Commissioning a secondary dose calculation software for a 0.35 T MR-linac.

Secondary external dose calculations for a 0.35 T magnetic resonance image-guided radiation therapy (MRgRT) are needed within the radiation oncology community to follow safety standards set forth within the field. We evaluate the commercially available software, RadCalc, in its ability to accurately perform monitor unit dose calculations within a magnetic field. We also evaluate the potential effects of a 0.35 T magnetic field upon point dose calculations. Monitor unit calculations were evaluated with (wMag) and without (noMag) a magnetic field considerations in RadCalc for the ViewRay MRIdian. The magnetic field is indirectly accounted for by using asymmetric profiles for calculation. The introduction of double-stacked multi-leaf collimator leaves was also included in the monitor unit calculations and a single transmission value was determined. A suite of simple and complex geometries with a variety field arrangements were calculated for each method to demonstrate the effect of the 0.35 T magnetic field on monitor unit calculations. Finally, 25 patient-specific treatment plans were calculated using each method for comparison. All simple geometries calculated in RadCalc were within 2% of treatment planning system (TPS) values for both methods, except for a single noMag off-axis comparison. All complex muilt-leaf collimator (MLC) pattern calculations were within 5%. All complex phantom geometry calculations were within 5% except for a single field within a lung phantom at a distal point. For the patient calculations, the noMag method average percentage difference was 0.09 ± 2.5% and the wMag average percentage difference was 0.08 ± 2.5%. All results were within 5% for the wMag method. We performed monitor unit calculations for a 0.35 T MRgRT system using a commercially available secondary monitor unit dose calculation software and demonstrated minimal impact of the 0.35 T magnetic field on monitor unit dose calculations. This is the first investigation demonstrating successful calculations of dose using RadCalc in the low-field 0.35 T ViewRay MRIdian system.

Assessment of a novel commercial large field of view phantom for comprehensive MR imaging quality assurance of a 0.35T MRgRT system.

Consistent quality assurance (QA) programs are vital to MR-guided radiotherapy (MRgRT), for ensuring treatment is delivered accurately and the onboard MRI system is providing the expected image quality. However, daily imaging QA with a dedicated phantom is not common at many MRgRT centers, especially with large phantoms that cover a field of view (FOV), similar to the human torso. This work presents the first clinical experience with a purpose-built phantom for large FOV daily and periodic comprehensive quality assurance (QUASAR™ MRgRT Insight Phantom (beta)) from Modus Medical Devices Inc. (Modus QA) on an MRgRT system. A monthly American College of Radiology (ACR) QA phantom was also imaged for reference. Both phantoms were imaged on a 0.35T MR-Linac, a 1.5T Philips wide bore MRI, and a 3.0T Siemens MRI, with T1-weighted and T2-weighted acquisitions. The Insight phantom was imaged in axial and sagittal orientations. Image quality tests including geometric accuracy, spatial resolution accuracy, slice thickness accuracy, slice position accuracy, and image intensity uniformity were performed on each phantom, following their respective instruction manuals. The geometric distortion test showed similar distortions of -1.7 mm and -1.9 mm across a 190 mm and a 283 mm lengths for the ACR and MRgRT Insight phantoms, respectively. The MRgRT Insight phantom utilized a modulation transform function (MTF) for spatial resolution evaluation, which showed decreased performance on the lower B0 strength MRIs, as expected, and could provide a good daily indicator of machine performance. Both the Insight and ACR phantoms showed a match with scan parameters for slice thickness analysis. During the imaging and analysis of this novel MRgRT Insight phantom the authors found setup to be straightforward allowing for easy acquisition each day, and useful image analysis parameters for tracking MRI performance.

Clinical experience of MRI4D QUASAR motion phantom for latency measurements in 0.35T MR-LINAC.

