from diverse education and language backgrounds. Patient survey results demonstrated that the tool was easy to use and relevant to the patient's care, especially due to improvements in discussions with clinicians and a sense of being in control of their own care.

Stereotactic Radiosurgery for Small Intact Brain Metastasis: A Comparative Evaluation of 3 Different Single Fraction Prescription Doses

PURPOSE/OBJECTIVE(S)

While single-fraction stereotactic radiosurgery (SRS) in the treatment of small brain metastases (SBM, ≤ 2 cm) is well established, prescription dosing varies considerably across institutions and clinical trials. The choice of prescription dose is a delicate balance between local failure (LF) and radiation necrosis (RN) risks. In the modern era, historically-established dosing thresholds may no longer be applicable. To evaluate the impact of prescription dose on outcomes, we performed a comparative analysis of patients with SBM treated with definitive SRS using three different prescriptions, at a single tertiary institution.

MATERIALS/METHODS

Consecutive patients with intact SBM treated with SRS from January 2017 and December 2021 were analyzed. Baseline patient characteristics and dosing parameters were abstracted from the medical record. To limit the integral brain dose when treating multiple brain metastases, the institutional practice was to reduce prescription dose as the total number of lesions increased (i.e., 24 Gy for ≤10 lesions, 22 Gy for 11-20, and 20 Gy for >20). A per lesion analysis, where each lesion was followed from the date of SRS to the last follow-up, was conducted with primary endpoints of LF and RN. Gray's test was used to compare the cumulative incidence of the LF and RN, with death as a competing risk. Factors affecting LF were analyzed using Cox hazard regression analysis.

RESULTS

A total of 1318 SBM in 250 patients received SRS and met the inclusion criteria. The median age was 62 years (range: 18-90), median KPS was 90 (range: 50-100) and 66% were female. The most common primary tumors were lung (55.5%) and breast cancers (26.4%). With a median follow-up of 12 months, 136 (11%) LF in 44 patients and 70 (5.7%) RN events in 46 patients occurred. The actuarial 1-year cumulative rate of LF was lower in lesions treated with 24 Gy (6.4%, 95% CI: 4.7-8.6%) or 22 Gy (5.8%, 95% CI: 3.7-8.7%) compared to 20 Gy (15.4%, 95% CI: 10.9-20.5%) (p<0.01). 22 Gy and 24 Gy prescription doses were associated with a 44% and 52% reduction in risk in LF compared to 20 Gy (HR: 0.56; 95% CI: 0.36-0.9; p = 0.01 and HR: 0.48; 95% CI: 0.31-0.74; p<0.01, respectively). In a subset analysis of radiosensitive tumors, 1-year LF rate was still lower with 24 Gy (7.4%, 95% CI: 5.3-9.9%) and 22 Gy (6.1%, 95% CI: 3.7-9.4%) than 20 Gy (15.7%, 95% CI: 11.2-21%) (p = 0.01). The cumulative 1-year RN rate numerically declined with dose, but was not statistically significantly different, with 3.6% (95% CI: 2.3-5.3%) for 24 Gy, 2.6% (95% CI: 1.3-4.8%) for 22 Gy and 1.4% (95% CI: 0.4-3.7%) for 20 Gy.

CONCLUSION

Patients treated with single fraction SRS to intact SBM were at increased risk of LF with prescription doses of 20 Gy compared to 22-24 Gy, without an increased risk of RN. Even in patients with radiosensitive histologies, higher LF rates were still observed following 20 Gy compared to 22-24 Gy.

A Comparison of Local Failure and Necrosis Following Different Radiosurgery Strategies for Large Brain Metastases

PURPOSE/OBJECTIVE(S)

Large brain metastases (LBMs) are associated with poor local control with single-fraction stereotactic radiosurgery (SRS) alone. Various alternative strategies have been developed, including fractionated SRS (FSRS) and staged SRS (SSRS) for intact LBMs, and resection with postoperative-SRS (postop-SRS) or preoperative-SRS (preop-SRS) for operable LBMs. The objective of this study is to compare local failure (LF) and radiation necrosis (RN) outcomes among these four management strategies to determine the optimal treatment paradigm.

