Intrafraction Motion Research Articles

Setup and intra-fractional motion measurements using surface scanning in head and neck cancer radiotherapy– A feasibility study

Background and purposeSurface-guided radiotherapy (SGRT) is applied to improve patient set-up and to monitor intra-fraction motion. Head and neck cancer (H&N) patients are usually fixated using 5-point thermoplastic masks, that are experienced as uncomfortable or even stressful. Therefore, the feasibility of irradiating H&N patients without a mask by using SGRT was examined. Material and methodsNineteen H&N patients were included in a simulation study. Once a week, before the standard treatment, a maskless treatment was simulated, using SGRT for setup and intrafraction motion monitoring. Initial patient setup accuracy and intrafraction motion was determined using ConeBeam CT (CBCT) images as well as SGRT before and after the (simulated) treatment. The clinical target volume to planning target volume (CTV-PTV) margin for intrafraction motion was calculated. Using patient questionnaires, the patient-friendliness H&N irradiation with and without mask was determined. ResultsMaskless setup with SGRT and CBCT was as accurate as with a mask. SGRT showed that intrafraction motion was gradual during the treatment. The CTV-PTV margin correcting for intrafraction motion was 1.7 mm for maskless treatment without interventions, and 1.2 mm if corrected for motions > 2 mm. For 19 % of fractions, the intrafraction motion, as detected by both SGRT and CBCT, was larger than 2 mm in at least one direction. Sixteen patients preferred maskless treatment, while 3 worried they would move too much. ConclusionsUsing SGRT and a standard head rest resulted in a patient-friendly treatment with accurate patient setup and acceptably small intrafraction motion for H&N patients.

Patient Cranial Angle and Intrafractional Stability in CyberKnife Robotic Radiosurgery: A Retrospective Analysis.

Purpose: The aim of this study was to investigate whether variations in cranial angles and treatment accuracy during CyberKnife robotic radiosurgery necessitate adjustment of the margins of the planning target volume. Patients and Methods: Data from 66 patients receiving CyberKnife treatment for brain tumors were retrospectively analyzed. Patients were immobilized using a thermoplastic mask and headrest. The cranial angle was measured on planning CT and patients were divided into 2 groups: ≤10° (Group A) and >10° (Group B). Intrafractional motion was recorded using the CyberKnife tracking system over 50 min. Translational and rotational errors were compared between groups, and planning target volume margins were calculated. Results: In Group A, significant translational error differences were found along with the X-axis over time (P < .02). In Group B, significant differences occurred along with the Z-axis (P < .03). No significant rotational or 3-dimensional vector differences were found in either group. Group A had significantly lower Y-axis (P < .045) and roll axis (P < .005) errors compared to Group B. Estimated planning target volume margins in Group A were 0.56 mm (X), 0.46 mm (Y), and 0.47 mm (Z). In Group B, margins were 0.62 mm (X), 0.48 mm (Y), and 0.46 mm (Z). Margins covering 95% of intrafraction motion were 0.49 to 0.50 mm (X, Y, Z) and 0.69 mm (3-dimensional vector) for Group A, and 0.48 to 0.60 mm and 0.79 mm for Group B. With a 1-mm margin, complete coverage was achieved in Group A while 2.1% of vectors in Group B exceeded 1 mm. Conclusion: Adjusting cranial angle to ≤10° during thermoplastic mask molding provided better or similar intrafractional stability compared to >10°.

Detectability and intra-fraction motion of individual elective lymph nodes in head and neck cancer patients on the Magnetic Resonance Image guided linear accelerator

Background and purposeIndividual elective lymph node irradiation instead of elective neck irradiation is a new concept for head-and-neck cancer (HNC) patients developed for the Magnetic Resonance Image guided linear accelerator (MR-linac). To prepare this, the detectability, volume changes and intra-fraction motion of elective lymph nodes on the MR-linac was assessed. Materials and methodsA total of 15 HNC patients underwent diagnostic pre-treatment MRI. Additionally, two MR-linac scans were obtained with a 10-minute time difference in the first week of radiation treatment. Elective lymph node contours inside lymph node levels (Ib-V) were segmented on the pre-treatment MRI and the MR-linac scans and compared on number and maximal transversal diameter. Intra-fraction motion of elective lymph nodes on the MR-linac was estimated using Center of Mass (COM) distances and incremental isotropic expansion of lymph node segmentations. ResultsOf all 679 detected lymph nodes on the pre-treatment MRI, eight lymph nodes were not detectable on the first MR-linac scan and 16 new lymph nodes were detected. Lymph node diameters between the pre-treatment MRI scan and the MR-linac scan varied from −0.19 to + 0.13 mm. COM distances varied from 1.2 to 1.7 mm and lymph node contours had to be expanded with 3 mm. ConclusionsNearly all elective lymph nodes were detectable on the 1.5T MR-linac scan with no major changes in target volumes compared to the pre-treatment MRI. Simulated intra-fraction motion during the MR-linac scans was smaller than the 5-mm margin that will be used in the first elective lymph node radiation treatment.

