Surgically targeted radiation therapy versus stereotactic radiation therapy: A dosimetric comparison for brain metastasis resection cavities.

PURPOSE: Surgically targeted radiation therapy (STaRT) with Cesium-131 seeds embedded in a collagen tile is a promising treatment for recurrent brain metastasis. In this study, the biological effective doses (BED) for normal and target tissues from STaRT plans were compared with those of external beam radiotherapy (EBRT) modalities. METHODS: Nine patients (n = 9) with 12 resection cavities (RCs) who underwent STaRT (cumulative physical dose of 60 Gy to a depth of 5 mm from the RC edge) were replanned with CyberKnifeⓇ (CK), Gamma KnifeⓇ (GK), and intensity modulated proton therapy (IMPT) using an SRT approach (30 Gy in 5 fractions). Statistical significance comparing D95% and D90% in BED10Gy (BED10Gy95% and BED10Gy90%) and to RC + 0 to + 5 mm expansion margins, and parameters associated with radiation necrosis risk (V83Gy, V103Gy, V123Gy and V243Gy) to the normal brain were evaluated by a Wilcoxon-signed rank test. RESULTS: For RC + 0 mm, median BED10Gy 90% for STaRT (90.1 Gy10, range: 64.1-140.9 Gy10) was significantly higher than CK (74.3 Gy10, range:59.3-80.4 Gy10, p = 0.04), GK (69.4 Gy10, range: 59.8-77.1 Gy10, p = 0.005), and IMPT (49.3 Gy10, range: 49.0-49.7 Gy10, p = 0.003), respectively. However, for the RC + 5 mm, the median BED10Gy 90% for STaRT (34.1 Gy10, range: 22.2-59.7 Gy10) was significantly lower than CK (44.3 Gy10, range: 37.8-52.4 Gy10), and IMPT (46.6 Gy10, range: 45.1-48.5 Gy10), respectively, but not significantly different from GK (34.1 Gy10, range: 22.8-47.0 Gy10). The median V243Gy was significantly higher in CK (11.7 cc, range: 4.7-20.1 cc), GK(6.2 cc, range: 2.3-11.9 cc) and IMPT (19.9 cc, range: 11.1-36.6 cc) compared to STaRT (1.1 cc, range: 0.0-7.8 cc) (p < 0.01). CONCLUSIONS: This comparative analysis suggests a STaRT approach may treat recurrent brain tumors effectively via delivery of higher radiation doses with equivalent or greater BED up to at least 3 mm from the RC edge as compared to EBRT approaches.

Patient-specific quality assurance of dynamically-collimated proton therapy treatment plans.

BACKGROUND: The dynamic collimation system (DCS) provides energy layer-specific collimation for pencil beam scanning (PBS) proton therapy using two pairs of orthogonal nickel trimmer blades. While excellent measurement-to-calculation agreement has been demonstrated for simple cube-shaped DCS-trimmed dose distributions, no comparison of measurement and dose calculation has been made for patient-specific treatment plans. PURPOSE: To validate a patient-specific quality assurance (PSQA) process for DCS-trimmed PBS treatment plans and evaluate the agreement between measured and calculated dose distributions. METHODS: Three intracranial patient cases were considered. Standard uncollimated PBS and DCS-collimated treatment plans were generated for each patient using the Astroid treatment planning system (TPS). Plans were recalculated in a water phantom and delivered at the Miami Cancer Institute (MCI) using an Ion Beam Applications (IBA) dedicated nozzle system and prototype DCS. Planar dose measurements were acquired at two depths within low-gradient regions of the target volume using an IBA MatriXX ion chamber array. RESULTS: Measured and calculated dose distributions were compared using 2D gamma analysis with 3%/3 mm criteria and low dose threshold of 10% of the maximum dose. Median gamma pass rates across all plans and measurement depths were 99.0% (PBS) and 98.3% (DCS), with a minimum gamma pass rate of 88.5% (PBS) and 91.2% (DCS). CONCLUSIONS: The PSQA process has been validated and experimentally verified for DCS-collimated PBS. Dosimetric agreement between the measured and calculated doses was demonstrated to be similar for DCS-collimated PBS to that achievable with noncollimated PBS.

Stereotactic Body Radiation Therapy Versus Conventional Radiation Therapy for Painful Spinal Metastases: A Comparative Analysis of Randomized Trials and Practical Considerations.

