BACKGROUND:Magnetic resonance imaging (MRI) provides superior soft tissue contrast compared with CT and is essential for delineation of targets and organs at risk in brain radiotherapy. Because CT is traditionally required for dose calculation in radiation therapy, synthetic CT (sCT) generation from MRI has enabled the development of MR-only workflows. Prior studies have primarily focused on dosimetric equivalence between CT- and sCT-based treatment plans, with limited emphasis on practical implementation challenges encountered during clinical use. PURPOSE:This study aimed to share clinical experience implementing an MR-only brain radiotherapy workflow, with a focus on practical challenges encountered. METHODS:Twenty-eight patients underwent a dedicated MR simulation protocol for sCT generation in addition to standard-of-care planning CT simulation. MRI acquisition was performed using an immobilization mask with a dedicated head coil positioned over the mask. The sCT protocol consisted of four sequences: T1 VIBE Dixon, T2 SPACE, PETRA, and TOF-MRA. Clinical treatment plans generated using the planning CT (pCT) for photon therapy were recalculated on the corresponding sCT datasets. RESULTS:Twenty-eight patients were scanned, and 25 synthetic CT datasets were successfully generated. Nine sCT datasets required rigid re-registration because of inter-sequence patient motion. Findings were categorized into workflow-related sCT challenges, including inter-sequence motion, suboptimal coil placement, and external localization marker interference, and algorithm-related imaging artifacts, including HU misclassification at tissue/bone/air interfaces and sCT degradation in post-operative anatomy with surgical meshes. CONCLUSION:Clinical implementation of a brain MR-only workflow identified two major categories of challenge: workflow-related sCT perturbations and algorithm-related imaging artifacts. This distinction has important implications for mitigation strategies. Case-specific sCT review, structured eligibility screening, and prospective site commissioning are essential for safe clinical deployment. Practical commissioning and per-patient QA checklists are provided as supplementary materials.

Background: Stereotactic body radiation therapy (SBRT) is an emerging modality for the treatment of ventricular tachycardia (VT). The workflow for delineation of the SBRT target is evolving. Objective: This project describes the procedural workflow and outcomes of SBRT for VT. Methods: The primary indication for SBRT was recurrent VT despite maximal contemporary treatment. Target delineation for SBRT involved combining imaging and electrophysiological data. VT burden, defined as the number of sustained VT episodes per month, was compared as the primary outcome. Secondary outcomes assessed included reduction of antitachycardia pacing and defibrillator shock episodes and reduction in the number of antiarrhythmic drugs per patient during follow-up. Results: Workup for VT target delineation and radiation delivery was conducted in 25 patients receiving 27 SBRT procedures. VT management prior to SBRT consideration included ≥2 catheter ablations in 22 (88%) and surgical sympathectomy in 7 patients (28%). Of the 27 performed cases, SBRT target delineation incorporated electrocardiogram of clinical VT in 16 (59%), at least 2 noninvasive imaging modalities to assess scar in 24 (89%), and invasive electroanatomic mapping in 25 (93%). Among 16 patients with a complete 6-month follow-up, the reduction of VT burden per month was 81% (P < .05). Reduction in antitachycardia pacing and defibrillator shocks per month was 86% and 98%, respectively (P < .05). The number of patients on ≥2 antiarrhythmic drugs decreased from 69% to 0% (P < .01). One patient developed diaphragmatic paralysis after SBRT. Conclusion: In patients with recurrent VT despite maximal contemporary antiarrhythmic therapies, SBRT offers a safe alternative once the target is adequately delineated by combining imaging and electrophysiological data.

