Technical note: Minimizing CIED artifacts on a 0.35 T MRI-Linac using deep learning.

BACKGROUND: Artifacts from implantable cardioverter defibrillators (ICDs) are a challenge to magnetic resonance imaging (MRI)-guided radiotherapy (MRgRT). PURPOSE: This study tested an unsupervised generative adversarial network to mitigate ICD artifacts in balanced steady-state free precession (bSSFP) cine MRIs and improve image quality and tracking performance for MRgRT. METHODS: Fourteen healthy volunteers (Group A) were scanned on a 0.35 T MRI-Linac with and without an MR conditional ICD taped to their left pectoral to simulate an implanted ICD. bSSFP MRI data from 12 of the volunteers were used to train a CycleGAN model to reduce ICD artifacts. The data from the remaining two volunteers were used for testing. In addition, the dataset was reorganized three times using a Leave-One-Out scheme. Tracking metrics [Dice similarity coefficient (DSC), target registration error (TRE), and 95 percentile Hausdorff distance (95% HD)] were evaluated for whole-heart contours. Image quality metrics [normalized root mean square error (nRMSE), peak signal-to-noise ratio (PSNR), and multiscale structural similarity (MS-SSIM) scores] were evaluated. The technique was also tested qualitatively on three additional ICD datasets (Group B) including a patient with an implanted ICD. RESULTS: For the whole-heart contour with CycleGAN reconstruction: 1) Mean DSC rose from 0.910 to 0.935; 2) Mean TRE dropped from 4.488 to 2.877 mm; and 3) Mean 95% HD dropped from 10.236 to 7.700 mm. For the whole-body slice with CycleGAN reconstruction: 1) Mean nRMSE dropped from 0.644 to 0.420; 2) Mean MS-SSIM rose from 0.779 to 0.819; and 3) Mean PSNR rose from 18.744 to 22.368. The three Group B datasets evaluated qualitatively displayed a reduction in ICD artifacts in the heart. CONCLUSION: CycleGAN-generated reconstructions significantly improved both tracking and image quality metrics when used to mitigate artifacts from ICDs.

Clinical application of a template-guided automated planning routine.

PURPOSE: Determine the dosimetric quality and the planning time reduction when utilizing a template-based automated planning application. METHODS: A software application integrated through the treatment planning system application programing interface, QuickPlan, was developed to facilitate automated planning using configurable templates for contouring, knowledge-based planning structure matching, field design, and algorithm settings. Validations are performed at various levels of the planning procedure and assist in the evaluation of readiness of the CT image, structure set, and plan layout for automated planning. QuickPlan is evaluated dosimetrically against 22 hippocampal-avoidance whole brain radiotherapy patients. The required times to treatment plan generation are compared for the validations set as well as 10 prospective patients whose plans have been automated by QuickPlan. RESULTS: The generations of 22 automated treatment plans are compared against a manual replanning using an identical process, resulting in dosimetric differences of minor clinical significance. The target dose to 2% volume and homogeneity index result in significantly decreased values for automated plans, whereas other dose metric evaluations are nonsignificant. The time to generate the treatment plans is reduced for all automated plans with a median difference of 9' 50″ ± 4' 33″. CONCLUSIONS: Template-based automated planning allows for reduced treatment planning time with consistent optimization structure creation, treatment field creation, plan optimization, and dose calculation with similar dosimetric quality. This process has potential expansion to numerous disease sites.

Phase I/II Trial of Electrophysiology-Guided Noninvasive Cardiac Radioablation for Ventricular Tachycardia.