PURPOSE: Recent randomized trials have compared the efficacy and safety of stereotactic body radiation therapy (SBRT) with those of standard conventional external beam radiation therapy (cEBRT) for the treatment of painful spinal metastases. We conducted a composite analysis of these trials in order to inform current practice using pooled outcomes. METHODS AND MATERIALS: Data from each randomized trial were abstracted from the final publications with biologically effective doses (BEDs) recalculated for SBRT and cEBRT. Primary outcome measures were overall pain response (OR) and complete pain response (CR) rates at 1, 3, and 6 months and rates of vertebral compression fracture. Random effects models were used to estimate primary outcome measures, and meta-regression assessed the effect of BED. RESULTS: Four prospective randomized clinical trials published between 2018 and 2024 were included, with a total of 686 patients (383 and 303 in the SBRT and cEBRT groups, respectively). Dose and fraction (fx) number ranged from 24 Gy/1 fx to 48.5 Gy/10 fx for the SBRT group (median BED using an α-to-ß ratio of 10, 50 Gy) and from 8 Gy/1 fx to 30 Gy/10 fx for the cEBRT group (median BED using an α-to-ß ratio of 10, 28 Gy). The 1-, 3-, and 6-month OR rates for SBRT and cEBRT were similar: 53.6%, 52.4%, and 58.8% versus 48.4%, 47.9%, and 43.8%, respectively (p > .05). The 3-month CR rate was significantly higher for SBRT than for cEBRT (31.9% vs 14.8%; risk ratio, 2.26; 95% CI, 1.48-3.45; p < .001), but not the 6-month rate (34.4% vs 16.3%; risk ratio, 1.83; 95% CI, 0.74-4.53; p = .194). Vertebral compression fracture rates were similar at 17.3% and 18.4% for SBRT and cEBRT, respectively. No significant dose-dependent effect was observed with increasing BED for any efficacy or safety outcomes. CONCLUSIONS: OR rates are similar, but CR rates appear higher with SBRT than with cEBRT, yet no dose-dependent effects were identified despite approximately 1.8 × BED dose with SBRT.

Case report: Intrafraction dose-guided tracking for gastrointestinal organ-at-risk isotoxicity delivery on an MR-guided radiotherapy system.

In the current era of high-precision radiation therapy, real-time magnetic resonance (MR)-guided tracking of the tumor and organs at risk (OARs) is a novel approach that enables accurate and safe delivery of high-dose radiation. Organ tracking provides a general sense of the need for daily online adaptation but lacks precise information regarding exact dosimetry. To overcome this limitation, we developed the methodology for monitoring intrafraction motion with real-time MR-guided isodose line-based tracking of an OAR in combination with anatomic tumor-based tracking and reported the first case treated with this approach. An isolated para-aortic (PA) nodal recurrence from carcinosarcoma of the endometrium was treated with an ablative dose of 50 Gy in five fractions using MR-guided radiotherapy (MRgRT). This report demonstrates the feasibility, workflow, dosimetric constraints, and treatment paradigm for real-time isodose line-based OAR tracking and gating to enable an isotoxicity delivery approach. This innovative treatment strategy effectively tracked the intrafraction motion of both the target and OAR independently and enhanced the accuracy of structure localization in time and space with a more precise dosimetric evaluation.

Establishing Updated Safety Standards for Independent 99mTc-MAA SPECT/CT Treatment Planning in Radioembolization.