MATERIALS/METHODS

Consecutive patients diagnosed with LBM (≥2 cm in maximum dimension) between July 2017 and January 2022 and treated with one of the aforementioned strategies at a single tertiary institution were evaluated. All immobilization, target contouring, margins, dose- and prescription selection followed pre-defined institutional guidelines. Primary endpoints included LF, symptomatic RN, or a composite endpoint of these two variables. Gray's test was used to compare the cumulative incidence of the LF and the composite endpoint, with death as a competing risk.

RESULTS

A total of 234 LBMs in 188 consecutive patients met the inclusion criteria. The median age was 65 years (range: 31-98), the median KPS was 80 (range: 50-100), and 58% were female. The most common primary tumors were lung (48%) and breast cancer (17%). The median maximum tumor diameter was 3.0 cm (range: 2.0-5.6). 47 (20%) lesions were treated with FSRS, 66 (28%) with SSRS, 74 (32%) with postop-SRS, and 47 (20%) with preop-SRS. With a median follow-up of 12 months, 22 (9%) LF and 11 (5%) RN events occurred. The 6-month and 1-year cumulative incidences of LF for the entire cohort were 5% (95% CI: 3%-9%) and 8% (95% CI: 5%-12%), respectively. The 6-month and 1-year LF rates were 4% (95% CI: 1%-13%) and 8% (95% CI: 3%-20%) for FSRS; 8% (95% CI: 3%-20%) and 8% (95% CI: 3%-20%) for SSRS; 7% (95% CI: 3%-15%) and 8% (95% CI: 3%-16%) for postop-SRS; 0 and 7% (95% CI: 2%-20%) for preop-SRS (p>0.05). The 1-year OS rates were favorable in resected patients (61% for postop-SRS and 82% for preop-SRS) compared to SRS alone strategies (45% for FSRS and 56% for SSRS) (p = 0.004). Similarly, RN events were significantly lower in resected patients treated with either bimodality approach (0 for postop-SRS and 4% for preop-SRS) than SRS standalone strategies (9% for FSRS and 8% SSRS) (p = 0.024). At 12 months, the cumulative probabilities of the composite endpoint were 13% (95% CI: 5%-25%) for FSRS, 15% (95% CI: 7%-25%) for SSRS, 9% (95% CI: 3%-17%) for postop-SRS, and 12% (95% CI: 4%-24%) for preop-SRS and not significantly different between the groups.

CONCLUSION

For medically operable patients with surgically resectable LBMs, a strategy of surgery and SRS, regardless of timing, is associated with favorable local control and reduced risk for RN. For unresected patients, either SSRS or FSRS is associated with similar local control, but slightly higher RN risk. Prospective comparative evaluation is warranted.

Surgically Targeted Radiation Therapy (STaRT) for Brain Metastases: Initial Experience from a Prospective Multi-Institutional Registry

PURPOSE/OBJECTIVE(S)

Resection and intraoperative brachytherapy for patients with large, operable brain metastasis allows for both relief of mass effect and the delivery of radiotherapy (RT) to the resection cavity with a favorable dosimetric profile. The objective of this study was to analyze early patterns-of-care and treatment-related toxicity outcomes for brain metastasis patients treated with surgically targeted radiation therapy (STaRT) using a novel brachytherapy carrier.

MATERIALS/METHODS

Patients with brain metastasis, de novo and recurrent disease, who enrolled onto a prospective multi-institutional observational study (NCT04427384) were the subject of this analysis. Patients underwent resection and immediate implantation of bioresorbable, conformable, 20 mm x 20 mm x 4 mm collagen tile brachytherapy device(s) containing four uniform-intensity Cesium-131 sources. Toxicities were categorized using the CTCAE v5.0 adverse event (AE) criteria.