Purpose/Objective(s)Volumetric Modulated Arc Therapy (VMAT) has become a staple of modern head and neck (HN) radiation planning, but there may exist unexpected failure modes in which VMAT plans are less robust than typically expected. We identify and characterize one such potential instability (to our knowledge not previously described) that can occur at the interface between target volume (e.g. a mucosal primary tumor) and internal air (e.g. pharyngeal lumen, sinuses, nasal cavity, etc.), where the lack of a sufficient region for full dose buildup can lead to development of unexpected hotspots with even minor variations in target geometry.Materials/MethodsPlans for ten HN patients treated with curative-intent VMAT radiation therapy (RT) at our institution in 2023 were reviewed. All patients received 60-69.96 Gy in 30-33 daily fractions with 6MV photons, with plans created in a technology company treatment planning system and calculated with an advanced dose calculation algorithm (version 16.1). To model the effect of swelling or tumor growth at the internal air/tumor interface, verification plans were run in which internal air within 3 mm of the planning target volume (PTV) was overridden to soft tissue density (Hounsfield Unit [HU] = 0), and resulting hotspots were assessed. A modified planning technique was employed to increase robustness, wherein the plan was initially optimized with the luminal air density on CT overridden to HU = -300, before being re-calculated and re-normalized with the original CT HU values. Finally, the modified plan was then assessed for robustness in the event of tissue filling by again overriding luminal air to HU = 0.ResultsAlthough hotspots were well controlled in clinically treated plans at baseline (median 110%, range 109%-114%), relatively minor changes at the tumor-air interface (within 3 mm of PTV) resulted in development of significant unexpected hotspots (median 131%, range 115%-155%). With the proposed robust planning technique, plans were similar at baseline (median hotspot 110%, range 108%-114%, p=0.275 relative to original plan), but significantly more robust in the event of changes at the internal air-tumor interface (median hotspot 110%, range 108%-114%, p=0.001 relative to non-robust plan) while maintaining stable target coverage (D95% of 99.1% to 100.2%).ConclusionIn cases requiring full dose to the interface between target volume and luminal air, standard VMAT plans can exhibit unstable behavior due to insufficient region for dose buildup, resulting in clinically unacceptable hotspots with even minor variations in target geometry—variations that are well under thresholds that would conventionally trigger replanning. A density override planning technique can mitigate this effect, creating VMAT plans that differ minimally at baseline but are substantially more robust against the development of unexpected hotspots. This technique is worthy of further consideration, particularly for HN plans with high dose regions abutting luminal air.

8506 Background: First line therapy options for advanced NSCLC without actionable molecular alterations include immunotherapy (IO) -/+ chemotherapy or chemotherapy alone. NRG-LU002 was a randomized phase II/III study assessing the benefits of local consolidative therapy (LCT) when added to systemic therapy as maintenance in management of oligometastatic NSCLC. Methods: Eligible patients had metastatic NSCLC with 3 or fewer extracranial metastatic sites (excluding primary) exhibiting at least stable disease after 4 cycles of 1 st line systemic therapy. Patients were randomized 1:2 to maintenance systemic therapy or LCT (radiation and/or surgery) followed by maintenance systemic therapy until progression, death, or intolerable toxicity. Stratification factors included histology and IO use. In the randomized phase II (RPhII) portion of the study, the primary endpoint was progression-free survival (PFS) with a planned decision analysis after 216 patients were enrolled and 138 PFS events observed. Secondary endpoints included overall survival (OS), quality of life, and toxicity. The RPhII portion was designed to provide at least 95% power to detect a PFS hazard ratio (HR) of 0.60 at 1-sided significance level of 0.15, and the phase III portion warranted only if the estimated HR was less than 0.83. Results: NRG-LU002 accrual was initiated in 4/2017 and suspended in 11/2021 when the RPhII portion sample size was met. Following the planned interim analysis, the study was closed in 12/2023. Overall, 215 patients (81 -LCT arm, 134 +LCT arm) were enrolled from 68 sites with a median age of 65 years (40-86), 77% white, 95% PS 0/1, 78% non-squamous histology, and 90% having received IO-based systemic therapy. Median follow-up among all/surviving patients were 21.9/29.4 months, respectively. With 138 PFS events from both arms, estimated 1-yr and 2-yr PFS rates were 48% (95% CI: 35.9, 59.0) and 36% (95% CI: 24.8, 47.2) in the maintenance systemic therapy arm and 52% (95% CI: 42.5, 59.8) and 40% (95% CI: 31.5, 48.6) in the LCT + maintenance systemic therapy arm, respectively (2-sided log-rank test p-value = 0.66). Corresponding HR was 0.93 (95% CI: 0.66, 1.31). Of 185 patients treated with IO-containing regimens, the PFS HR was 0.90 (95% CI: 0.61, 1.32). OS HR between two arms was 1.05 (0.70, 1.56) among all patients and 1.05 (0.68, 1.63) among IO-treated patients. For adverse events reported as definitely, probably or possibly related to treatment, there were more LCT + maintenance systemic therapy patients with overall grade 2 or higher toxicities (73% vs 84%) and grade 3 or higher pneumonitis (1% vs 10%). Conclusions: LCT added to IO-based 1 st line systemic therapy was associated with a PFS HR of 0.90. Reducing toxicity and increasing biologically-driven patient selection may optimize this therapeutic ratio. Clinical trial information: NCT03137771 .