PURPOSE: Significant improvements within radioembolization imaging and dosimetry permit the development of an accurate and personalized pretreatment plan using technetium 99m-labeled macroaggregated albumin (99mTc-MAA) and single-photon emission computed tomography (SPECT) combined with anatomical CT (SPECT/CT). Despite these potential advantages, the clinical transition to pretreatment protocols with SPECT/CT is hindered by their unknown safety constraints. This study aimed to address this issue by establishing novel dose limits for 99mTc-MAA SPECT/CT to enable quantitative pretreatment planning. METHODS AND MATERIALS: Stratification criteria to determine images most viable for dosimetry analysis were created from a cohort of 85 patients. SPECT/CT, cone beam CT, and activity calculations derived from the local deposition method were used to create an accurate pretreatment protocol. Planar and SPECT/CT images were compared using linear regression and modified Bland-Altman analyses to convert accepted planar dose limits to SPECT/CT. To validate these new dose limits, activity calculations based on SPECT/CT were compared with those calculated with the body surface area and planar methods for three treatment plans. RESULTS: A total of 38 of 85 patients were deemed viable for dosimetry analysis. SPECT yielded greater lung shunt fractions (LSFs) than planar imaging when LSFs were <4.89%, whereas SPECT yielded lower LSFs than planar imaging when LSFs were >4.89%. Planar to SPECT/CT dose conversions were 0.76×, 0.70×, and 0.55× for the whole liver, normal liver, and lungs, respectively. Patients with SPECT LSFs ≤4.89% were safely treated with the direct application of planar lung dose limits. Activity calculations with the newly established SPECT/CT dose limits were greater than those of the body surface area method by a median range of 33.1% to 61.9% and were lower than planar-based activity calculations by a median range of 12.5% to 13.7% for the whole liver and by 29.4% to 32.2% for the normal liver. CONCLUSIONS: This study demonstrated a safe method for translating dose limits from 99mTc-MAA planar imaging to SPECT/CT. A robust pretreatment protocol was further developed guided by the current knowledge in the field. Established SPECT/CT dose limits safely treated 97.5% of patients and permitted the application of independent pretreatment planning with 99mTc-MAA SPECT/CT.

Comparative evaluation of outcomes amongst different radiosurgery management paradigms for patients with large brain metastasis.

INTRODUCTION: This study compares four management paradigms for large brain metastasis (LMB): fractionated SRS (FSRS), staged SRS (SSRS), resection and postoperative-FSRS (postop-FSRS) or preoperative-SRS (preop-SRS). METHODS: Patients with LBM (≥ 2 cm) between July 2017 and January 2022 at a single tertiary institution were evaluated. Primary endpoints were local failure (LF), radiation necrosis (RN), leptomeningeal disease (LMD), a composite of these variables, and distant intracranial failure (DIF). Gray's test compared cumulative incidence, treating death as a competing risk with a random survival forests (RSF) machine-learning model also used to evaluate the data. RESULTS: 183 patients were treated to 234 LBMs: 31.6% for postop-FSRS, 28.2% for SSRS, 20.1% for FSRS, and 20.1% for preop-SRS. The overall 1-year composite endpoint rates were comparable (21 vs 20%) between nonoperative and operative strategies, but 1-year RN rate was 8 vs 4% (p = 0.012), 1-year overall survival (OS) was 48 vs. 69% (p = 0.001), and 1-year LMD rate was 5 vs 10% (p = 0.052). There were differences in the 1-year RN rates (7% FSRS, 3% postop-FSRS, 5% preop-SRS, 10% SSRS, p = 0.037). With RSF analysis, the out-of-bag error rate for the composite endpoint was 47%, with identified top-risk factors including widespread extracranial disease, > 5 total lesions, and breast cancer histology. CONCLUSION: This is the first study to conduct a head-to-head retrospective comparison of four SRS methods, addressing the lack of randomized data in LBM literature amongst treatment paradigms. Despite patient characteristic trends, no significant differences were found in LF, composite endpoint, and DIF rates between non-operative and operative approaches.

Quality assurance of an established online adaptive radiotherapy program: patch and software upgrade.

Introduction: The ability to dynamically adjust target contours, derived Boolean structures, and ultimately, the optimized fluence is the end goal of online adaptive radiotherapy (ART). The purpose of this work is to describe the necessary tests to perform after a software patch installation and/or upgrade for an established online ART program. Methods: A patch upgrade on a low-field MR Linac system was evaluated for post-software upgrade quality assurance (QA) with current infrastructure of ART workflow on (1) the treatment planning system (TPS) during the initial planning stage and (2) the treatment delivery system (TDS), which is a TPS integrated into the delivery console for online ART planning. Online ART QA procedures recommended for post-software upgrade include: (1) user interface (UI) configuration; (2) TPS beam model consistency; (3) segmentation consistency; (4) dose calculation consistency; (5) optimizer robustness consistency; (6) CT density table consistency; and (7) end-to-end absolute ART dose and predicted dose measured including interruption testing. Differences of calculated doses were evaluated through DVH and/or 3D gamma comparisons. The measured dose was assessed using an MR-compatible A26 ionization chamber in a motion phantom. Segmentation differences were assessed through absolute volume and visual inspection. Results: (1) No UI configuration discrepancies were observed. (2) Dose differences on TPS pre-/post-software upgrade were within 1% for DVH metrics. (3) Differences in segmentation when observed were small in general, with the largest change noted for small-volume regions of interest (ROIs) due to partial volume impact. (4) Agreement between TPS and TDS calculated doses was 99.9% using a 2%/2-mm gamma criteria. (5) Comparison between TPS and online ART plans for a given patient plan showed agreement within 2% for targets and 0.6 cc for organs at risk. (6) Relative electron densities demonstrated comparable agreement between TPS and TDS. (7) ART absolute and predicted measured end-to-end doses were within 1% of calculated TDS. Discussion: An online ART QA program for post-software upgrade has been developed and implemented on an MR Linac system. Testing mechanics and their respective baselines may vary across institutions, but all necessary components for a post-software upgrade QA have been outlined and detailed. These outlined tests were demonstrated feasible for a low-field MR Linac system; however, the scope of this work may be applied and adapted more broadly to other online ART platforms.