PURPOSE: In MRgRT, accuracy of treatment depends on the gating latency, when real-time targeting and gating is enabled. Gating latency is dependent on image acquisition, processing time, accuracy, efficacy of target tracking algorithms, and radiation beam delivery latency. In this report, clinical experience of the MRI4D QUASAR motion phantom for latency measurements on a 0.35-T magnetic resonance-linear accelerator (MR-LINAC) with two imaging speeds and four tracking algorithms was studied. MATERIALS/METHODS: Beam-control latency was measured on a 0.35-T MR-LINAC system with four target tracking algorithms and two real-time cine imaging sequences [four and eight frames per second (FPS)]. Using an MR-compatible motion phantom, the delays between phantom beam triggering signal and linac radiation beam control signal were evaluated for three motion periods with a rigid target. The gating point was set to be 8 mm above the full exhalation position. The beam-off latency was measured for a total of 24 combinations of tracking algorithm, imaging FPS, and motion periods. The corresponding gating target margins were determined using the target motion speed multiplied by the beam-off latency. RESULTS: The largest measured beam-off latency was 302 ± 20 ms with the Large Deforming Targets (LDT) algorithm and 4 s motion period imaged with 8-FPS cine MRI. The corresponding gating uncertainty based on target motion speed was 3.0 mm. The range of the average beam-off latency was 128-243 ms in 4-FPS imaging and 47-302 ms in 8-FPS imaging. CONCLUSIONS: The gating latency was measured using an MRI4D QUASAR motion phantom in a 0.35-T MR-LINAC. The latency measurements include time delay related to MR imaging method, target tracking algorithm and system delay. The gating uncertainty was estimated based on the beam-off latency measurements and the target motion.

Evaluation of diffusion-weighted MRI and geometric distortion on a 0.35T MR-LINAC at multiple gantry angles.

Diffusion-weighted imaging (DWI) provides a valuable diagnostic tool for tumor evaluation. Yet, it is difficult to acquire daily MRI data sets in the traditional radiotherapy clinical setting due to patient burden and limited resources. However, integrated MRI radiotherapy treatment systems facilitate daily functional MRI acquisitions like DWI during treatment exams. Before ADC values from MR-RT systems can be used clinically their reproducibility and accuracy must be quantified. This study used a NIST traceable DWI phantom to verify ADC values acquired on a 0.35 T MR-LINAC system at multiple gantry angles. A diffusion-weighted echo planar imaging sequence was used for all image acquisitions, with b-values of 0, 500, 900, 2000 s/mm2 for the 1.5 T and 3.0 T systems and 0, 200, 500, 800 s/mm2 for the 0.35 T system. Images were acquired at multiple gantry angles on the MR-LINAC system from 0° to 330° in 30° increments to assess the impact of gantry angle on geometric distortion and ADC values. CT images, and three fiducial markers were used as ground truth for geometric distortion measurements. The distance between fiducial markers increased by as much as 7.2 mm on the MR-LINAC at gantry angle 60°. ADC values of deionized water vials from the 1.5 T and 3.0 T systems were 8.30 × 10-6  mm2 /s and -0.85 × 10-6  mm2 /s off, respectively, from the expected value of 1127 × 10-6  mm2 /s. The MR-LINAC system provided an ADC value of the pure water vials that was -116.63 × 10-6  mm2 /s off from the expected value of 1127 × 10-6  mm2 /s. The MR-LINAC also showed a variation in ADC across all gantry angles of 33.72 × 10-6  mm2 /s and 20.41 × 10-6  mm2 /s for the vials with expected values of 1127 × 10-6  mm2 /s and 248 × 10-6  mm2 /s, respectively. This study showed that variation of the ADC values and geometric information on the 0.35 T MR-LINAC system was dependent on the gantry angle at acquisition.

Optical emission-based phantom to verify coincidence of radiotherapy and imaging isocenters on an MR-linac.