Purpose: Significant heterogeneity exists in clinical quality assurance (QA) practices within radiation oncology departments, with most chart rounds lacking prospective peer-reviewed contour evaluation. This has the potential to significantly affect patient outcomes, particularly for head and neck cancers (HNC) given the large variance in target volume delineation. With this understanding, we incorporated a prospective systematic peer contour-review process into our workflow for all patients with HNC. This study aims to assess the effectiveness of implementing prospective peer review into practice for our National Cancer Institute Designated Cancer Center and to report factors associated with contour modifications. Methods and materials: Starting in November 2020, our department adopted a systematic QA process with real-time metrics, in which contours for all patients with HNC treated with radiation therapy were prospectively peer reviewed and graded. Contours were graded with green (unnecessary), yellow (minor), or red (major) colors based on the degree of peer-recommended modifications. Contours from November 2020 through September 2021 were included for analysis. Results: Three hundred sixty contours were included. Contour grades were made up of 89.7% green, 8.9% yellow, and 1.4% red grades. Physicians with >12 months of clinical experience were less likely to have contour changes requested than those with <12 months (8.3% vs 40.9%; P < .001). Contour grades were significantly associated with physician case load, with physicians presenting more than the median number of 50 cases having significantly less modifications requested than those presenting <50 (6.7% vs 13.3%; P = .013). Physicians working with a resident or fellow were less likely to have contour changes requested than those without a trainee (5.2% vs 12.6%; P = .039). Frequency of major modification requests significantly decreased over time after adoption of prospective peer contour review, with no red grades occurring >6 months after adoption. Conclusions: This study highlights the importance of prospective peer contour-review implementation into systematic clinical QA processes for HNC. Physician experience proved to be the highest predictor of approved contours. A growth curve was demonstrated, with major modifications declining after prospective contour review implementation. Even within a high-volume academic practice with subspecialist attendings, >10% of patients had contour changes made as a direct result of prospective peer review. Published by Elsevier Inc. on behalf of American Society for Radiation Oncology.

Purpose: The feasibility of blinding applications for a medical physics residency program has yet to be demonstrated in the literature. We explore the application of an automated approach with human review and intervention to blind applications during the annual medical physics residency review cycle. Methods and Materials: Applications were blinded using an automated process and used for the first phase of residency review in the program. We retrospectively compared self-reported demographic and gender data with blinded and nonblinded cohorts from 2 sequential years of review from a medical physics residency program. Demographic data were analyzed comparing applicants with candidates selected to move to the next phase of the review process. Interrater agreement was also evaluated from the applicant reviewers. Results: We show the feasibility of blinding applications for a medical physics residency program. We observed no more than a 3% difference between the gender selection within the first phase of application review but greater differences when examining race and ethnicity between the 2 methods. The greatest difference was shown to be between Asian and White candidates, where there are statistical differences in the scores in the rubric categories of essay and overall impression. Conclusions: We suggest that each training program critically evaluate its selection criteria for potential sources of bias within the review process. We recommend further critical investigation of processes to promote equity and inclusion to ensure the methods and outcomes are aligned with the mission of the program. Finally, we recommend that the common application provide an option for blinding applications at the source so this can be an option to facilitate efforts for evaluating unconscious bias in the review process.