Clinical application of an institutional fractionated stereotactic radiosurgery (FSRS) program for brain metastases delivered with MRIdianⓇ BrainTx™.

Single-fraction stereotactic radiosurgery (SRS) or fractionated SRS (FSRS) are well established strategies for patients with limited brain metastases. A broad spectrum of modern dedicated platforms are currently available for delivering intracranial SRS/FSRS; however, SRS/FSRS delivered using traditional CT-based platforms relies on the need for diagnostic MR images to be coregistered to planning CT scans for target volume delineation. Additionally, the on-board image guidance on traditional platforms yields limited inter-fraction and intra-fraction real-time visualization of the tumor at the time of treatment delivery. MR Linacs are capable of obtaining treatment planning MR and on-table MR sequences to enable visualization of the targets and organs-at-risk and may subsequently help identify anatomical changes prior to treatment that may invoke the need for on table treatment adaptation. Recently, an MR-guided intracranial package (MRIdian A3i BrainTxTM) was released for intracranial treatment with the ability to perform high-resolution MR sequences using a dedicated brain coil and cranial immobilization system. The objective of this report is to provide, through the experience of our first patient treated, a comprehensive overview of the clinical application of our institutional program for FSRS adaptive delivery using MRIdian's A3i BrainTx system-highlights include reviewing the imaging sequence selection, workflow demonstration, and details in its delivery feasibility in clinical practice, and dosimetric outcomes.

Accelerated Hypofractionated Magnetic Resonance Guided Adaptive Radiation Therapy for Ultracentral Lung Tumors.

Radiotherapy for ultracentral lung tumors represents a treatment challenge, considering the high rates of high-grade treatment-related toxicities with stereotactic body radiation therapy (SBRT) or hypofractionated schedules. Accelerated hypofractionated magnetic resonance-guided adaptive radiation therapy (MRgART) emerged as a potential game-changer for tumors in these challenging locations, in close proximity to central organs at risk, such as the trachea, proximal bronchial tree, and esophagus. In this series, 13 consecutive patients, predominantly male (n = 9), with a median age of 71 (range (R): 46-85), underwent 195 MRgART fractions (all 60 Gy in 15 fractions) to metastatic (n = 12) or primary ultra-central lung tumors (n = 1). The median gross tumor volumes (GTVs) and planning target volumes (PTVs) were 20.72 cc (R: 0.54-121.65 cc) and 61.53 cc (R: 3.87-211.81 cc), respectively. The median beam-on time per fraction was 14 min. Adapted treatment plans were generated for all fractions, and indications included GTV/PTV undercoverage, OARs exceeding tolerance doses, or both indications in 46%, 18%, and 36% of fractions, respectively. Eight patients received concurrent systemic therapies, including immunotherapy (four), chemotherapy (two), and targeted therapy (two). The crude in-field loco-regional control rate was 92.3%. No CTCAE grade 3+ toxicities were observed. Our results offer promising insights, suggesting that MRgART has the potential to mitigate toxicities, enhance treatment precision, and improve overall patient care in the context of ultracentral lung tumors.

Commissioning Intracranial Stereotactic Radiosurgery for a Magnetic Resonance-Guided Radiation Therapy (MRgRT) System: MR-RT Localization and Dosimetric End-to-End Validation.