PURPOSE: Demonstrate a novel phantom design using a remote camera imaging method capable of concurrently measuring the position of the x-ray isocenter and the magnetic resonance imaging (MRI) isocenter on an MR-linac. METHODS: A conical frustum with distinct geometric features was machined out of plastic. The phantom was submerged in a small water tank, and aligned using room lasers on a MRIdian MR-linac (ViewRay Inc., Cleveland, OH). The phantom physical isocenter was visualized in the MR images and related to the DICOM coordinate isocenter. To view the x-ray isocenter, an intensified CMOS camera system (DoseOptics LLC., Hanover, NH) was placed at the foot of the treatment couch, and centered such that the optical axis of the camera was coincident with the central axis of the treatment bore. Two or four 8.3mm x 24.1cm beams irradiated the phantom from cardinal directions, producing an optical ring on the conical surface of the phantom. The diameter of the ring, measured at the peak intensity, was compared to the known diameter at the position of irradiation to determine the Z-direction offset of the beam. A star-shot method was employed on the front face of the frustum to determine X-Y alignment of the MV beam. Known shifts were applied to the phantom to establish the sensitivity of the method. RESULTS: Couch translations, demonstrative of possible isocenter misalignments, on the order of 1mm were detectable for both the radiotherapy and MRI isocenters. Data acquired on the MR-linac demonstrated an average error of 0.28mm(N=10, R2 =0.997, σ=0.37mm) in established Z displacement, and 0.10mm(N=5, σ=0.34mm) in XY directions of the radiotherapy isocenter. CONCLUSIONS: The phantom was capable of measuring both the MRI and radiotherapy treatment isocenters. This method has the potential to be of use in MR-linac commissioning, and could be streamlined to be valuable in daily constancy checks of isocenter coincidence.

Characterization of radiotherapy component impact on MR imaging quality for an MRgRT system.

Radiotherapy components of an magnetic resonnace-guided radiotherapy (MRgRT) system can alter the magnetic fields, causing spatial distortion and image deformation, altering imaging and radiation isocenter coincidence and the accuracy of dose calculations. This work presents a characterization of radiotherapy component impact on MR imaging quality in terms of imaging isocenter variation and spatial integrity changes on a 0.35T MRgRT system, pre- and postupgrade of the system. The impact of gantry position, MLC field size, and treatment table power state on imaging isocenter and spatial integrity were investigated. A spatial integrity phantom was used for all tests. Images were acquired for gantry angles 0-330° at 30° increments to assess the impact of gantry position. For MLC and table power state tests all images were acquired at the home gantry position (330°). MLC field sizes ranged from 1.66 to 27.4 cm edge length square fields. Imaging isocenter shift caused by gantry position was reduced from 1.7 mm at gantry 150° preupgrade to 0.9 mm at gantry 120° postupgrade. Maximum spatial integrity errors were 0.5 mm or less pre- and postupgrade for all gantry angles, MLC field sizes, and treatment table power states. However, when the treatment table was powered on, there was significant reduction in SNR. This study showed that gantry position can impact imaging isocenter, but spatial integrity errors were not dependent on gantry position, MLC field size, or treatment table power state. Significant isocenter variation, while reduced postupgrade, is cause for further investigation.

Direct tumor visual feedback during free breathing in 0.35T MRgRT.

To present a tumor motion control system during free breathing using direct tumor visual feedback to patients in 0.35 T magnetic resonance-guided radiotherapy (MRgRT). We present direct tumor visualization to patients by projecting real-time cine MR images on an MR-compatible display system inside a 0.35 T MRgRT bore. The direct tumor visualization included anatomical images with a target contour and an auto-segmented gating contour. In addition, a beam-status sign was added for patient guidance. The feasibility was investigated with a six-patient clinical evaluation of the system in terms of tumor motion range and beam-on time. Seven patients without visual guidance were used for comparison. Positions of the tumor and the auto-segmented gating contour from the cine MR images were used in probability analysis to evaluate tumor motion control. In addition, beam-on time was recorded to assess the efficacy of the visual feedback system. The direct tumor visualization system was developed and implemented in our clinic. The target contour extended 3 mm outside of the gating contour for 33.6 ± 24.9% of the time without visual guidance, and 37.2 ± 26.4% of the time with visual guidance. The average maximum motion outside of the gating contour was 14.4 ± 11.1 mm without and 13.0 ± 7.9 mm with visual guidance. Beam-on time as a percentage was 43.9 ± 15.3% without visual guidance, and 48.0 ± 21.2% with visual guidance, but was not significantly different (P = 0.34). We demonstrated the clinical feasibility and potential benefits of presenting direct tumor visual feedback to patients in MRgRT. The visual feedback allows patients to visualize and attempt to minimize tumor motion in free breathing. The proposed system and associated clinical workflow can be easily adapted for any type of MRgRT.