Quantifying Intrafraction Motion and the Impact of Gating for Magnetic Resonance Imaging-Guided Stereotactic Radiation therapy for Prostate Cancer: Analysis of the Magnetic Resonance Imaging Arm From the MIRAGE Phase 3 Randomized Trial

Real-time intrafraction tracking/gating is an integral component of magnetic resonance imaging-guided radiation therapy (MRgRT) and may have contributed to the acute toxicity reduction during prostate stereotactic body radiation therapy observed on the MRgRT-arm of the MIRAGE (MAGNETIC RESONANCE IMAGING-GUIDED Stereotactic Body Radiotherapy for Prostate Cancer) randomized trial (NCT04384770). Herein we characterized intrafraction prostate motion and assessed gating effectiveness. Seventy-nine patients were treated on an MR-LINAC. Real-time cine imaging was acquired at 4Hz in a sagittal plane. If >10% of the prostate area moved outside of a 3-mm gating boundary, an automatic beam hold was initiated. An in-house tool was developed to retrospectively extract gating signal for all patients and identify the tracked prostate in each cine frame for a subgroup of 40 patients. The fraction of time the prostate was within the gating window was defined as the gating duty cycle (GDC). A total of 391 treatments from 79 patients were analyzed. Median GDC was 0.974 (IQR, 0.916-0.983). Fifty (63.2%) and 24 (30.4%) patients had at least 1 fraction with GDC ≤0.9 and GDC ≤0.8, respectively. Incidence of low GDC fractions among patients appeared stochastic. Patients with minimum GDC <0.8 trended toward more frequent grade 2 genitourinary toxicity compared with those with minimum GDC >0.8 (38% vs 18%, P = .065). Prostate intrafraction motion was mostly along the bladder-rectum axis and predominantly in the superior-anterior direction. Motion in the inferior-posterior direction was associated with significantly higher rate of acute grade 2 genitourinary toxicity (66.7% vs 13.9%, P = .001). Gating limited mean prostate motion during treatment delivery in fractions with a GDC <0.9 (<0.8) to 2.9 mm (2.9 mm) versus 4.1 mm (4.7 mm) for ungated motion. Fractions with large intrafraction motion were associated with increased toxicity and their occurrence among patients appears stochastic. Real-time tracking/gating effectively mitigated this motion and is likely a major contributing factor of acute toxicity reduction associated with MRgRT.

Dosimetric Comparison of 3D Conformal Radiotherapy (3D-CRT), Intensity-Modulated Radiotherapy (IMRT), and Volumetric-Modulated Arc Therapy (VMAT) in Cardiac-Sparing Whole Lung Irradiation.

Introduction Whole lung irradiation (WLI) is used for the treatment of lung metastasis in Wilms tumor and Ewing sarcoma; however, cardiac complications are one of the concerns. We report the dosimetric advantages of WLI using volumetric-modulated arc therapy (VMAT) and present a dosimetric comparison of VMAT with anteroposterior-posteroanterior (AP-PA) and static-field intensity-modulated radiation therapy (IMRT). Additionally, we evaluated the dosimetric impact of respiratory motion and intra-fractional motion during VMAT treatment. Methods Seven patients were recruited in this study. AP-PA, IMRT, one-isocenter (1-IC) VMAT, and 2-IC VMAT were planned on the maximum inspiration and expiration CT, respectively. The prescribed dose was 15 Gy in 10 fractions. To determine the effects of respiratory motion, the CT series was replaced and the dose was evaluatedwhile maintaining the beam information. To determine the effect of patient motion, perturbed dose calculations were performed using a two-IC VMAT. The perturbation doses were calculated by shifting only the IC of the one side beam by 3mm or 5 mm in the right-to-left (RL) direction. Results The mean heart dose was 1467.0 cGy, 790.0 cGy, 764.2 cGy, and 738.4 cGy for AP-PA, IMRT, 1-IC VMAT, and 2-IC VMAT, respectively. When the expiration CT plan was recalculated with inspiration CT, Dmax increased approximately by 8%. In the 2-IC VMAT plan, the D50%, D98%, and D2% dose differences were within ±2%, even with a 5 mm IC shift. Conclusion We confirmed a significant dosimetric advantage of VMAT over other techniques. 2-IC VMAT should be consideredan effective treatment option during irradiation for large target volumes.

Determination of internal target volume with Cine-MRI sequence for prostate MRI-Guided radiotherapy.