BACKGROUND: Case studies have suggested the efficacy of catheter-free, electrophysiology-guided noninvasive cardiac radioablation for ventricular tachycardia (VT) using stereotactic body radiation therapy, although prospective data are lacking. METHODS: We conducted a prospective phase I/II trial of noninvasive cardiac radioablation in adults with treatment-refractory episodes of VT or cardiomyopathy related to premature ventricular contractions (PVCs). Arrhythmogenic scar regions were targeted by combining noninvasive anatomic and electric cardiac imaging with a standard stereotactic body radiation therapy workflow followed by delivery of a single fraction of 25 Gy to the target. The primary safety end point was treatment-related serious adverse events in the first 90 days. The primary efficacy end point was any reduction in VT episodes (tracked by indwelling implantable cardioverter defibrillators) or any reduction in PVC burden (as measured by a 24-hour Holter monitor) comparing the 6 months before and after treatment (with a 6-week blanking window after treatment). Health-related quality of life was assessed using the Short Form-36 questionnaire. RESULTS: Nineteen patients were enrolled (17 for VT, 2 for PVC cardiomyopathy). Median noninvasive ablation time was 15.3 minutes (range, 5.4-32.3). In the first 90 days, 2/19 patients (10.5%) developed a treatment-related serious adverse event. The median number of VT episodes was reduced from 119 (range, 4-292) to 3 (range, 0-31; P<0.001). Reduction was observed for both implantable cardioverter defibrillator shocks and antitachycardia pacing. VT episodes or PVC burden were reduced in 17/18 evaluable patients (94%). The frequency of VT episodes or PVC burden was reduced by 75% in 89% of patients. Overall survival was 89% at 6 months and 72% at 12 months. Use of dual antiarrhythmic medications decreased from 59% to 12% ( P=0.008). Quality of life improved in 5 of 9 Short Form-36 domains at 6 months. CONCLUSIONS: Noninvasive electrophysiology-guided cardiac radioablation is associated with markedly reduced ventricular arrhythmia burden with modest short-term risks, reduction in antiarrhythmic drug use, and improvement in quality of life. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov/ . Unique identifier: NCT02919618.

Noninvasive Cardiac Radiation for Ablation of Ventricular Tachycardia.

BACKGROUND: Recent advances have enabled noninvasive mapping of cardiac arrhythmias with electrocardiographic imaging and noninvasive delivery of precise ablative radiation with stereotactic body radiation therapy (SBRT). We combined these techniques to perform catheter-free, electrophysiology-guided, noninvasive cardiac radioablation for ventricular tachycardia. METHODS: We targeted arrhythmogenic scar regions by combining anatomical imaging with noninvasive electrocardiographic imaging during ventricular tachycardia that was induced by means of an implantable cardioverter-defibrillator (ICD). SBRT simulation, planning, and treatments were performed with the use of standard techniques. Patients were treated with a single fraction of 25 Gy while awake. Efficacy was assessed by counting episodes of ventricular tachycardia, as recorded by ICDs. Safety was assessed by means of serial cardiac and thoracic imaging. RESULTS: From April through November 2015, five patients with high-risk, refractory ventricular tachycardia underwent treatment. The mean noninvasive ablation time was 14 minutes (range, 11 to 18). During the 3 months before treatment, the patients had a combined history of 6577 episodes of ventricular tachycardia. During a 6-week postablation "blanking period" (when arrhythmias may occur owing to postablation inflammation), there were 680 episodes of ventricular tachycardia. After the 6-week blanking period, there were 4 episodes of ventricular tachycardia over the next 46 patient-months, for a reduction from baseline of 99.9%. A reduction in episodes of ventricular tachycardia occurred in all five patients. The mean left ventricular ejection fraction did not decrease with treatment. At 3 months, adjacent lung showed opacities consistent with mild inflammatory changes, which had resolved by 1 year. CONCLUSIONS: In five patients with refractory ventricular tachycardia, noninvasive treatment with electrophysiology-guided cardiac radioablation markedly reduced the burden of ventricular tachycardia. (Funded by Barnes-Jewish Hospital Foundation and others.).

Immunotherapy and Radiation Therapy for Non-Small Cell Lung Cancer-A Stimulating Partnership.