MRI quality control for low-field MR-IGRT systems: Lessons learned.

PURPOSE: To present lessons learned from magnetic resonance imaging (MRI) quality control (QC) tests for low-field MRI-guided radiation therapy (MR-IGRT) systems. METHODS: MRI QC programs were established for low-field MRI-60 Co and MRI-Linac systems. A retrospective analysis of MRI subsystem performance covered system commissioning, operations, maintenance, and quality control. Performance issues were classified into three groups: (a) Image noise and artifact; (b) Magnetic field homogeneity and linearity; and (c) System reliability and stability. RESULTS: Image noise and artifacts were attributed to room noise sources, unsatisfactory system cabling, and broken RF receiver coils. Gantry angle-dependent magnetic field inhomogeneities were more prominent on the MRI-Linac due to the high volume of steel shielding in the gantry. B0 inhomogeneities measured in a 24-cm spherical phantom were <5 ppm for both MR-IGRT systems after using MRI gradient offset (MRI-GO) compensation on the MRI-Linac. However, significant signal dephasing occurred on the MRI-Linac while the gantry was rotating. Spatial integrity measurements were sensitive to gradient calibration and vulnerable to shimming. The most common causes of MR-IGRT system interruptions were software disconnects between the MRI and radiation therapy delivery subsystems caused by patient table, gantry, and multi-leaf collimator (MLC) faults. The standard deviation (SD) of the receiver coil signal-to-noise ratio was 1.83 for the MRI-60 Co and 1.53 for the MRI-Linac. The SD of the deviation from the mean for the Larmor frequency was 1.41 ppm for the MRI-60 Co and 1.54 ppm for the MRI-Linac. The SD of the deviation from the mean for the transmitter reference amplitude was 0.90% for the MRI-60 Co and 1.68% for the MRI-Linac. High SDs in image stability data corresponded to reports of spike noise. CONCLUSIONS: There are significant technological challenges associated with implementing and maintaining MR-IGRT systems. Most of the performance issues were identified and resolved during commissioning.

A method to reconstruct and apply 3D primary fluence for treatment delivery verification.

MOTIVATION: In this study, a method is reported to perform IMRT and VMAT treatment delivery verification using 3D volumetric primary beam fluences reconstructed directly from planned beam parameters and treatment delivery records. The goals of this paper are to demonstrate that 1) 3D beam fluences can be reconstructed efficiently, 2) quality assurance (QA) based on the reconstructed 3D fluences is capable of detecting additional treatment delivery errors, particularly for VMAT plans, beyond those identifiable by other existing treatment delivery verification methods, and 3) QA results based on 3D fluence calculation (3DFC) are correlated with QA results based on physical phantom measurements and radiation dose recalculations. METHODS: Using beam parameters extracted from DICOM plan files and treatment delivery log files, 3D volumetric primary fluences are reconstructed by forward-projecting the beam apertures, defined by the MLC leaf positions and modulated by beam MU values, at all gantry angles using first-order ray tracing. Treatment delivery verifications are performed by comparing 3D fluences reconstructed using beam parameters in delivery log files against those reconstructed from treatment plans. Passing rates are then determined using both voxel intensity differences and a 3D gamma analysis. QA sensitivity to various sources of errors is defined as the observed differences in passing rates. Correlations between passing rates obtained from QA derived from both 3D fluence calculations and physical measurements are investigated prospectively using 20 clinical treatment plans with artificially introduced machine delivery errors. RESULTS: Studies with artificially introduced errors show that common treatment delivery problems including gantry angle errors, MU errors, jaw position errors, collimator rotation errors, and MLC leaf position errors were detectable at less than normal machine tolerances. The reported 3DFC QA method has greater sensitivity than measurement-based QA methods. Statistical analysis-based Spearman's correlations shows that the 3DFC QA passing rates are significantly correlated with passing rates of physical phantom measurement-based QA methods. CONCLUSION: Among measurement-less treatment delivery verification methods, the reported 3DFC method is less demanding than those based on full dose re-calculations, and more comprehensive than those that solely checks beam parameters in treatment log files. With QA passing rates correlating to measurement-based passing rates, the 3DFC QA results could be useful for complementing the physical phantom measurements, or verifying treatment deliveries when physical measurements are not available. For the past 4+ years, the reported method has been implemented at authors' institution 1) as a complementary metric to physical phantom measurements for pretreatment, patient-specific QA of IMRT and VMAT plans, and 2) as an important part of the log file-based automated verification of daily patient treatment deliveries. It has been demonstrated to be useful in catching both treatment plan data transfer errors and treatment delivery problems.