In prostate radiotherapy, the intrafractional target motion negatively affects treatment accuracy. Generating internal target volume (ITV) using four-dimensional (4D) images may resolve the issue of intrafractional target motion induced by bladder filling and bowel movement. However, no 4D imaging techniques suitable for the prostate are currently available in clinical practice. This study aimed to determine the ITV based on cine magnetic resonance imaging (MRI) sequence for intrafractional target motion management in prostate MRI-guided radiotherapy. A reference ITV was generated in simulation process. Then, the reference ITV was adapted with cine MRI sequence before online planning in each fraction. Finally, the reference ITV was updated with the cine MRI sequence acquired during beam delivery after each fraction. Cine MRI sequences and positioning three-dimensional (3D) MRI from 35 patients were retrospectively collected. Clinical target volume (CTV) coverage was computed according to the two-dimensional contour of CTV and ITV on cine MRI images. Relative target size was calculated as the ratio of the volume of ITV and CTV. Isotropic planning target volume (PTV; 5mm margin) and anisotropic PTV (3mm margin in the posterior direction and 5mm margin in other directions) were generated for comparison. The CTV coverage rate of the proposed ITV had a mean value of 98.61%±0.51%, whereas the CTV coverage rates of the isotropic and anisotropic PTVs were 97.43%±0.41% and 96.58%±0.73%, respectively. The proposed ITV had a relative target size of 1.79±0.17, whereas the anisotropic and isotropic PTVs had relative target sizes of 1.92±0.12 and 2.21±0.19, respectively. For both the CTV coverage rate and target relative size, significant differences were observed between the proposed ITV and the other two PTVs (p<0.05). The ITV achieved higher CTV coverage with smaller size than conventional isotropic and anisotropic PTVs, indicating that it can effectively deal with the intrafractional movement of the prostate.

Characteristics of breathing-adapted gating using surface guidance for use in particle therapy: A phantom-based end-to-end test from CT simulation to dose delivery.

To account for intra-fractional tumor motion during dose delivery in radiotherapy, various treatment strategies are clinically implemented such as breathing-adapted gating and irradiating the tumor during specific breathing phases. In this work, we present a comprehensive phantom-based end-to-end test of breathing-adapted gating utilizing surface guidance for use in particle therapy. A commercial dynamic thorax phantom was used to reproduce regular and irregular breathing patterns recorded by the GateRT respiratory monitoring system. The amplitudes and periods of recorded breathing patterns were analysed and compared to planned patterns (ground-truth). In addition, the mean absolute deviations (MAD) and Pearson correlation coefficients (PCC) between the measurements and ground-truth were assessed. Measurements of gated and non-gated irradiations were also analysed with respect to dosimetry and geometry, and compared to treatment planning system (TPS). Further, the latency time of beam on/off was evaluated. Compared to the ground-truth, measurements performed with GateRT showed amplitude differences between 0.03±0.02mm and 0.26±0.03mm for regular and irregular breathing patterns, whilst periods of both breathing patterns ranged with a standard deviation between 10 and 190ms. Furthermore, the GateRT software precisely acquired breathing patterns with a maximum MAD of 0.30±0.23mm. The PCC constantly ranged between 0.998 and 1.000. Comparisons between TPS and measured dose profiles indicated absolute mean dose deviations within institutional tolerances of±5%. Geometrical beam characteristics also varied within our institutional tolerances of 1.5mm. The overall time delays were<60ms and thus within both recommended tolerances published by ESTRO and AAPM of 200 and 100ms, respectively. In this study, a non-invasive optical surface-guided workflow including image acquisition, treatment planning, patient positioning and gated irradiation at an ion-beam gantry was investigated, and shown to be clinically viable. Based on phantom measurements, our results show a clinically-appropriate spatial, temporal, and dosimetric accuracy when using surface guidance in the clinical setting, and the results comply with international and institutional guidelines and tolerances.

Pancreatic SABR using peritumoral fiducials, triggered imaging and breath-hold.