Non-small cell lung cancer (NSCLC) is the most common subtype of lung cancer and the leading cause of cancer-related death. Although durable local control rates are high after surgical resection or definitive radiotherapy for early-stage disease, a substantial proportion of these patients eventually experience regional and/or distant failure and succumb to their metastatic disease. The discovery of immunotherapeutics and targeted biologics has revolutionized the treatment of locally advanced and metastatic disease, improving progression-free and overall survival when incorporated with the current standards of care. Notably, post-hoc analyses and early clinical trials provide a growing body of evidence to support a synergistic effect between radiation and immunotherapy for the treatment of NSCLC from early-stage to metastatic disease. Radiotherapy appears to be capable of not only potentiating the effect of immunotherapy in targeted lesions, but also eliciting an antitumor response in distant lesions without any direct exposure to radiation. This review explores the biologic basis of immunotherapy, targeted biologics, and radiotherapy as well as the preclinical and clinical data that support the combined use of radioimmunotherapy for early-stage, locally advanced, and metastatic NSCLC.

Characterization and validation of an intra-fraction motion management system for masked-based radiosurgery.

PURPOSE: Characterize the intra-fraction motion management (IFMM) system found on the Gamma Knife Icon (GKI), including spatial accuracy, latency, temporal performance, and overall effect on delivered dose. METHODS: A phantom was constructed, consisting of a three-axis translation mount, a remote motorized flipper, and a thermoplastic sphere surrounding a radiation detector. An infrared marker was placed on the translation mount secured to the flipper. The spatial accuracy of the IFMM was measured via the translation mount in all Cartesian planes. The detector was centered at the radiation focal point. A remote signal was used to move the marker out of the IFMM tolerance and pause the beam. A two-channel electrometer was used to record the signals from the detector and the flipper when motion was signaled. These signals determined the latency and temporal performance of the GKI. RESULTS: The spatial accuracy of the IFMM was found to be <0.1 mm. The measured latency was <200 ms. The dose difference with five interruptions was <0.5%. CONCLUSION: This work provides a quantitative characterization of the GKI IFMM system as required by the Nuclear Regulatory Commission. This provides a methodology for GKI users to satisfy these requirements using common laboratory equipment in lieu of a commercial solution.

Impact of concurrent chemotherapy with radiation therapy for elderly patients with newly diagnosed glioblastoma: a review of the National Cancer Data Base.

To investigate the utilization and overall survival (OS) impact of concurrent chemotherapy in combination with radiation therapy (RT) for elderly glioblastoma (GBM) patients. Elderly patients (age >70) with supratentorial and nonmetastatic GBM who received RT of 20-75 Gy with concurrent single-agent chemotherapy (ChemoRT) or without (RT alone) during 2004-2012 were identified from the National Cancer Data Base (NCDB). The Cochran-Armitage test was used for trend analysis. Hazard ratios (HR) and 95% confidence intervals (CIs) were determined using Cox proportional hazards. Propensity score analysis was performed to reduce selection bias in treatment allocation. A total of 5252 patients were identified (RT alone: n = 1389; ChemoRT: n = 3863). There was increasing utilization of chemotherapy during this period (45-80%, P < .001). A similar trend was also observed for the subset of age >80 (25-68%, P < .001). ChemoRT was associated with significantly better OS than RT alone (HR 0.79, 95% CI 0.70-0.89, P < .001) on multivariate analysis, and similar OS benefit was demonstrated with 1202 pairs of propensity-matched patients (HR 0.79, 95% CI 0.73-0.86, P < .001). For the matched pair, the median OS was 5.8 months with ChemoRT and 5.0 months with RT alone; the 2-year OS rate was 9% with ChemoRT and 4% with RT alone (P < .001). Concurrent chemotherapy has been administered with RT for the majority of elderly GBM patients. Addition of chemotherapy to RT for elderly GBM patients is associated with significantly improve OS in routine clinical practice.

The Metastatic Spine Disease Multidisciplinary Working Group Algorithms.

The Metastatic Spine Disease Multidisciplinary Working Group consists of medical and radiation oncologists, surgeons, and interventional radiologists from multiple comprehensive cancer centers who have developed evidence- and expert opinion-based algorithms for managing metastatic spine disease. The purpose of these algorithms is to facilitate interdisciplinary referrals by providing physicians with straightforward recommendations regarding the use of available treatment options, including emerging modalities such as stereotactic body radiation therapy and percutaneous tumor ablation. This consensus document details the evidence supporting the Working Group algorithms and includes illustrative cases to demonstrate how the algorithms may be applied.

Inter-fractional portability of deep learning models for lung target tracking on cine imaging acquired in MRI-guided radiotherapy.