RESULTS

From 10/2020 to 01/2023, 13 participating sites enrolled and treated 48 patients with 51 metastases (13 with de novo and 35 patients with recurrent brain metastases), and 3 patients had 2 lesions implanted at the same procedure. Median age was 61 years (range: 28-80), 52% were female, and the most common primary types were lung (56%) and breast (13%). The median maximum pre-operative dimension was 3.4 cm (range: 1.7-5.7) and median pre-operative tumor volume 13.7cm3 (range: 1.7-132). 64% had received prior RT with a median time from last RT to STaRT of 14.6 months range: 3.5-57.3). Median KPS at screening was 80 (range: 50-100), and remained stable at post op visit (80, range: 50-100), and at 3-months following treatment (80, range 50-100), respectively (p>0.05). The median time for implantation was 3 minutes (range: 0.4-30). At a median follow-up of 4 months (range: <1-18), no patient experienced a radiation-attributed AE, and only 1 attributable Gr >3 AE was noted (Gr 5 intracerebral hemorrhage deemed probably related to surgery and unrelated to the implanted device).

CONCLUSION

Early results from this prospective multi-center trial demonstrate the feasibility and safety of STaRT. The lack of radiation-related AE, even with short follow-up, is intriguing given the relatively large lesion size and proportion of patients treated for recurrent, previously irradiated disease. Additional follow-up will provide data on tumor control outcomes and radiation necrosis rates using this novel technique.

Advancing beyond the Hippocampus to Preserve Cognition for Patients with Brain Metastases: Dosimetric Results from a Phase 2 Trial of Memory-Avoidance Whole Brain Radiotherapy

PURPOSE/OBJECTIVE(S)

Recent advances to preserve neurocognitive function in patients treated for brain metastases include stereotactic radiosurgery (SRS), hippocampal avoidance whole brain radiation therapy (HA-WBRT), and memantine administration. However, 23% of patients receiving HA-WBRT and memantine on NRG-CC001 still experienced executive function deterioration at 4 months, with 12% experiencing total recall and delayed recognition deterioration at 6 months. The hippocampus, corpus callosum, fornix, and amygdala are key neurocognitive substructures with a low propensity for brain metastases. Herein, we report our preliminary experience using an advanced "memory-avoidance" WBRT (MA-WBRT) approach sparing these substructures for patients with multiple (>15) brain metastases.

MATERIALS/METHODS

Ten consecutive patients treated with MA-WBRT on a phase 2 clinical trial (OSU-21074) were reviewed. In each patient, the hippocampi, amygdalae, corpus callosa, and fornix were contoured. Patients were not eligible for MA-WBRT if they had metastases in these substructures. A memory- avoidance region created using a 5mm volumetric expansion around these substructures. Hotspots were avoided in the hypothalamus and pituitary gland. Dose constraints for these avoidance structures were modeled after NRG CC-001 and include a D100% ≤ 9 Gy and a D0.03 cc ≤ 16 (acceptable to 20 Gy). Coverage of brain metastases was prioritized over memory avoidance dose constraints. Linac-based volumetric modulated arc therapy (VMAT) plans were generated for a prescription dose of 30 Gy in 10 fractions.

RESULTS

On average, the memory avoidance structure volume was 37.1 ccs (Range: 25.2-44.6 ccs), occupying 2.5% of the entire whole brain target volume. All treatment plans met the D100% dose constraint, and 8/10 plans met the D0.03cc constraint, with priority given to tumor coverage for the remaining 2 cases. VMAT spared the memory avoidance structures with a median dose range of 10.8-14.2 Gy and a maximum dose (D0.03cc) range of 15.6-22.7 Gy. The mean dose to the memory avoidance structures was 12.7 Gy (Range: 11.5-13.8 Gy). Target coverage (D98% > 25 Gy) and homogeneity (D2% ≤ 37.5 Gy) were achieved for all plans.