Background: We aim to present our linear accelerator-based workflow for pancreatic stereotactic ablative radiotherapy (SABR) in order to address the following issues: intrafractional organ motion management, Cone Beam CT (CBCT) image quality, residual errors with dosimetric consequences, treatment time, and clinical results. Methods: Between 2016 and 2021, 14 patients with locally advanced pancreatic cancer were treated with induction chemotherapy and SABR using volumetric modulated arc therapy (VMAT). Internal target volume (ITV) concept (5), phase-gated (4), or breath hold (5) techniques were used. Treatment was verified by CBCT before and after irradiation, while tumor motion was monitored and controlled by kV triggered imaging and beam hold using peritumoral surgical clips. Beam interruptions and treatment time were recorded. The CBCT image quality was scored and supplemented by an agreement analysis (Krippendorff's-α) of breath-hold CBCT images to determine the position of OARs relative to the planning risk volumes (PRV). Residual errors and their dosimetry impact were also calculated. Progression free (PFS) and overall survival (OS) were assessed by the Kaplan-Meier analysis with acute and late toxicity reporting (CTCAEv4). Results: On average, beams were interrupted once (range: 0-3) per treatment session on triggered imaging. The total median treatment time was 16.7 ± 10.8min, significantly less for breath-hold vs. phase-gated sessions (18.8 ± 6.2 vs. 26.5 ± 13.4, p < 0.001). The best image quality was achieved by breath hold CBCT. The Krippendorff's-α test showed a strong agreement among five radiation therapists (mean K-α value: 0.8 (97.5%). The mean residual errors were <0.2cm in each direction resulting in an average difference of <2% in dosimetry for OAR and target volume. Two patients received offline adaptation. The median OS/PFS after induction chemotherapy and SABR was 20/12months and 15/8months. No Gr. ≥2 acute/late RT-related toxicity was noted. Conclusion: Linear accelerator based pancreatic SABR with the combination of CBCT and triggered imaging + beam hold is feasible. Peritumoral fiducials improve utility while breath-hold CBCT provides the best image quality at a reasonable treatment time with offline adaptation possibilities. In well-selected cases, it can be an effective alternative in clinics where CBCT/MRI-guided online adaptive workflow is not available.

Impact of intrafraction motion in pancreatic cancer treatments with MR-guided adaptive radiation therapy.

The total time of radiation treatment delivery for pancreatic cancer patients with daily online adaptive radiation therapy (ART) on an MR-Linac can range from 50 to 90min. During this period, the target and normal tissues undergo changes due to respiration and physiologic organ motion. We evaluated the dosimetric impact of the intrafraction physiological organ changes. Ten locally advanced pancreatic cancer patients were treated with 50 Gy in five fractions with intensity-modulated respiratory-gated radiation therapy on a 0.35-T MR-Linac. Patients received both pre- and post-treatment volumetric MRIs for each fraction. Gastrointestinal organs at risk (GI-OARs) were delineated on the pre-treatment MRI during the online ART process and retrospectively on the post-treatment MRI. The treated dose distribution for each adaptive plan was assessed on the post-treatment anatomy. Prescribed dose volume histogram metrics for the scheduled plan on the pre-treatment anatomy, the adapted plan on the pre-treatment anatomy, and the adapted plan on post-treatment anatomy were compared to the OAR-defined criteria for adaptation: the volume of the GI-OAR receiving greater than 33 Gy (V33Gy) should be ≤1 cubic centimeter. Across the 50 adapted plans for the 10 patients studied, 70% were adapted to meet the duodenum constraint, 74% for the stomach, 12% for the colon, and 48% for the small bowel. Owing to intrafraction organ motion, at the time of post-treatment imaging, the adaptive criteria were exceeded for the duodenum in 62% of fractions, the stomach in 36%, the colon in 10%, and the small bowel in 48%. Compared to the scheduled plan, the post-treatment plans showed a decrease in the V33Gy, demonstrating the benefit of plan adaptation for 66% of the fractions for the duodenum, 95% for the stomach, 100% for the colon, and 79% for the small bowel. Post-treatment images demonstrated that over the course of the adaptive plan generation and delivery, the GI-OARs moved from their isotoxic low-dose region and nearer to the dose-escalated high-dose region, exceeding dose-volume constraints. Intrafraction motion can have a significant dosimetric impact; therefore, measures to mitigate this motion are needed. Despite consistent intrafraction motion, plan adaptation still provides a dosimetric benefit.

Setup Uncertainty of Pediatric Brain Tumor Patients Receiving Proton Therapy: A Prospective Study.

This study quantifies setup uncertainty in brain tumor patients who received image-guided proton therapy. Patients analyzed include 165 children, adolescents, and young adults (median age at radiotherapy: 9 years (range: 10 months to 24 years); 80 anesthetized and 85 awake) enrolled in a single-institution prospective study from 2020 to 2023. Cone-beam computed tomography (CBCT) was performed daily to calculate and correct manual setup errors, once per course after setup correction to measure residual errors, and weekly after treatments to assess intrafractional motion. Orthogonal radiographs were acquired consecutively with CBCT for paired comparisons of 40 patients. Translational and rotational errors were converted from 6 degrees of freedom to a scalar by a statistical approach that considers the distance from the target to the isocenter. The 95th percentile of setup uncertainty was reduced by daily CBCT from 10 mm (manual positioning) to 1-1.5 mm (after correction) and increased to 2 mm by the end of fractional treatment. A larger variation existed between the roll corrections reported by radiographs vs. CBCT than for pitch and yaw, while there was no statistically significant difference in translational variation. A quantile mixed regression model showed that the 95th percentile of intrafractional motion was 0.40 mm lower for anesthetized patients (p=0.0016). Considering additional uncertainty in radiation-imaging isocentricity, the commonly used total plan robustness of 3 mm against positional uncertainty would be appropriate for our study cohort.