PURPOSE: This is the first reporting of the MRIdian A3iTM intracranial package (BrainTxTM) and benchmarks the end-to-end localization and dosimetric accuracy for commissioning an magnetic resonace (MR)-guided stereotactic radiosurgery program. We characterized the localization accuracy between MR and radiation (RT) isocenter through an end-to-end hidden target test, relative dose profile intercomparison, and absolute dose validation. METHODS AND MATERIALS: BrainTx consists of a dedicated head coil, integrated mask immobilization system, and high-resolution MR sequences. Coil and baseplate attenuation was quantified. An in-house phantom (Cranial phantOm foR magNetic rEsonance Localization of a stereotactIc radiosUrgery doSimeter, CORNELIUS) was developed from a mannequin head filled with silicone gel, film, and MR BB with pinprick. A hidden target test evaluated MR-RT localization of the 1×1×1 mm3 TrueFISP MR and relative dose accuracy in film for a 1 cm diameter (International Electrotechnical Commission (IEC)-X/IEC-Y) and 1.5 cm diameter (IEC-Y/IEC-Z) spherical target. Two clinical cases (irregular-shaped target and target abutting brainstem) were mapped to the CORNELIUS phantom for feasibility assessment. A 2-dimensional (2D)-gamma compared calculated and measured dose for spherical and clinical targets with 1 mm/1% and 2 mm/2% criteria, respectively. A small-field chamber (A26MR) measured end-to-end absolute dose for a 1 cm diameter target. RESULTS: Coil and baseplate attenuation were 0.7% and 2.7%, respectively. The displacement of MR to RT localization as defined through the pinprick was 0.49 mm (IEC-X), 0.27 mm (IEC-Y), and 0.51 mm (IEC-Z) (root mean square 0.76 mm). The reproducibility across IEC-Y demonstrated high fidelity (<0.02 mm). Gamma pass rates were 97.1% and 95.4% for 1 cm and 1.5 cm targets, respectively. Dose profiles for an irregular-shaped target and abutting organ-at-risk-target demonstrated pass rates of 99.0% and 92.9%, respectively. The absolute end-to-end dose difference was <1%. CONCLUSIONS: All localization and dosimetric evaluation demonstrated submillimeter accuracy, per the TG-142, TG-101, MPPG 9.a. criteria for SRS/SRT systems, indicating acceptable delivery capabilities with a 1 mm setup margin.

Dosimetric comparison of magnetic resonance-guided radiation therapy, intensity-modulated proton therapy and volumetric-modulated arc therapy for distal esophageal cancer.

Advances in radiotherapy (RT) technologies permit significant decreases in the dose delivered to organs at risk (OARs) for patients with esophageal cancer (EC). Novel RT modalities such as proton beam therapy (PBT) and magnetic resonance-guided radiotherapy (MRgRT), as well as motion management techniques including breath hold (BH) are expected to further improve the therapeutic ratio. However, to our knowledge, the dosimetric benefits of PBT vs MRgRT vs volumetric-modulated arc therapy (VMAT) have not been directly compared for EC. We performed a retrospective in silico evaluation using the images and datasets of nine distal EC patients who were treated at our institution with a 0.35-Tesla MR linac to 50.4 Gy in 28 fractions in mid-inspiration BH (BH-MRgRT). Comparison free-breathing (FB) intensity-modulated PBT (FB-IMPT) and FB-VMAT plans were retrospectively created using the same prescription dose, target volume coverage goals, and OAR constraints. A 5 mm setup margin was used for all plans. BH-IMPT and BH-VMAT plans were not evaluated as they would not reflect our institutional practice. Planners were blinded to the results of the treatment plans created using different radiation modalities. The primary objective was to compare plan quality, target volume coverage, and OAR doses. All treatment plans met pre-defined target volume coverage and OAR constraints. The median conformity and homogeneity indices between FB-IMPT, BH-MRgRT and FB-VMAT were 1.13, 1.25, and 1.43 (PITV) and 1.04, 1.15, 1.04 (HI), respectively. For FB-IMPT, BH-MRgRT and FB-VMAT the median heart dose metrics were 52.8, 79.3, 146.8 (V30Gy, cc), 35.5, 43.8, 77.5 (V40Gy, cc), 16.9, 16.9, 32.5 (V50Gy, cc) and 6.5, 14.9, 17.3 (mean, Gy), respectively. Lung dose metrics were 8.6, 7.9, 18.5 (V20Gy, %), and 4.3, 6.3, 11.2 (mean, Gy), respectively. The mean liver dose (Gy) was 6.5, 19.6, 22.2 respectively. Both FB-IMPT and BH-MRgRT achieve substantial reductions in heart, lung, and liver dose compared to FB-VMAT. We plan to evaluate dosimetric outcomes across these RT modalities assuming consistent use of BH.