CONCLUSION

Modern VMAT techniques allow for sparing of the hippocampus, amygdala, corpus callosum, and fornix with good target coverage and homogeneity. Prospective quality of life and cognitive data including are being collected and include the Functional Assessment of Cancer Therapy - Brain (Fact-Br), Hopkins Verbal Learning Test (HLVT-R), Trail Making Test A/B (TMT-A/B) and Controlled Oral Word Association Test (COWAT). After enrollment is completed, these data will be evaluated to assess the efficacy of MA-WBRT to mitigate declines in quality of life and cognition after whole brain radiation.

Outcomes of MR-Guided Stereotactic Body Radiotherapy (MRgSBRT) for Adrenal Metastases: A Multi-Institutional Pooled Analysis

PURPOSE/OBJECTIVE(S)

Stereotactic body radiotherapy (SBRT) is an effective treatment for adrenal metastases, but it is technically challenging and there are concerns about toxicity due to the proximity of organs at risk. We hypothesized that MR-guided SBRT (MRgSBRT) using a 0.35 T MR-Linac for adrenal metastases can achieve durable local control (LC) with a low probability of toxicity.

MATERIALS/METHODS

In an ethics-approved study, we analyzed clinical and dosimetric data of patients treated with MRgSBRT at 10 institutions between 2016-2022. LC, local progression-free survival (LPFS), distant progression-free survival (DPFS) and overall survival (OS) were estimated using Kaplan-Meier method and log-rank test. Responses were evaluated using RECIST criteria. Toxicity was graded according to CTCAE (v4.0). OS and DPFS were calculated on a per-patient basis, while LC and LPFS were calculated on a per-lesion basis.

RESULTS

A total of 249 patients (260 adrenal lesions) were included; median age was 65 years (range 28-91), 65.5% were male, 83.9% had ECOG PS 0-1. The most common primary tumor was lung cancer (69.1%). Adrenal metastases were synchronous, metachronous, oligoprogressive or oligopersistent in 20%, 41.5%, 35.8% and 2.7% of patients, respectively. Metastatic pattern was solitary in 26.9%, oligometastatic in 57.3% and polymetastatic in 15.8% of patients. Right-sided metastases comprised 40%, left-sided 51.5% and lesions were bilateral in 8.5%. Chemotherapy and immunotherapy were administered in 67.1% and 60.6% of patients, respectively. Median gross tumor volume was 21.8 cc (range 1.1-383.2) and median planning target volume was 36.9 cc (range 3.6-516.9). Median total dose was 45 Gy (range 16-60), median fraction number was 5 (range 1-8) and median fraction dose used was 10 Gy (range 5-24). Median BED10 was 100 Gy (range 37.5-132); 87.8% of fractions used adapted plans. At a median follow-up was 17.7 months (IQR 5.5-21.7), local responses were scored as complete response (CR), partial response (PR), stable disease (SD) or progressive disease (PD) in 36.9%, 28.2%, 25.7%, and 9.1%, respectively. Median OS was 30.4 months, with 1- and 2- year OS rates of 75.3% and 57.1%, respectively. On multivariate analysis, significantly higher OS rates were seen in patients achieving a CR (p = 0.007, HR 0.50) and with ECOG scores of 0-1 (p = 0.001, HR 0.43). One- and 2- year LPFS rates were 94.5% and 88.8%, respectively. No local recurrences were observed after treatment to a BED10>100 or with single fraction (range 16-24 Gy). Only 2 patients (0.8%) had ≥grade 3 chronic toxicity.

CONCLUSION

This multi-institutional study of MRgSBRT outcomes for adrenal metastases revealed a 2-year LPFS of 89%, with a <1% risk of ≥grade 3 toxicity. Daily adaptation was performed in 90% of plans, indicating a beneficial role for MR guidance.