RADT-47. MARGIN REDUCTION WITH THE INTRODUCTION OF INTRA-FRACTIONAL MONITORING USING IDENTIFY SGRT FOR FRAMELESS STEREOTACTIC CRANIAL RADIOSURGERY (SRS)

Abstract The purpose of this study was to evaluate the potential for margin reduction in clinical treatment settings based on the accuracy of Varian Identify SGRT (Surface-Guided Radiation Therapy). The study considered various factors such as patient setup variations, intrafraction movement, and unique facial features. Identify version 2.3.1 was installed on a Truebeam v2.7 system and commissioned according to AAPM TG3021 test recommendations. Identify generated reports on patient offsets in all six degrees of freedom during motion monitoring. These offsets were retrospectively compared with radiographic images (CBCT and MV planar images) to determine the accuracy of patient positioning achieved using surface guidance. A retrospective analysis of 36 patients was performed for a total of 125 fractions. The characteristics of the patient cohort (age range from 39 – 92 years) consisted of a mixture of 8 benign, 28 malignant lesions, 11 single, 25 standard fully-fractionated treatments and anatomical sites such as parietal, frontal, ventricle, base of skull, pons and acoustic neuromas. RESULTS: show that for this clinical cohort, the variance between Identify and radiographic imaging ranges from -0.02 to 0.08 cm, -0.09 to 0.10 cm, -0.09 to 0.09 cm and -0.81 to 0.74 degrees for the vertical, longitudinal, lateral and rotation respectively. This average variance in the translational axes is 0.0cm ± 0.0014 cm, indicating no directional preference. The 3D vector of the displacement detected achievable by Identify is 1 mm within a 95% confidence interval (CI). Based on the findings, the researchers concluded that a minimum GTV-PTV (Gross Tumor Volume-Planning Target Volume) margin of 1 mm is appropriate for intrafraction monitoring with Identify SGRT on the TrueBeam system for stereotactic cranial treatments. This information can increase the radiation oncologist's confidence in patient positioning during treatment delivery and potentially lead to a decrease in the GTV-PTV margin.

Prospective Evaluation of the Clinical Benefits of a Novel Tattoo-less Workflow for Nonspine Bone Stereotactic Body Radiation Therapy: Integrating Surface-Guidance With Triggered Imaging Reduces Treatment Time and Eliminates the Need for Tattoos

ObjectiveOligometastatic disease has expanded the indications for non-spine bone stereotactic body radiation therapy (NSB SBRT). We investigated whether optical surface monitoring systems (OSMS) could enable tattoo-less set up and substitute for 2D-3D or cone beam computed tomography (CBCT)-based mid-imaging in NSB SBRT. Materials/MethodsOSMS was incorporated in parallel with an existing workflow using pre-treatment CBCT and mid 2D-3D kV/kV imaging beginning 11/2019. The ability of OSMS to detect out-of-tolerance (>2mm/>2°) and commanded couch shifts was analyzed. A workflow incorporating OSMS reference captures, CBCT for pre-treatment verification and OSMS/triggered imaging (TI) for intrafraction monitoring was developed for rib/sternum SBRT beginning 11/2021 and all NSB SBRT beginning 2/2022. Treatment time and CBCT-related radiation dose between the OSMS and the non-OSMS intrafraction monitoring group was analyzed pre and post-OSMS/TI workflow adoption. All fractions were analyzed through statistical process control (SPC) with use of an XmR chart of treatment time per quarter from 2/2019 to 2/2023. Special cause rules were based on Institute for Healthcare Improvement criteria. ResultsFrom 2/2019 to 2/2023, 1993 NSB SBRT fractions were delivered, including 234 rib, 109 sternum, 214 ilium, and 682 multi-site. Over 20 commanded shifts, OSMS could detect 2mm shifts to within 0.4mm 67% of the time and 0.8mm 95% of time. All NSB SBRT sites showed significant reductions in treatment time, including the greatest improvement in rib total treatment (21.6 to 13.4 minutes, p=1.16*10−17) and beam time (7.9 to 3.2 minutes, p= 7.32*10−27). Significant reductions in CBCT-related radiation were also observed for several NSB sites. These process improvements were associated with OSMS adoption. ConclusionAdoption of a novel NSB SBRT workflow incorporating OSMS/TI for bone intrafraction motion monitoring reduced treatment time and CBCT-related radiation exposure while also allowing for more continuous intrafraction motion monitoring for NSB SBRT. OSMS/TI enabled the transition to a tattoo-less workflow.