MRI-guided radiotherapy systems enable beam gating by tracking the target on planar, two-dimensional cine images acquired during treatment. This study aims to evaluate how deep-learning (DL) models for target tracking that are trained on data from one fraction can be translated to subsequent fractions. Cine images were acquired for six patients treated on an MRI-guided radiotherapy platform (MRIdian, Viewray Inc.) with an onboard 0.35 T MRI scanner. Three DL models (U-net, attention U-net and nested U-net) for target tracking were trained using two training strategies: (1) uniform training using data obtained only from the first fraction with testing performed on data from subsequent fractions and (2) adaptive training in which training was updated each fraction by adding 20 samples from the current fraction with testing performed on the remaining images from that fraction. Tracking performance was compared between algorithms, models and training strategies by evaluating the Dice similarity coefficient (DSC) and 95% Hausdorff Distance (HD95) between automatically generated and manually specified contours. The mean DSC for all six patients in comparing manual contours and contours generated by the onboard algorithm (OBT) were 0.68 ± 0.16. Compared to OBT, the DSC values improved 17.0 - 19.3% for the three DL models with uniform training, and 24.7 - 25.7% for the models based on adaptive training. The HD95 values improved 50.6 - 54.5% for the models based on adaptive training. DL-based techniques achieved better tracking performance than the onboard, registration-based tracking approach. DL-based tracking performance improved when implementing an adaptive strategy that augments training data fraction-by-fraction.

Bintrafusp Alfa With CCRT Followed by Bintrafusp Alfa Versus Placebo With CCRT Followed by Durvalumab in Patients With Unresectable Stage III NSCLC: A Phase 2 Randomized Study.

INTRODUCTION: Preclinical evaluation of bintrafusp alfa (BA) combined with radiotherapy revealed greater antitumor effects than BA or radiotherapy alone. In a phase 1 study, BA exhibited encouraging clinical activity in patients with stage IIIB or IV NSCLC who had received previous treatment. METHODS: This multicenter, double-blind, controlled phase 2 study (NCT03840902) evaluated the safety and efficacy of BA with concurrent chemoradiotherapy (cCRT) followed by BA (BA group) versus placebo with cCRT followed by durvalumab (durvalumab group) in patients with unresectable stage III NSCLC. The primary end point was progression-free survival according to Response Evaluation Criteria in Solid Tumors version 1.1 as assessed by the investigator. On the basis of the recommendation of an independent data monitoring committee, the study was discontinued before the maturity of overall survival data (secondary end point). RESULTS: A total of 153 patients were randomized to either BA (n = 75) or durvalumab groups (n = 78). The median progression-free survival was 12.8 months versus 14.6 months (stratified hazard ratio = 1.48 [95% confidence interval: 0.69-3.17]), in the BA and durvalumab groups, respectively. Trends for overall response rate (29.3% versus 32.1%) and disease control rate (66.7% versus 70.5%) were similar between the two groups. Any-grade treatment-emergent adverse events occurred in 94.6% versus 96.1% of patients in the BA versus durvalumab groups, respectively. Bleeding events in the BA group were mostly grade 1 (21.6%) or 2 (9.5%). CONCLUSIONS: BA with cCRT followed by BA exhibited no efficacy benefit over placebo with cCRT followed by durvalumab in patients with stage III unresectable NSCLC.

Impact of time of day on outcomes after stereotactic radiosurgery for non-small cell lung cancer brain metastases.