Purpose/Objective(s) Ventricular arrhythmias (VT and Vfib) account for most sudden cardiac deaths, killing 300,000 per year in the US. Cardiac radioablation (CRA) utilizes SBRT to ablate foci that cannot be otherwise managed with anti-arrhythmics (AAs) or catheter ablation. For radiation oncologists, successfully implementing CRA is difficult as there is little formal training in ventricular anatomy. Herein we report our institution's experience treating 11 patients with refractory VT utilizing the American Heart Association (AHA) 17-segment model of left ventricular anatomy. Materials/Methods Patients were considered for treatment with CRA if they had refractory VT despite AAs and either 1) had undergone unsuccessful catheter ablation(s), or 2) were unable to tolerate catheter ablation for medical/technical reasons. All CRA cases were planned by a multidisciplinary team (MDT) including electrophysiologists (EPs), radiation oncologists, and radiation physicists. The targets were determined by EP based on available diagnostic testing and their locations were defined as including part/all of several segments in the AHA 17-Segment model (patient 7′s target included the right ventricular outflow track, see table). Axial images from 4D CT simulation were reoriented to the cardiac-specific coordinate system employed in AHA 17-segment model, utilizing our published protocol. Targets were delineated by the MDT with appropriate expansions to account for respiratory motion and uncertainty. CRA was delivered with 25 Gy in a single fraction. Follow up included H&P and interrogation of patients' Automatic Implantable Cardioverter Defibrillators (AICDs), which provided data on instances of anti-tachycardia pacing (ATPs), shock therapy and total burden. To assess treatment efficacy, AICD interventions/month were compared prior to and after CRA using the Wilcoxon matched pairs sign rank test. Results Between 1/2020 and 12/2021, 11 patients underwent CRA at our institution, 9 of whom had at least 2 months of follow up before and after treatment as recorded by their AICD (median follow up 12 months and 12 months, respectively). Four patients also underwent cardiac sympathetic denervation prior to CRA. Prior to CRA, median ATP/month, shocks/month, total burden/month were 1.15, 0.56, and 2.31, which significantly decreased to 0.11, 0.00, and 0.11 after CRA (p < 0.05, p < 0.01, p < 0.05, respectively). Except one, all patients had a decrease in ATP and total burden. All 9 patients experienced a decrease in shock burden, and 6 remain shock-free since CRA. In the 11 patients treated, there were no CTCAE grade >1 toxicities that were attributable to CRA. Conclusion In our relatively large singe-institution CRA experience, the AHA 17-segment model has proven to be an effective means of communicating target location, facilitating excellent clinical outcomes with most patients remaining shock-free after treatment.

Background: Ventricular arrhythmias (VAs) are the most lethal arrhythmias. Established therapies to prevent VAs include anti-arrhythmic drugs (AADs) and catheter ablation (CA). For patients with recurrent VAs despite AADs and CA, novel therapies such as cardiac sympathetic denervation (CSD) and stereotactic body radiation therapy (SBRT) exist. This study reports outcomes of CSD and SBRT at a tertiary care academic center. Methods: Study comprises all patients undergoing CSD or SBRT at one center from 10/2018 - 10/2021. Patients with less than 2 months of follow-up were excluded. Retrospective chart review was performed to collate data for demographics, clinical characteristics, arrhythmia burden before and after novel therapies (maximum 12 months), and treatment complications. VA burden in the form of anti-tachycardia pacing (ATP) episodes and defibrillator shocks was assessed as primary efficacy outcome. Treatment complications were assessed as primary safety outcome. Results: Overall, 25 patients underwent novel therapies for VAs, and 13 were excluded for insufficient follow up. Five, 4, and 3 patients underwent CSD, SBRT, and both, respectively. Median age was 66 years (55-72), and 10 (83%) were male. Median left ventricular ejection fraction was 30% (25%-34%). Four patients (33%) had ischemic cardiomyopathy. Median number of AADs and CA prior to novel therapies was 3 (2-5) and 1 (0-2), respectively. Follow up was available for a median of 12 (12-12) months before and 12 (9-12) months after treatment. Overall, VA burden was reduced in 11 of 12 patients (Figure 1). Mean number of ATP and shock episodes was significantly lower after novel therapies (39±43 vs 3±6; p= 0.008). No procedure-related complications were observed. Conclusion: Novel VA treatment modalities are associated with a significantly reduced arrhythmia burden in this single center study. There is a promising role of these therapies as an adjunct to the existing treatment modalities of CA and AADs.