Patterns of Locoregional Failure After Ablative 5-Fraction Stereotactic MR-Guided on-Table Adaptive Radiation Therapy for Pancreatic Cancer

PURPOSE/OBJECTIVE(S)

SBRT for pancreatic ductal adenocarcinoma (PDAC) is routinely delivered with non-ablative dose to only gross disease resulting in locoregional failure (LRF) rates of >50%, most commonly near the celiac artery (CA) and/or superior mesenteric artery (SMA). It is unclear whether an alternative approach of prescribing ablative dose to gross disease plus elective coverage prevents and/or delays LRF. The study objective was to describe the incidence and anatomic distribution of LRF using this treatment approach.

MATERIALS/METHODS

A single institution retrospective analysis was performed of non-metastatic PDAC patients who received ablative stereotactic MR-guided on-table adaptive radiation therapy (A-SMART) on a 0.35T MR-Linac from 2018-2022. Median prescribed dose was 50 Gy/5 fractions. Elective coverage (EC), including a margin around the primary tumor, CA, and SMA, to 33-35 Gy/5 fractions became routine in 2019 using a simultaneous integrated boost; the porta hepatis was not routinely covered. LRFs were contoured and defined as out-of-field (OOF), marginal (M), or in-field (IF) if >80%, 20-80%, or <20% of it was outside of the most peripheral prescription isodose line.

RESULTS

One hundred four patients were evaluated (87% head tumors). 94% had induction chemotherapy (median 4 months), usually FOLFIRINOX (66%) or gemcitabine/nab-paclitaxel (27%). 88% received EC. Median GTV, CTV, PTVgrosstumor, and PTVelective volumes were 29 cc, 90 cc, 64 cc, and 127 cc, respectively. 16 patients (15%) had LRF after a median of 17 months (range: 2.4-30.8) from A-SMART; 13 had scans available for delineating LRF. Median follow-up from A-SMART for the entire cohort vs. LRF was 12 vs. 24 months. LRF involved the primary tumor (31%), retroperitoneal lymph nodes (25%), SMA (19%), porta hepatis (19%), and CA (6%). LRF was OOF, M, or IF in 30.8% (n = 4), 61.5% (n = 8), and 7.7% (n = 1). Distance from the 3 SMA failures to SMA origin was 10 cm (EC used), 9.3 cm (EC used), and 3 cm (no EC). The 1 CA failure involved the CA origin (no EC). Median mean, maximum, and minimum dose of the contoured LRF region on the original plan was 33.3 Gy (range: 9.7-50.3 Gy), 56 Gy (range: 44.2-71.4 Gy), and 11.4 Gy (range: 1.2-22.7 Gy), respectively. Median V20, V25, V30, V35, and V40 of the contoured LRF was 84.3% (range: 16.1-100%), 69.2% (range: 12.5-99.7%), 57.5% (range: 9.3-95.5%), 41.2% (range: 6.8-84.0%), and 32.7% (range: 4.8-71.8%).

CONCLUSION

This study represents the first patterns of LRF analysis after ablative 5-fraction SBRT for PDAC. Although EC is not currently endorsed by published pancreas SBRT guidelines, our low LRF incidence especially involving the CA/SMA demonstrates that EC should be considered, even when delivering ablative dose. Furthermore, given that nearly all LRF were M or OOF we have considered expanding our institutional elective volumes. While the optimal EC dose is uncertain, 33-35 Gy appears effective in limiting IF LRF and therefore has been standardized within ongoing ablative SBRT trials for PDAC at our institution.

Ablative 5-Fraction CT vs. MR-Guided Pancreatic SBRT: Evaluation of Interfraction Anatomic Changes on Dosimetric Constraints

PURPOSE/OBJECTIVE(S)

CT-guided SBRT for locally advanced pancreatic cancer (LAPC) is usually non-ablative (BED < 100 Gy10) to minimize grade 3+ toxicity risks given the concern of interfraction anatomic changes (IACs) in GI anatomy and imaging quality associated with kV-CBCT. Emerging data demonstrate that MR guidance facilitates 5-fraction (fx) dose escalation due to superior soft tissue contrast, continuous intrafraction imaging, automatic beam gating, and on-table adaptive replanning capability. Treatment outcomes for ablative 5-fx CT- vs. MR-guided SBRT are not well characterized, nor are differences in predicted GI OAR doses when accounting for IACs.