BACKGROUND: This study tested the hypothesis that time of day of treatment with stereotactic radiosurgery (SRS) has an effect on local control (LC) and overall survival (OS) in a large cohort of patients with non-small cell lung cancer (NSCLC) brain metastases. METHODS: At Washington University in St. Louis, 437 patients with NSCLC were treated with SRS for NSCLC brain metastases. Receiver operating characteristics analysis was used to identify an optimal cut-point for OS relative to time of day. Kaplan-Meier log-rank statistics, and Cox regression univariate and multivariate analysis were employed to isolate any independent effect of treatment time on OS and LC. Matched-pair analysis was performed to isolate any independent effect of time on OS and LC of day while controlling for confounding variables. RESULTS: Receiver operating characteristics analysis identified a cut-point of 11:41 AM as providing the highest predictive value for OS. On univariate analysis, late SRS was associated with decreased OS, as was age, Karnofsky performance status, risk-stratification schemes, extracranial disease status, and overall burden of brain metastases. On univariate analysis for LC, late SRS was associated with decreased LC, as was burden of brain metastases. On multivariate analysis, only Graded Prognostic Assessment remained predictive of OS, and total number of targets and total tumor volume remained predictive of LC. Matched-pair analysis demonstrated no significant effect of time of day on LC or OS. CONCLUSIONS: Although earlier treatment appears to be associated with improved LC and OS, treatment time fails to remain significant when accounting for confounding variables.

ASTRO Radiation Therapy Summary of the ASCO Guideline on Management of Stage III Non-Small Cell Lung Cancer.

PURPOSE: To develop a radiation therapy summary of recommendations on the management of locally advanced non-small cell lung cancer (NSCLC) based on the Management of Stage III Non-Small Cell Lung Cancer: American Society of Clinical Oncology Guideline, which was endorsed by the American Society for Radiation Oncology (ASTRO). METHODS: The American Society of Clinical Oncology, ASTRO, and the American College of Chest Physicians convened a multidisciplinary panel to develop a guideline based on a systematic review of the literature and a formal consensus process, that has been separately published. A new panel consisting of radiation oncologists from the original guideline as well as additional ASTRO members was formed to provide further guidance to the radiation oncology community. A total of 127 articles met the eligibility criteria to answer 5 clinical questions. This summary focuses on the 3 radiation therapy questions (neoadjuvant, adjuvant, and unresectable settings). RESULTS: Radiation-specific recommendations are summarized with additional relevant commentary on specific questions regarding the management of preoperative radiation, postoperative radiation, and combined chemoradiation. CONCLUSIONS: Patients with stage III NSCLC who are planned for surgical resection, should receive either neoadjuvant chemotherapy or chemoradiation. The addition of neoadjuvant treatment is particularly important in patients planned for surgery in the N2 or superior sulcus settings. Postoperatively, patients who did not receive neoadjuvant chemotherapy should be offered adjuvant chemotherapy. The use of postoperative radiation for completely resected N2 disease is not routinely recommended. Unresectable patients with stage III NSCLC should ideally be managed with combined concurrent chemoradiation using a platinum-based doublet with a standard radiation dose of 60 Gy followed by consolidation durvalumab in patients without progression after initial therapy. Patients who cannot tolerate a concurrent chemoradiation approach can be managed either by sequential chemotherapy followed by radiation or by dose-escalated or hypofractionated radiation alone.

Short-term and long-term effects of noninvasive cardiac radioablation for ventricular tachycardia: A single-center case series.

Background: Noninvasive cardiac radioablation is reported to be effective and safe for the treatment of ventricular tachycardia (VT). Objective: This study aimed to analyze the acute and long-term effects of VT radioablation. Methods: Patients with intractable VT or premature ventricular contraction (PVC)-induced cardiomyopathy were included in this study and treated using a single-fraction 25-Gy dose of cardiac radioablation. To quantitatively analyze the acute response after treatment, continuous electrocardiography monitoring was performed from 24 hours before to 48 hours after irradiation and at the 1-month follow-up. Long-term clinical safety and efficacy were assessed 1-year follow-up. Results: From 2019 to 2020, 6 patients were treated with radioablation for ischemic VT (n = 3), nonischemic VT (n = 2), or PVC-induced cardiomyopathy (n = 1). In the short-term assessment, the total burden of ventricular beats decreased by 49% within 24 hours after radioablation and further decreased by 70% at 1 month. The VT component decreased earlier and more dramatically than the PVC component (decreased by 91% and 57% at 1 month, respectively). In the long-term assessment, 5 patients showed complete (n = 3) or partial (n = 2) remission of ventricular arrhythmias. One patient showed recurrence at 10 months, which was successfully suppressed with medical treatment. The posttreatment PVC coupling interval was prolonged (+38 ms at 1 month). Ischemic VT burden decreased more markedly than nonischemic VT burden after radioablation. Conclusion: In this small case series of 6 patients, without a comparison group, cardiac radioablation appeared to decrease the intractable VT burden. A therapeutic effect was apparent within 1-2 days after treatment but was variable by etiology of cardiomyopathy.