The current clinical interface for Varian's intrafraction motion review (IMR) is limited, providing only qualitative data for review at the treatment console. This study provides a method of extracting and interpreting data from combined log files for quantitative evaluation. Combined log files acquired during patient treatment and a parsing code was developed to scan the combined log file looking for unique identifiers pertaining to the data of interest. We were able to extract clinically relevant parameters from the log files including date and time, gantry angle, expected marker position, found marker position, pixel size, and detection result. This study details how to compare IMR data to Calypso investigating dual-surrogates for intrafraction monitoring during treatment for other researchers to build on these methods. Understanding data recorded during treatment within the combined log files can be helpful in quality improvement of patient care by retrospectively reviewing intrafraction motion.

Background and purpose: The goal of this prospective study is to validate the use of periodic imaging during treatment with a fiducial marker detection algorithm using radiofrequency transponders for prostate cancer patients undergoing treatment for radiation therapy. Materials and methods: Ten male patients were enrolled in this study and treated for prostate cancer with implanted electromagnetic monitoring beacons. We evaluated the accuracy and limitations of Intrafraction Motion Review (IMR) by comparing the known locations of the beacons using the electromagnetic monitoring system to the position data reported from IMR images. Results: A total of 4054 images were taken during treatment. The difference in vector magnitude of the two methods is centered around zero (mean: 0.03 cm, SD: 0.16 cm) and Lin's Concordance Correlation Coefficient (CCC) is 0.99 (95% CI: 0.98, 1) overall. The Euclidean distance between the two methods was close to zero (median: 0.09 cm, IQR: 0.06, 0.14 cm). The difference in distance between any two markers was centered around zero (mean: 0.01 cm, SD: 0.12 cm) and Lin's CCC is 0.97 (95% CI: 0.96, 0.98) overall. Conclusion: The accuracy of the algorithm for detected markers within the 2D images is comparable to electromagnetic monitoring for fiducial identification when detected. IMR could provide an alternate solution for patients with contraindications of use of an electromagnetic monitoring system and a cost effective alternative to the acquisition of an additional system for patient monitoring, but does not provide data for pre-treatment set-up verification and real-time 3D positioning during treatment. Published by Elsevier B.V.

Hypofractionation can be beneficial for patients with prostate cancer, but higher dose per fraction with reduced margins can be difficult to achieve due to intrafraction motion. The goal of this prospective study is to validate the use of periodic imaging during treatment with fiducial marker detection algorithm by using radiofrequency transponders for prostate cancer patients undergoing treatment for radiation therapy. Kilovoltage (kV) imaging collected during radiotherapy treatment automatically detect fiducial markers from images and compares their real-time location to their expected location from the treatment plan. This information is useful clinically to pause the treatment beam if the region of interest has moved during the course of treatment. We are currently accruing male patients treated for prostate cancer with three implanted beacons emitting a radiofrequency. Ten (10) patients are being accrued for the study and data is collected for five (5) treatment sessions for each patient. Periodic imaging during treatment with fiducial marker detection algorithm was used to collect kV images during the patient treatment. Since the treatment plans are arc-based, an image was collected every 10 degrees of gantry rotation. A typical prostate treatment plan involves two full treatment arcs for approximately 72 images per fraction. The position data from the periodic imaging during treatment with fiducial marker detection algorithm was compared to the positions from the data from the radiofrequency beacons projected on KV detector plane to evaluate the positional accuracy of the system. We present the preliminary data from the first five patients which include data reported from beacons detected within a 5 mm threshold (N = 4335). The analysis of the data using a two-sample t-test fail to reject the null hypothesis at 0.05 significance level (P = 0.714) meaning that the detected marker locations are the same. The difference between the two technologies was found to be 0 ± 1.4 mm in the x-direction and 0.5 ± 1.8 mm in the y-direction. The commercially available fiducial marker detection algorithm allows imaging during treatment to automatically detect fiducial markers and compare their real-time location to their expected location from the treatment plan based on kV images. Determination of fiducial marker location between periodic imaging during treatment with fiducial marker detection algorithm could provide a cost-effective alternative to an additional real-time tracking and positioning system. This technology can provide an alternate solution to patients with contraindications to the use or implantation of beacons emitting a radiofrequency.