Methods to model and predict the ViewRay treatment deliveries to aid patient scheduling and treatment planning.

A software tool is developed, given a new treatment plan, to predict treatment delivery time for radiation therapy (RT) treatments of patients on ViewRay magnetic resonance image-guided radiation therapy (MR-IGRT) delivery system. This tool is necessary for managing patient treatment scheduling in our clinic. The predicted treatment delivery time and the assessment of plan complexities could also be useful to aid treatment planning. A patient's total treatment delivery time, not including time required for localization, is modeled as the sum of four components: 1) the treatment initialization time; 2) the total beam-on time; 3) the gantry rotation time; and 4) the multileaf collimator (MLC) motion time. Each of the four components is predicted separately. The total beam-on time can be calculated using both the planned beam-on time and the decay-corrected dose rate. To predict the remain-ing components, we retrospectively analyzed the patient treatment delivery record files. The initialization time is demonstrated to be random since it depends on the final gantry angle of the previous treatment. Based on modeling the relationships between the gantry rotation angles and the corresponding rotation time, linear regression is applied to predict the gantry rotation time. The MLC motion time is calculated using the leaves delay modeling method and the leaf motion speed. A quantitative analysis was performed to understand the correlation between the total treatment time and the plan complexity. The proposed algorithm is able to predict the ViewRay treatment delivery time with the average prediction error 0.22min or 1.82%, and the maximal prediction error 0.89 min or 7.88%. The analysis has shown the correlation between the plan modulation (PM) factor and the total treatment delivery time, as well as the treatment delivery duty cycle. A possibility has been identified to significantly reduce MLC motion time by optimizing the positions of closed MLC pairs. The accuracy of the proposed prediction algorithm is sufficient to support patient treatment appointment scheduling. This developed software tool is currently applied in use on a daily basis in our clinic, and could also be used as an important indicator for treatment plan complexity.

A software tool to automatically assure and report daily treatment deliveries by a cobalt-60 radiation therapy device.

The aims of this study were to develop a method for automatic and immediate verification of treatment delivery after each treatment fraction in order to detect and correct errors, and to develop a comprehensive daily report which includes delivery verification results, daily image-guided radiation therapy (IGRT) review, and information for weekly physics reviews. After systematically analyzing the requirements for treatment delivery verification and understanding the available information from a commercial MRI-guided radiotherapy treatment machine, we designed a procedure to use 1) treatment plan files, 2) delivery log files, and 3) beam output information to verify the accuracy and completeness of each daily treatment delivery. The procedure verifies the correctness of delivered treatment plan parameters including beams, beam segments and, for each segment, the beam-on time and MLC leaf positions. For each beam, composite primary fluence maps are calculated from the MLC leaf positions and segment beam-on time. Error statistics are calculated on the fluence difference maps between the plan and the delivery. A daily treatment delivery report is designed to include all required information for IGRT and weekly physics reviews including the plan and treatment fraction information, daily beam output information, and the treatment delivery verification results. A computer program was developed to implement the proposed procedure of the automatic delivery verification and daily report generation for an MRI guided radiation therapy system. The program was clinically commissioned. Sensitivity was measured with simulated errors. The final version has been integrated into the com-mercial version of the treatment delivery system. The method automatically verifies the EBRT treatment deliveries and generates the daily treatment reports. Already in clinical use for over one year, it is useful to facilitate delivery error detection, and to expedite physician daily IGRT review and physicist weekly chart review.