Trends in Stage I Lung Cancer.

INTRODUCTION: The American Cancer Society has recently reported an increase in the percentage of patients with localized lung cancer from 2004 to 2018, coinciding with the initial lung cancer screening guidelines issued in 2013. We conducted a National Cancer Database (NCDB) study to further evaluate the trends in stage I according to patient and tumor characteristics. METHODS: We selected patients with lung cancer from the NCDB Public Benchmark Report diagnosed between 2010 and 2017. Patients with stages I to IV according to the AJCC seventh edition were evaluated according to the year of diagnosis, histology, age, sex, race, and insurance. RESULTS: Among the 1,447,470 patients identified in the database, 56,382 (3.9%) were excluded due to stage 0 or unknown, or incorrect histology, leaving 1,391,088 patients eligible. The percentage of patients with stage I increased from 23.5% in 2010 to 29.1% in 2017 for all lung cancers, from 25.9% to 31.8% in non-small-cell lung cancer (NSCLC), and from 5.0% to 5.4% in small-cell lung cancer (SCLC). Patients younger than 70 years, males and blacks had lower percentages of stage I compared to older patients, females, and nonblacks respectively. Patients with no insurance had the lowest percentage of stage I. CONCLUSIONS: There has been a significant increase in the percentage of stage I lung cancer at diagnosis from 2010 to 2017, which occurred mostly in NSCLC. Although the staging shift was observed in all subsets of patients, there were noticeable imbalances according to demographic factors.

Prospective imaging comparison of anatomic delineation with rapid kV cone beam CT on a novel ring gantry radiotherapy device.

INTRODUCTION: A kV imager coupled to a novel, ring-gantry radiotherapy system offers improved on-board kV-cone-beam computed tomography (CBCT) acquisition time (17-40 seconds) and image quality, which may improve CT radiotherapy image-guidance and enable online adaptive radiotherapy. We evaluated whether inter-observer contour variability over various anatomic structures was non-inferior using a novel ring gantry kV-CBCT (RG-CBCT) imager as compared to diagnostic-quality simulation CT (simCT). MATERIALS/METHODS: Seven patients undergoing radiotherapy were imaged with the RG-CBCT system at breath hold (BH) and/or free breathing (FB) for various disease sites on a prospective imaging study. Anatomy was independently contoured by seven radiation oncologists on: 1. SimCT 2. Standard C-arm kV-CBCT (CA-CBCT), and 3. Novel RG-CBCT at FB and BH. Inter-observer contour variability was evaluated by computing simultaneous truth and performance level estimation (STAPLE) consensus contours, then computing average symmetric surface distance (ASSD) and Dice similarity coefficient (DSC) between individual raters and consensus contours for comparison across image types. RESULTS: Across 7 patients, 18 organs-at-risk (OARs) were evaluated on 27 image sets. Both BH and FB RG-CBCT were non-inferior to simCT for inter-observer delineation variability across all OARs and patients by ASSD analysis (p < 0.001), whereas CA-CBCT was not (p = 0.923). RG-CBCT (FB and BH) also remained non-inferior for abdomen and breast subsites compared to simCT on ASSD analysis (p < 0.025). On DSC comparison, neither RG-CBCT nor CA-CBCT were non-inferior to simCT for all sites (p > 0.025). CONCLUSIONS: Inter-observer ability to delineate OARs using novel RG-CBCT images was non-inferior to simCT by the ASSD criterion but not DSC criterion.

Prospective In Silico Evaluation of Cone-Beam Computed Tomography-Guided StereoTactic Adaptive Radiation Therapy (CT-STAR) for the Ablative Treatment of Ultracentral Thoracic Disease.