Intrafraction Motion and Margin Assessment for Ethos Online Adaptive Radiotherapy Treatments of the Prostate and Seminal Vesicles

IntroductionOnline adaptive radiotherapy (OART) utilizes daily imaging to identify changes in the patient's anatomy and generate a new treatment plan adapted to these changes for each fraction. The aim of this study was to determine the intra-fraction motion and planning target volume (PTV) margins required for an OART workflow on the Varian Ethos system. MethodSixty-five fractions from 13 previously treated OART patients were analyzed for this retrospective study. The prostate and seminal vesicles were contoured by a radiation oncologist on two cone beam computed tomography scans (CBCT) for each fraction; the initial CBCT at the start of the treatment session, and the verification CBCT immediately before beam-on. In part 1 of the study, PTVs of different sizes were defined on the initial CBCT, and the geometric overlap with the clinical target volume (CTV) on the verification CBCT was used to determine the optimal OART margin. This was performed with and without a patient re-alignment shift by registering the verification CBCT to the initial CBCT. In part 2 of the study, the margins determined in part 1 were used for simulated Ethos OART treatments on all 65 fractions. The resultant coverage to the CTV on the verification CBCT, was compared to an image guided radiotherapy (IGRT) workflow with 7mm margins. ResultsPart 1 of the study found, if a verification CBCT and shift is performed, a 4 mm margin on the prostate and 5 mm on the seminal vesicles resulted in 95% of the CTV covered by the PTV in more than 90% of fractions, and 98% of the CTV covered by the PTV in more than 80% of fractions. Part 2 of the study found when these margins were used in an Ethos OART workflow, they resulted in CTV coverage that was superior to an IGRT workflow with 7mm margins. ConclusionA 4 mm prostate margin and 5 mm seminal vesicles margin in an OART workflow with verification imaging are adequate to ensure coverage on the Varian Ethos system. Larger margins may be required if using an OART workflow without verification imaging.

SGRT-based stereotactic body radiotherapy for lung cancer setup accuracy and margin of the PTV.

Surface-guided radiation therapy (SGRT, AlignRT) was used to analyze motion during stereotactic body radiotherapy (SBRT) in lung cancer patients and to explore the margin of the planning target volume (PTV). The residual errors of the AlignRT were evaluated based on grayscale cone-beam computed tomography registration results before each treatment. AlignRT log file was used to analyze the correlation between the frequency and longest duration of errors larger than 2mm and lasting longer than 2 s and maximum error with age and treatment duration. The displacement value at the end of treatment, the average displacement value, and the 95% probability density displacement interval were defined as intrafraction errors, and PTV1, PTV2, PTV3 were calculated by Van Herk formula or Z score analysis. Organ dosimetric differences were compared after the experience-based margin was replaced with PTV3. The interfraction residual errors were Vrt0 , 0.06±0.18cm; Lng0 , -0.03±0.19cm; Lat0 , 0.02±0.15cm; Pitch0 , 0.23±0.7°; Roll0 , 0.1±0.69°; Rtn0 , -0.02±0.79°. The frequency, longest duration and maximum error in vertical direction were correlated with treatment duration (r=0.404, 0.353, 0.283, p<0.05, respectively). In the longitudinal direction, the frequency was correlated with age and treatment duration (r=0.376, 0.283, p<0.05, respectively), maximum error was correlated with age (r=0.4, P<0.05). Vertical, longitudinal, lateral margins of PTV1, PTV2, PTV3 were 2mm, 4mm, 2mm; 2mm, 2mm, 2mm, 3mm, 5mm, 3mm, respectively. After replacing the original PTV, mean lung dose (MLD), 2-cm3 chest wall dose (CD), lung V20 decreased by 0.2Gy, 2.1Gy, 0.5%, respectively (p<0.05). AlignRT can be used for interfraction setup and monitoring intrafraction motion. It is more reasonable to use upper and lower limits of the 95% probability density interval as an intrafraction error.

Clinical Experience of Intrafractional Motion Monitoring of Patients Under Head and Neck Radiation Therapy Using ExacTrac Dynamic System

The combination of surface-guided radiation therapy (SGRT) and image-guided radiation therapy (IGRT) can provide complementary information of patient positioning throughout treatments. The ExacTrac Dynamic (EXTD) system is a combined SGRT and IGRT system that can provide real-time motion detection via optical surface and thermal tracking during treatment delivery, with stereoscopic x-ray for positional verification. The purpose of this study was to examine the performance of EXTD for intrafractional motion monitoring using real clinical cases. Treatment log files exported from EXTD for 40 patients with 335 fractions were retrospectively analyzed. Frequency of beam-hold triggered during treatments were recorded, with the comparison of shifts detected by optical surface tracking (EXTD_Thml) and x-ray verification (EXTD_Xray). Among the 335 fractions, automatic beam-holds were triggered 41 times, followed by x-ray positional verification with internal anatomy. The difference of shifts detected by EXTD_Thml and EXTD_Xray were less than 1 mm and 1° in translational and rotational directions, respectively. After x-ray verification, none of them required the application of positional correction. The availability of x-ray imaging with optical surface tracking in EXTD is essential to verify whether geometric shifts are required to correct patient position. Considering the ability of continuous monitoring of patient positions with optical surface tracking and internal imaging, EXTD is an effective tool for intrafractional motion monitoring during radiation therapy.