Comparison of onboard low-field magnetic resonance imaging versus onboard computed tomography for anatomy visualization in radiotherapy.

BACKGROUND: Onboard magnetic resonance imaging (OB-MRI) for daily localization and adaptive radiotherapy has been under development by several groups. However, no clinical studies have evaluated whether OB-MRI improves visualization of the target and organs at risk (OARs) compared to standard onboard computed tomography (OB-CT). This study compared visualization of patient anatomy on images acquired on the MRI-(60)Co ViewRay system to those acquired with OB-CT. MATERIAL AND METHODS: Fourteen patients enrolled on a protocol approved by the Institutional Review Board (IRB) and undergoing image-guided radiotherapy for cancer in the thorax (n = 2), pelvis (n = 6), abdomen (n = 3) or head and neck (n = 3) were imaged with OB-MRI and OB-CT. For each of the 14 patients, the OB-MRI and OB-CT datasets were displayed side-by-side and independently reviewed by three radiation oncologists. Each physician was asked to evaluate which dataset offered better visualization of the target and OARs. A quantitative contouring study was performed on two abdominal patients to assess if OB-MRI could offer improved inter-observer segmentation agreement for adaptive planning. RESULTS: In total 221 OARs and 10 targets were compared for visualization on OB-MRI and OB-CT by each of the three physicians. The majority of physicians (two or more) evaluated visualization on MRI as better for 71% of structures, worse for 10% of structures, and equivalent for 14% of structures. 5% of structures were not visible on either. Physicians agreed unanimously for 74% and in majority for > 99% of structures. Targets were better visualized on MRI in 4/10 cases, and never on OB-CT. CONCLUSION: Low-field MR provides better anatomic visualization of many radiotherapy targets and most OARs as compared to OB-CT. Further studies with OB-MRI should be pursued.

World's First Application of MR-Guidance for Radiotherapy.

Radiotherapy localization is the process by which patient treatments are aligned on a daily basis. Localization has hiistorically been accomplished using 2-dimensional x-ray images, or cone-beam CT- imaging which permits excellent visualization of bony anatomy, but suboptimal soft-tissue imaging. The Department of Radiation Oncology at Washington University recently implemented the world's first MR-Image Guided Radiation Therapy program (MR-IGRT), which utilizes a O.35T MR scanner integrated with three 6"Co heads for treatment delivery. A high-resolution volumetric MR image is acquired for each patient at the time of daily treatment setup, which allows localization based on soft-tissue anatomy, and modification to the treatment plan when required while the patient is on the treatment table. Herein, we review principles of radiotherapy localization, describe implementation of the world's first MR-IGRT program, and present future directions where MR-IGRT may be applied for patient treatments.

Effects of the COVID-19 Pandemic on University Students' Mental Health: A Literature Review.

This review aims to focus on the effects of COVID-19 on university students' mental health and deepen our understanding of it. The conclusions are based on the review of 32 studies conducted during the pandemic. This review confirms that university students were at high risk for mental health disorders, heightened stress, and increased sleep comorbidities both pre-pandemic and during the pandemic. This literature review confirmed a few universal trends, i.e., increased stress, anxiety, and depression, during the pandemic. The rates of insomnia, obsessive-compulsive disorder, and suicidal ideation also went up. Overall, female students are at a disadvantage in the development of mental health issues. Male students coped better but may be at higher risk for lethality in suicidal ideation. Students with a history of mental health issues and other comorbidities prior to the pandemic had worse outcomes compared to healthy individuals. The study points to a strong positive correlation between fear and increased rates of stress, anxiety, and insomnia. There is also a positive correlation between declining mental health and online learning. A strong negative correlation was present between physical activity and depressive symptoms. These findings are universal across many countries and regions where the studies occurred.