Purpose: We conducted a prospective, in silico study to evaluate the feasibility of cone-beam computed tomography (CBCT)-guided stereotactic adaptive radiation therapy (CT-STAR) for the treatment of ultracentral thoracic cancers (NCT04008537). We hypothesized that CT-STAR would reduce dose to organs at risk (OARs) compared with nonadaptive stereotactic body radiation therapy (SBRT) while maintaining adequate tumor coverage. Methods and Materials: Patients who were already receiving radiation therapy for ultracentral thoracic malignancies underwent 5 additional daily CBCTs on the ETHOS system as part of a prospective imaging study. These were used to simulate CT-STAR, in silico. Initial, nonadaptive plans (PI) were created based on simulation images and simulated adaptive plans (PA) were based on study CBCTs. 55 Gy/5 fractions was prescribed, with OAR constraint prioritization over PTV coverage under a strict isotoxicity approach. PI were applied to patients' anatomy of the day and compared with daily PA using dose-volume histogram metrics, with selection of superior plans for simulated delivery. Feasibility was defined as completion of the end-to-end adaptive workflow while meeting strict OAR constraints in ≥80% of fractions. CT-STAR was performed under time pressures to mimic clinical adaptive processes. Results: Seven patients were accrued, 6 with intraparenchymal tumors and 1 with a subcarinal lymph node. CT-STAR was feasible in 34 of 35 simulated fractions. In total, 32 dose constraint violations occurred when the PI was applied to anatomy-of-the-day across 22 of 35 fractions. These violations were resolved by the PA in all but one fraction, in which the proximal bronchial tree dose was still numerically improved through adaptation. The mean difference between the planning target volume and gross total volume V100% in the PI and the PA was -0.24% (-10.40 to 9.90) and -0.62% (-11.00 to 8.00), respectively. Mean end-to-end workflow time was 28.21 minutes (18.02-50.97). Conclusions: CT-STAR widened the dosimetric therapeutic index of ultracentral thorax SBRT compared with nonadaptive SBRT. A phase 1 protocol is underway to evaluate the safety of this paradigm for patients with ultracentral early-stage NSCLC.

Pre-radiotherapy ctDNA liquid biopsy for risk stratification of oligometastatic non-small cell lung cancer.

The optimal treatment for patients with oligometastatic non-small cell lung cancer (NSCLC) remains unclear. Some patients with oligometastatic disease can experience prolonged remission after locally consolidative radiation therapy (RT), while others harbor micrometastatic disease (below current limits of detection by imaging) that may benefit from further prioritization of systemic therapy. To better risk-stratify this population and identify the patients most likely to benefit from locally consolidative radiation therapy, we performed a multi-institutional cohort study of patients with oligometastatic NSCLC undergoing liquid biopsy analysis of circulating tumor DNA (ctDNA). Among this real-world cohort of 1,487 patients undergoing analysis (using the Tempus xF assay), a total of 1,880 ctDNA liquid biopsies along with paired clinical data were obtained across various timepoints. Approximately 20% (n=309) of patients had ctDNA obtained prior to RT and after their diagnosis of oligometastatic disease. Samples were de-identified and analyzed for mutational burden and variant frequencies of detectable deleterious (or likely deleterious) mutations in plasma. Patients with undetectable ctDNA before RT had significantly improved progression-free survival and overall survival compared to patients with detectable ctDNA prior to RT. In patients that received RT, 598 pathogenic (or likely deleterious) variants were identified. ctDNA mutational burden pre-RT and ctDNA maximum variant allele frequency (VAF) pre-RT were both significantly inversely correlated with both progression-free (P = 0.0031 for mutational burden, P = 0.0084 for maximum VAF) and overall survival (P = 0.045 for mutational burden, P = 0.0073 for maximum VAF). Patients without detectable ctDNA prior to RT had significantly improved progression-free survival (P = 0.004) and overall survival (P = 0.03) compared to patients with detectable ctDNA prior to RT. These data suggest that in patients with oligometastatic NSCLC, pre-radiotherapy ctDNA analysis can potentially identify the patients most likely to benefit from locally consolidative RT and experience prolonged progression-free and overall survival. Similarly, ctDNA may be useful to identify those patients with undiagnosed micrometastatic disease, in whom it may be appropriate to prioritize systemic therapy.