Integration and dosimetric validation of a dynamic collimation system for pencil beam scanning proton therapy.

Objective.To integrate a Dynamic Collimation System (DCS) into a pencil beam scanning (PBS) proton therapy system and validate its dosimetric impact.Approach.Uncollimated and collimated treatment fields were developed for clinically relevant targets using an in-house treatment plan optimizer and an experimentally validated Monte Carlo model of the DCS and IBA dedicated nozzle (DN) system. The dose reduction induced by the DCS was quantified by calculating the mean dose in 10- and 30-mm two-dimensional rinds surrounding the target. A select number of plans were then used to experimentally validate the mechanical integration of the DCS and beam scanning controller system through measurements with the MatriXX-PT ionization chamber array and EBT3 film. Absolute doses were verified at the central axis at various depths using the IBA MatriXX-PT and PPC05 ionization chamber.Main results.Simulations demonstrated a maximum mean dose reduction of 12% for the 10 mm rind region and 45% for the 30 mm rind region when utilizing the DCS. Excellent agreement was observed between Monte Carlo simulations, EBT3 film, and MatriXX-PT measurements, with gamma pass rates exceeding 94.9% for all tested plans at the 3%/2 mm criterion. Absolute central axis doses showed an average verification difference of 1.4% between Monte Carlo and MatriXX-PT/PPC05 measurements.Significance.We have successfully dosimetrically validated the delivery of dynamically collimated proton therapy for clinically relevant delivery patterns and dose distributions with the DCS. Monte Carlo simulations were employed to assess dose reductions and treatment planning considerations associated with the DCS.

Online adaptive radiotherapy: Assessment of planning technique and its impact on longitudinal plan quality robustness in pancreatic cancer.

BACKGROUND AND PURPOSE: Planning on a static dataset that reflects the simulation day anatomy is routine for SBRT. We hypothesize the quality of on-table adaptive plans is similar to the baseline plan when delivering stereotactic MR-guided adaptive radiotherapy (SMART) for pancreatic cancer (PCa). MATERIALS AND METHODS: Sixty-seven inoperable PCa patients were prescribed 50 Gy/5-fraction SMART. Baseline planning included: 3-5 mm gastrointestinal (GI) PRV, 50 Gy optimization target (PTVopt) based on GI PRV, conformality rings, and contracted GTV to guide the hotspot. For each adaptation, GI anatomy was re-contoured, followed by re-optimization. Plan quality was evaluated for target coverage (TC = PTVopt V100%/volume), PTV D90% and D80%, homogeneity index (HI = PTVopt D2%/D98%), prescription isodose/target volume (PITV), low-dose conformity (D2cm = maximum dose at 2 cm from PTVopt/Rx dose), and gradient index (R50%=50% Rx isodose volume/PTVopt volume).A novel global planning metric, termed the Pancreas Adaptive Radiotherapy Score (PARTS), was developed and implemented based on GI OAR sparing, PTV/GTV coverage, and conformality. Adaptive robustness (baseline to fraction 1) and stability (difference between two fractions with highest GI PRV variation) were quantified. RESULTS: OAR constraints were met on all baseline (n = 67) and adaptive (n = 318) plans. Coverage for baseline/adaptive plans was mean ± SD at 44.9 ± 5.8 Gy/44.3 ± 5.5 Gy (PTV D80%), 50.1 ± 4.2 Gy/49.1 ± 4.7 Gy (PTVopt D80%), and 80%±18%/74%±18% (TC), respectively. Mean homogeneity and conformality for baseline/adaptive plans were 0.87 ± 0.25/0.81 ± 0.30 (PITV), 3.81 ± 1.87/3.87 ± 2.0 (R50%), 1.53 ± 0.23/1.55 ± 0.23 (HI), and 58%±7%/59%±7% (D2cm), respectively. PARTS was found to be a sensitive metric due to its additive influence of geometry changes on PARTS' sub-metrics. There were no statistical differences (p > 0.05) for stability, except for PARTS (p = 0.04, median difference -0.6%). Statistical differences for robustness when significant were small for most metrics (<2.0% median). Median adaptive re-optimizations were 2. CONCLUSION: We describe a 5-fraction ablative SMART planning approach for PCa that is robust and stable during on-table adaption, due to gradients controlled by a GI PRV technique and the use of rings. These findings are noteworthy given that daily interfraction anatomic GI OAR differences are routine, thus necessitating on-table adaptation. This work supports feasibility towards utilizing a patient-independent, template on-table adaptive approach.