Two novel stereotactic radiotherapy methods for locally advanced, previously irradiated head and neck cancers patients

To determine the feasibility and utility of conebeam CT-guided stereotactic radiotherapy for locally recurrent, previously irradiated head and neck cancer (HNC) patients on the Halcyon, a ring delivery system (RDS). This research aims to quantify plan quality, treatment delivery accuracy, and overall efficacy by comparing against novel clinical TrueBeam HyperArc method. Ten recurrent HNC patients who were treated at our institution on TrueBeam (6MV-FFF) for 30 to 40 Gy in 3 to 5 fractions with noncoplanar HyperArc plans were re-planned on Halcyon (6MV-FFF). These plans were re-planned with the same Acuros-based dose engine. Additionally, we used site-specific full/partial coplanar VMAT arcs. PTV coverage, mean dose to GTV, maximum dose to organs-at-risk (OAR), beam-on time (BOT), and quality assurance (QA) results were investigated and compared. Halcyon provided highly conformal HNC SRT plans with slightly superior mean PTVD99 coverage (96.7% vs 95.5%, p = 0.071), and slightly lower mean GTV dose (37.8 Gy vs 38.2 Gy, p = 0.241) when compared to the HyperArc plans. Differences in plan conformality and maximum dose to OARs were statistically insignificant. Due to Halcyon's coplanar geometry, D2cm was significantly higher (p = 0.001) but Halcyon did result in a reduced normal brain dose by 1 Gy on average and up to 5.2 Gy in some cases. Halcyon provided similar patient-specific QA pass rates with a 2%/2mm gamma criteria (98.2% vs 98.5%) and independent in-house Monte Carlo second check results (97.7% vs 98.2%), suggesting identical treatment delivery accuracy. Halcyon plans resulted in slightly longer beam-on time (3.16 vs 2.30 minutes, p = 0.010), however door-to-door patient time is expected to be <10 minutes. Compared to clinical TrueBeam HyperArc, Halcyon SRT plans provided similar plan quality and treatment delivery accuracy with a potentially faster overall treatment using fully automated patient setup and verification. Rapid delivery of recurrent HNC SRT may reduce intrafraction motion errors while also improving patient compliance and comfort. To provide high-quality of HNC SRT similar to HyperArc, we recommend Halcyon users consider commissioning this novel method. This method will be useful for remote and underserved patient cohorts including Halcyon-only clinics as well.

Surface-Guided Radiotherapy: Can We Move on from the Era of Three-Point Markers to the New Era of Thousands of Points?

This literature review covers the basics of SGRT systems and examines whether SGRT can replace the traditional positioning technique. In addition, it investigates SGRT's potential in reducing positioning times, factors affecting SGRT accuracy, the effectiveness of live monitoring, and the impact on patient dosage. This study focused on papers published from 2016 onward that compared SGRT with the traditional positioning technique and investigated factors affecting SGRT accuracy and effectiveness. SGRT provides the same or better results regarding patient positioning. The implementation of SGRT can reduce overall treatment time. It is an effective technique for detecting intrafraction patient motion, improving treatment accuracy and precision, and creating a safe and comfortable environment for the patient during treatment.

Assessment of intrafractional motion of the cervix-uterus by MR-guided radiotherapy system†.

The uterus is known as one of the moving organs. We evaluated the movement of the uterus during irradiation and the effects of changes in the surrounding organs using a magnetic resonance (MR)-guided radiotherapy system. Seven patients with cervical cancer underwent pre- and posttreatment MR imaging to assess changes in the positioning of the uterus and cervix as well as the alterations in bladder and rectal volume. The study revealed that the movements of the uterus were greater than that of the cervix and showed a tendency to correlate with the bladder rather than the rectum. We also examined whether intrafractional motion could lead to insufficient dose coverage of the clinical target volume (CTV), specifically focusing on the D98% of the CTV in the uterine body and cervix. The impact of intrafractional motion on the D98% varied among patients, with one out of the seven patients experiencing an average dosimetric change of -2.6Gy in the uterus, although larger planning target volume margins of 1.5cm were applied, therefore, indicating the need for individualized optimal margins in each case. Online adaptive radiotherapy offers the advantage of modifying the treatment plan when irradiating moving organs, such as the uterus. However, it should be noted that this approach may result in longer overall treatment times compared with the traditional methods. Therefore, we must carefully consider the influence of intrafractional organ motions when opting for such a treatment.