MATERIALS/METHODS

Weevaluated 40 plans (20 CT, 20 MR) for 20 LAPC patients (pts) previously treated in breath hold (BH) on a 0.35 T MR-Linac. Prescribed dose was 50 Gy (gross disease) and 33 Gy (elective) in 5 fx using a simultaneous integrated boost technique. CT plans were retrospectively created using 2-3 VMAT arcs with the same prescription dose, target volumes (assuming BH), and constraints (prioritizing OARs over target coverage) as the MR IMRT plans (∼20-40 fields). CT planners were blinded to MR plans. We compared predicted GI OAR dose of CT vs. MR plans across each of the 5 fx for all 20 patients to evaluate the dosimetric impact of IACs by coregistering CT plans to the anatomy of the day based on 0.35T MR scans acquired for GI OAR segmentation and treatment delivery.

RESULTS

MedianV100% of the GTV, CTV, PTV50, and PTV33 across the original CT vs. MR plans were 97.5% vs. 91.3% (p = 0.017), 99.9% vs. 98.2% (p<0.01), 86.2% vs. 79.3% (p = 0.39), and 97.2% vs. 93.0% (p<0.01), respectively. GI OAR constraints were met for all original CT/MR plans although it was predicted that 1+ GI OAR constraint would be violated (most commonly duodenum) for 88/100 CT vs. 85/100 MR fractions. Across the 88 violated CT fractions, the median predicted GI OAR doses were duodenum V35: 3.3 cc (range: 0.16-18.0cc), duodenum V40: 1.2 cc (range: 0.01-11.9cc), small bowel V35: 1.2 cc (range: 0.4-10.9cc), small bowel V40: 0.2 cc (range: 0.04-7.0cc), stomach V35: 1.5 cc (range: 0.52-6.8cc), stomach V40: 0.3 cc (range: 0.05-2.8cc). GI OAR doses across the 85 violated MR fractions were similar. Median fxs per pt with 1+ predicted GI OAR violation was 5 (range: 1-5) for both CT and MR plans.

CONCLUSION

This isthe first evaluation of IAC effects on predicted GI OAR dose for 5-fx CT- vs. MR-guided SBRT. Although VMAT arcs facilitated higher target coverage in the initial CT plans, GI OAR constraint violations were observed in 85-88% of CT/MR plans. Although on-table adaptive replanning is routine on MR-guided Linacs it is not commonly available on CT-guided Linacs. As such, ablative 5-fx SBRT delivered with CT guidance is expected to result in significant toxicity due to exceeding GI OAR constraints for most delivered fractions.

Characterization of Large Brain Metastases with 18F-Fluciclovine PET/CT Treated with Staged Stereotactic Radiosurgery (SSRS): Phase 1 Proof-of-Concept Interim Analysis

PURPOSE/OBJECTIVE(S)

Single-session stereotactic radiosurgery (SRS) for large brain metastases (>2cm) results in modest local control. Temporally staged SRS (SSRS), whereby 2 stages of SRS are delivered over a time interval of several weeks, is a novel strategy associated with improved control rates and acceptable radiation necrosis rates. Biomarkers for response are lacking. Here, we report interim results of a phase 1, proof-of-concept study (NCT04689048) to assess the potential clinical utility of amino acid radiotracer 18F-fluciclovine PET/CT as a functional integral biomarker for patients with large brain metastases treated with SSRS.