Surgically targeted radiation therapy (STaRT) for recurrent brain metastases: Initial clinical experience.

PURPOSE: This study evaluates the outcomes of recurrent brain metastasis treated with resection and brachytherapy using a novel Cesium-131 carrier, termed surgically targeted radiation therapy (STaRT), and compares them to the first course of external beam radiotherapy (EBRT). METHODS: Consecutive patients who underwent STaRT between August 2020 and June 2022 were included. All patients underwent maximal safe resection with pathologic confirmation of viable disease prior to STaRT to 60 Gy to a 5-mm depth from the surface of the resection cavity. Complications were assessed using CTCAE version 5.0. RESULTS: Ten patients with 12 recurrent brain metastases after EBRT (median 15.5 months, range: 4.9-44.7) met the inclusion criteria. The median BED10Gy90% and 95% were 132.2 Gy (113.9-265.1 Gy) and 116.0 Gy (96.8-250.6 Gy), respectively. The median maximum point dose BED10Gy for the target was 1076.0 Gy (range: 120.7-1478.3 Gy). The 6-month and 1-year local control rates were 66.7% and 33.3% for the prior EBRT course; these rates were 100% and 100% for STaRT, respectively (p < 0.001). At a median follow-up of 14.5 months, there was one instance of grade two radiation necrosis. Surgery-attributed complications were observed in two patients including pseudomeningocele and minor headache. CONCLUSIONS: STaRT with Cs-131 presents an alternative approach for operable recurrent brain metastases and was associated with superior local control than the first course of EBRT in this series. Our initial clinical experience shows that STaRT is associated with a high local control rate, modest surgical complication rate, and low radiation necrosis risk in the reirradiation setting.

A study on inter-planner plan quality variability using a manual planning- or Lightning dose optimizer-approach for single brain lesions treated with the Gamma Knife® Icon™.

PURPOSE: The purpose of this study is to investigate inter-planner plan quality variability using a manual forward planning (MFP)- or fast inverse planning (FIP, Lightning)-approach for single brain lesions treated with the Gamma Knife® (GK) Icon™. METHODS: Thirty patients who were previously treated with GK stereotactic radiosurgery or radiotherapy were selected and divided into three groups (post-operative resection cavity, intact brain metastasis, and vestibular schwannoma [10 patients per group]). Clinical plans for the 30 patients were generated by multiple planners using FIP only (1), a combination of FIP and MFP (12), and MFP only (17). Three planners (Senior, Junior, and Novice) with varying experience levels re-planned the 30 patients using MFP and FIP (two plans per patient) with planning time limit of 60 min. Statistical analysis was performed to compare plan quality metrics (Paddick conformity index, gradient index, number of shots, prescription isodose line, target coverage, beam-on-time (BOT), and organs-at-risk doses) of MFP or FIP plans among three planners and to compare plan quality metrics between each planner's MFP/FIP plans and clinical plans. Variability in FIP parameter settings (BOT, low dose, and target max dose) and in planning time among the planners was also evaluated. RESULTS: Variations in plan quality metrics of FIP plans among three planners were smaller than those of MFP plans for all three groups. Junior's MFP plans were the most comparable to the clinical plans, whereas Senior's and Novice's MFP plans were superior and inferior, respectively. All three planners' FIP plans were comparable or superior to the clinical plans. Differences in FIP parameter settings among the planners were observed. Planning time was shorter and variations in planning time among the planners were smaller for FIP plans in all three groups. CONCLUSIONS: The FIP approach is less planner dependent and more time-honored than the MFP approach.

Accelerated hypofractionated magnetic resonance-guided adaptive radiotherapy for oligoprogressive non-small cell lung cancer.