MRI-based inter- and intrafraction motion analysis of the pancreatic tail and spleen as preparation for adaptive MRI-guided radiotherapy in neuroblastoma

BackgroundIn pediatric radiotherapy treatment planning of abdominal tumors, dose constraints to the pancreatic tail/spleen are applied to reduce late toxicity. In this study, an analysis of inter- and intrafraction motion of the pancreatic tail/spleen is performed to estimate the potential benefits of online MRI-guided radiotherapy (MRgRT).Materials and methodsTen randomly selected neuroblastoma patients (median age: 3.4 years), irradiated with intensity-modulated arc therapy at our department (prescription dose: 21.6/1.8 Gy), were retrospectively evaluated for inter- and intrafraction motion of the pancreatic tail/spleen. Three follow-up MRIs (T2- and T1-weighted ± gadolinium) were rigidly registered to a planning CT (pCT), on the vertebrae around the target volume. The pancreatic tail/spleen were delineated on all MRIs and pCT. Interfraction motion was defined as a center of gravity change between pCT and T2-weighted images in left-right (LR), anterior-posterior (AP) and cranial-caudal (CC) direction. For intrafraction motion analysis, organ position on T1-weighted ± gadolinium was compared to T2-weighted. The clinical radiation plan was used to estimate the dose received by the pancreatic tail/spleen for each position.ResultsThe median (IQR) interfraction motion was minimal in LR/AP, and largest in CC direction; pancreatic tail 2.5 mm (8.9), and spleen 0.9 mm (3.9). Intrafraction motion was smaller, but showed a similar motion pattern (pancreatic tail, CC: 0.4 mm (1.6); spleen, CC: 0.9 mm (2.8)). The differences of Dmean associated with inter- and intrafraction motions ranged from − 3.5 to 5.8 Gy for the pancreatic tail and − 1.2 to 3.0 Gy for the spleen. In 6 out of 10 patients, movements of the pancreatic tail and spleen were highlighted as potentially clinically significant because of ≥ 1 Gy dose constraint violation.ConclusionInter- and intrafraction organ motion results into unexpected constrain violations in 60% of a randomly selected neuroblastoma cohort, supporting further prospective exploration of MRgRT.

Experimental comparison of linear regression and LSTM motion prediction models for MLC-tracking on an MRI-linac.

Magnetic resonance imaging (MRI)-guided radiotherapy with multileaf collimator (MLC)-tracking is a promising technique for intra-fractional motion management, achieving high dose conformality without prolonging treatment times. To improve beam-target alignment, the geometric error due to system latency should be reduced by using temporal prediction. To experimentally compare linear regression (LR) and long-short-term memory (LSTM) motion prediction models for MLC-tracking on an MRI-linac using multiple patient-derived traces with different complexities. Experiments were performed on a prototype 1.0T MRI-linac capable of MLC-tracking. A motion phantom was programmed to move a target in superior-inferior (SI) direction according to eight lung cancer patient respiratory motion traces. Target centroid positions were localized from sagittal 2D cine MRIs acquired at 4Hz using a template matching algorithm. The centroid positions were input to one of four motion prediction models. We used (1) a LSTM network which had been optimized in a previous study on patient data from another cohort (offline LSTM). We also used (2) the same LSTM model as a starting point for continuous re-optimization of its weights during the experiment based on recent motion (offline+online LSTM). Furthermore, we implemented (3) a continuously updated LR model, which was solely based on recent motion (online LR). Finally, we used (4) the last available target centroid without any changes as a baseline (no-predictor). The predictions of the models were used to shift the MLC aperture in real-time. An electronic portal imaging device (EPID) was used to visualize the target and MLC aperture during the experiments. Based on the EPID frames, the root-mean-square error (RMSE) between the target and the MLC aperture positions was used to assess the performance of the different motion predictors. Each combination of motion trace and prediction model was repeated twice to test stability, for a total of 64 experiments. The end-to-end latency of the system was measured to be (389 ± 15)ms and was successfully mitigated by both LR and LSTM models. The offline+online LSTM was found to outperform the other models for all investigated motion traces. It obtained a median RMSE over all traces of (2.8 ± 1.3)mm, compared to the (3.2 ± 1.9)mm of the offline LSTM, the (3.3 ± 1.4)mm of the online LR and the (4.4 ± 2.4)mm when using the no-predictor. According to statistical tests, differences were significant (p-value <0.05) among all models in a pair-wise comparison, but for the offline LSTM and online LR pair. The offline+online LSTM was found to be more reproducible than the offline LSTM and the online LR with a maximum deviation in RMSE between two measurements of 10%. This study represents the first experimental comparison of different prediction models for MRI-guided MLC-tracking using several patient-derived respiratory motion traces. We have shown that among the investigated models, continuously re-optimized LSTM networks are the most promising to account for the end-to-end system latency in MRI-guided radiotherapy withMLC-tracking.