A pilot study of same-day MRI-only simulation and treatment with MR-guided adaptive palliative radiotherapy (MAP-RT).

We conducted a prospective pilot study evaluating the feasibility of same day MRI-only simulation and treatment with MRI-guided adaptive palliative radiotherapy (MAP-RT) for urgent palliative indications (NCT#03824366). All (16/16) patients were able to complete 99% of their first on-table attempted fractions, and no grades 3-5 toxicities occurred.

First treatments for Lattice stereotactic body radiation therapy using magnetic resonance image guided radiation therapy.

Two abdominal patients were treated with Lattice stereotactic body radiation therapy (SBRT) using magnetic resonance guided radiation therapy (MRgRT). This is one of the first reported treatments of Lattice SBRT with the use of MRgRT. A description of the treatment approach and planning considerations were incorporated into this report. MRgRT Lattice SBRT delivered similar planning quality metrics to established dosimetric parameters for Lattice SBRT. Increased signal intensity were seen in the MRI treatments for one of the patients during the course of treatment.

Clinical outcomes of patients with unresectable primary liver cancer treated with MR-guided stereotactic body radiation Therapy: A Six-Year experience.

Purpose: Magnetic resonance-guided stereotactic body radiation therapy (MRgSBRT) with optional online adaptation has shown promise in delivering ablative doses to unresectable primary liver cancer. However, there remain limited data on the indications for online adaptation as well as dosimetric and longer-term clinical outcomes following MRgSBRT. Methods and Materials: Patients with unresectable hepatocellular carcinoma (HCC), cholangiocarcinoma (CCA), and combined biphenotypic hepatocellular-cholangiocarcinoma (cHCC-CCA) who completed MRgSBRT to 50 Gy in 5 fractions between June of 2015 and December of 2021 were analyzed. The necessity of adaptive techniques was evaluated. The cumulative incidence of local progression was evaluated and survival and competing risk analyses were performed. Results: Ninety-nine analyzable patients completed MRgSBRT during the study period and 54 % had planning target volumes (PTVs) within 1 cm of the duodenum, small bowel, or stomach at the time of simulation. Online adaptive RT was used in 53 % of patients to correct organ-at-risk constraint violation and/or to improve target coverage. In patients who underwent adaptive RT planning, online replanning resulted in superior target coverage when compared to projected, non-adaptive plans (median coverage ≥ 95 % at 47.5 Gy: 91 % [IQR: 82-96] before adaptation vs 95 % [IQR: 87-99] after adaptation, p < 0.01). The median follow-up for surviving patients was 34.2 months for patients with HCC and 10.1 months for patients with CCA/cHCC-CCA. For all patients, the 2-year cumulative incidence of local progression was 9.8 % (95 % CI: 1.5-18 %) for patients with HCC and 9.0 % (95 % CI: 0.1-18) for patients with CCA/cHCC-CCA. Grade 3 through 5 acute and late clinical gastrointestinal toxicities were observed in < 10 % of the patients. Conclusions: MRgSBRT, with the option for online adaptive planning when merited, allows delivery of ablative doses to primary liver tumors with excellent local control with acceptable toxicities. Additional studies evaluating the efficacy and safety of MRgSBRT in the treatment of primary liver cancer are warranted.

MR-Guided Radiation Therapy With Concurrent Gemcitabine/Nab-Paclitaxel Chemotherapy in Inoperable Pancreatic Cancer: A TITE-CRM Phase I Trial.