Given the positive results from recent randomized controlled trials in patients with oligometastatic, oligoprogressive, or oligoresidual disease, the role of radiotherapy has expanded in patients with metastatic non-small cell lung cancer (NSCLC). While small metastatic lesions are commonly treated with stereotactic body radiotherapy (SBRT), treatment of the primary tumor and involved regional lymph nodes may require prolonged fractionation schedules to ensure safety especially when treating larger volumes in proximity to critical organs-at-risk (OARs). We have developed an institutional MR-guided adaptive radiotherapy (MRgRT) workflow for these patients. We present a 71-year-old patient with stage IV NSCLC with oligoprogression of the primary tumor and associated regional lymph nodes in which MR-guided, online adaptive radiotherapy was performed, prescribing 60 Gy in 15 fractions. We describe our workflow, dosimetric constraints, and daily dosimetric comparisons for the critical OARs (esophagus, trachea, and proximal bronchial tree [PBT] maximum doses [D0.03cc]), in comparison to the original treatment plan recalculated on the anatomy of the day (i.e., predicted doses). During MRgRT, few fractions met the original dosimetric objectives: 6.6% for esophagus, 6.6% for PBT, and 6.6% for trachea. Online adaptive radiotherapy reduced the cumulative doses to the structures by 11.34%, 4.2%, and 5.62% when comparing predicted plan summations to the final delivered summation. Therefore, this case study presets a workflow and treatment paradigm for accelerated hypofractionated MRgRT due to the significant variations in daily dose to the central thoracic OARs to reduce treatment-related toxicity associated with radiotherapy.

OptImal Gamma kNife lIghTnIng sOlutioN (IGNITION) score to characterize the solution space of the Gamma Knife FIP optimizer for stereotactic radiosurgery.

OBJECTIVES: The objective of this study is to evaluate the user-defined optimization settings in the Fast Inverse Planning (FIP) optimizer in Leksell GammaPlan® and determine the parameters that result in the best stereotactic radiosurgery (SRS) plan quality for brain metastases, benign tumors, and arteriovenous malformations (AVMs). METHODS: Thirty patients with metastases and 30 with benign lesions-vestibular schwannoma, AVMs, pituitary adenoma, and meningioma-treated with SRS were evaluated. Each target was planned by varying the low dose (LD) and beam-on-time (BOT) penalties in increments of 0.1, from 0 to 1. The following plan quality metrics were recorded for each plan: Paddick conformity index (PCI), gradient index (GI), BOT, and maximum organ-at-risk (OAR) doses. A novel objective score matrix was calculated for each target using a linearly weighted combination of the aforementioned metrics. A histogram of optimal solutions containing the five best scores was extracted. RESULTS: A total of 7260 plans were analyzed with 121 plans per patient for the range of LD/BOT penalties. The ranges of PCI, GI, and BOT across all metastatic lesions were 0.58-0.97, 2.1-3.8, and 8.8-238 min, respectively, and were 0.13-0.97, 2.1-3.8, and 8.8-238 min, respectively, for benign lesions. The objective score matrix showed unique optimal solutions for metastatic lesions and benign lesions. Additionally, the plan metrics of the optimal solutions were significantly improved compared to the clinical plans for metastatic lesions with equivalent metrics for all other cases. CONCLUSION: In this study, FIP optimizer was evaluated to determine the optimal solution space to maximize PCI and minimize GI, BOT and OAR doses simultaneously for single metastatic/benign/non-neoplastic targets. The optimal solution chart was determined using a novel objective score which provides novice and expert planners a roadmap to generate the most optimal plans efficiently using FIP.

Treatment of glioblastoma using MRIdian® A3i BrainTx™: Imaging and treatment workflow demonstration.

For patients with newly diagnosed glioblastoma, the current standard-of-care includes maximal safe resection, followed by concurrent chemoradiotherapy and adjuvant temozolomide, with tumor treating fields. Traditionally, diagnostic imaging is performed pre- and post-resection, without additional dedicated longitudinal imaging to evaluate tumor volumes or other treatment-related changes. However, the recent introduction of MR-guided radiotherapy using the ViewRay MRIdian A3i system includes a dedicated BrainTx package to facilitate the treatment of intracranial tumors and provides daily MR images. We present the first reported case of a glioblastoma imaged and treated using this workflow. In this case, a 67-year-old woman underwent adjuvant chemoradiotherapy after gross total resection of a left frontal glioblastoma. The radiotherapy treatment plan consisted of a traditional two-phase design (46 Gy followed by a sequential boost to a total dose of 60 Gy at 2 Gy/fraction). The treatment planning process, institutional workflow, treatment imaging, treatment timelines, and target volume changes visualized during treatment are presented. This case example using our institutional A3i system workflow successfully allows for imaging and treatment of primary brain tumors and has the potential for margin reduction, detection of early disease progression, or to detect the need for dose adaptation due to interfraction tumor volume changes.