MATERIALS/METHODS

Patients with previously untreated large brain metastases (≥1 lesion; >2cm) underwent a baseline (pre-treatment) 18F-fluciclovine PET/CT and contrast-enhanced treatment planning brain MRI immediately before first SSRS (15 Gy), an interim PET/CT + MRI (4 weeks after the 1st SSRS, immediately prior the 2nd SSRS [15 Gy]), and post-treatment PET/CT + MRI (8 weeks after 2nd SSRS). This interim analysis reviewed the imaging characteristics from static PET images acquired 10-25 minutes after 18F-fluciclovine injection, for the first 7 enrolled patients who completed baseline imaging and 5 who completed the entire treatment course.

RESULTS

Seven patients completed baseline imaging and were treated with SSRS for 9 protocol-eligible target lesions, and an additional 25 bystander lesions were treated with SRS. The median age was 72 years and 57% were female. All lesions > 5 mm exhibited baseline increased 18F-fluciclovine uptake compared to the normal contralateral brain. The median baseline target lesion diameters and volumes were 2.16 cm (1.76-3.22 cm) and 4.71cc (2.24-10.21 cc). The median baseline SUVmax, SUVpeak, and SUVmean values were 5.78 (2.16-8.79), 3.33 (0.5-2.72), and 1.75 (1.22-5.16), respectively. The median relative reduction in diameter and volume were both 2% (-13% to 23% and -30% to 60%, respectively) at the interim scans, and at the first follow-up were 30% (-0.2% to 44%) and 43% (-13% to 94%), respectively. Corresponding median relative reduction values for SUVmax, SUVpeak, and SUVmean at interim scans were 20% (-174%-73%), 9% (-99% to 75%), and 14% (-36% to 69%), and at first follow-up 59% (21% to 87%), 41% (-11% to 86%), and 21% (-44% to 79%), respectively. Bystander lesions (< 2 cm) treated with SRS had a median baseline lesion diameter and volume of 0.5 cm (Range: 0.20-1.64 cm) and 0.06 cc (Range: 0.01-1.94 cc). Corresponding median reductions for SUVmax were 5% at interim and 63% at follow-up scans.

CONCLUSION

This proof-of-concept interim study reports baseline 18F-fluciclovine metrics for patients with brain metastases of varying lesion diameters and volumes. Target lesions appear to demonstrate interval reduction in PET metrics after SSRS, more than dimensional measurements alone.

Multi-institutional competing risks analysis of distant brain failure and salvage patterns after upfront radiosurgery without whole brain radiotherapy for brain metastasis

Background

In this study, we use a competing risks analysis to assess factors predictive of early-salvage whole brain radiotherapy (WBRT) and early death after upfront stereotactic radiosurgery (SRS) alone for brain metastases in an attempt to identify populations that benefit less from upfront SRS.

Patients and methods

Patients from eight academic centers were treated with SRS for brain metastasis. Competing risks analysis was carried out for distant brain failure (DBF) versus death prior to DBF as well as for salvage SRS versus salvage WBRT versus death prior to salvage. Linear regression was used to determine predictors of the number of brain metastases at initial DBF (nDBF).

Results

A total of 2657 patients were treated with upfront SRS alone. Multivariate analysis (MVA) identified an increased hazard of DBF associated with increasing number of brain metastases (P < 0.001), lowest SRS dose received (P < 0.001), and melanoma histology (P < 0.001), while there was a decreased hazard of DBF associated with increasing age (P < 0.001), KPS < 70 (P < 0.001), and progressive systemic disease (P = 0.004). MVA for first salvage SRS versus WBRT versus death prior to salvage revealed an increased hazard of first salvage WBRT seen with increasing number of brain metastases (P < 0.001) and a decreased hazard with widespread systemic disease (P = 0.002) and increasing age (P < 0.001). Variables associated with nDBF included age (P = 0.02), systemic disease status (P = 0.03), melanoma histology (P = 0.05), and initial number of brain metastases (P < 0.001).

Conclusions

Patients with a higher initial number of brain metastases were more likely to experience DBF, have a higher nDBF, and receive early-salvage WBRT, while patients who were older, had lower KPS, or had more systemic disease were more likely to experience death prior to DBF or salvage WBRT.