PURPOSE: Ablative radiation therapy for borderline resectable or locally advanced pancreatic ductal adenocarcinoma (BR/LA-PDAC) may limit concurrent chemotherapy dosing and usually is only safely deliverable to tumors distant from gastrointestinal organs. Magnetic resonance guided radiation therapy may safely permit radiation and chemotherapy dose escalation. METHODS AND MATERIALS: We conducted a single-arm phase I study to determine the maximum tolerated dose of ablative hypofractionated radiation with full-dose gemcitabine/nab-paclitaxel in patients with BR/LA-PDAC. Patients were treated with gemcitabine/nab-paclitaxel (1000/125 mg/m2) x 1c then concurrent gemcitabine/nab-paclitaxel and radiation. Gemcitabine/nab-paclitaxel and radiation doses were escalated per time-to-event continual reassessment method from 40 to 45 Gy 25 fxs with chemotherapy (600-800/75 mg/m2) to 60 to 67.5 Gy/15 fractions and concurrent gemcitabine/nab-paclitaxel (1000/100 mg/m2). The primary endpoint was maximum tolerated dose of radiation as defined by 60-day dose limiting toxicity (DLT). DLT was treatment-related G5, G4 hematologic, or G3 gastrointestinal requiring hospitalization >3 days. Secondary endpoints included resection rates, local progression free survival (LPFS), distant metastasis free survival (DMFS), and overall survival (OS). RESULTS: Thirty patients enrolled (March 2015-February 2019), with 26 evaluable patients (2 progressed before radiation, 1 was determined ineligible for radiation during planning, 1 withdrew consent). One DLT was observed. The DLT rate was 14.1% (3.3%-24.9%) with a maximum tolerated dose of gemcitabine/nab-paclitaxel (1000/100 mg/m2) and 67.5 Gy/15 fractions. At a median follow-up of 40.6 months for living patients the median OS was 14.5 months (95% confidence interval [CI], 10.9-28.2 months). The median OS for patients with Eastern Collaborative Oncology Group 0 and carbohydrate antigen 19-9 <90 were 34.1 (95% CI, 13.6-54.1) and 43.0 (95% CI, 8.0-not reached) months, respectively. Two-year LPFS and DMFS were 85% (95% CI, 63%-94%) and 57% (95% CI, 34%-73%), respectively. CONCLUSIONS: Full-dose gemcitabine/nab-paclitaxel with ablative magnetic resonance guided radiation therapy dosing is safe in patients with BR/LA-PDAC, with promising LPFS and DMFS.

Assessing Inter-Fraction Changes in The Size and Position of The Penile Bulb During Daily MR-Guided Radiation Therapy to The Prostate Bed: Do We Need to Adjust How We Plan Radiation in The Post-Radical Prostatectomy Setting to Reduce Risk of Erectile Dysfunction?

BACKGROUND: We evaluated inter-fraction penile bulb (PB) changes in prostate cancer (PCa) patients undergoing MR-guided RT in the post-radical prostatectomy (RP) setting. MATERIALS AND METHODS: 10 patients with PCa status-post RP received MR-guided RT from 2017-2019. Patients received daily setup volumetric MRI scans prior to RT delivery for alignment and target localization. Setup MRI datasets from Fx 1, Fx 19, and Fx 37 were fused for each patient based on soft tissue anatomy. The PB was contoured on each MRI. Data on volume (cc), superior/inferior positional change (cm), and mean dose (Gy) was collected. Differences were assessed by Student's t-test (sig. p<0.05). RESULTS: The mean PB volume change from Fx 1→ 19 was +0.34 ± 0.34 cc (p=0.11) and from Fx 1→ 37 was +0.22 ± 0.28 cc (p=0.31). The mean positional change from Fx 1→ 19 was +0.08±0.26 cm (p=0.37) and from Fx 1→ 37 was +0.05 ±0.25 cm (p=0.57). The mean change in mean PB dose from Fx 1→ 19 was +0.19±4.86 Gy (p=0.98) and from Fx 1→ 37 was -1.51≖7.46 Gy (p=0.88). CONCLUSION: We present the first study evaluating inter-fraction changes to the PB during MR-guided RT. We found no clinically meaningful difference in the volume, positional change, or mean dose during RT in the post-prostatectomy setting, suggesting that PB organ motion may not need to be accounted for in radiation treatment planning.