The management of respiratory motion in radiation oncology report of AAPM Task Group 76

Clinical experience with free-breathing expiration-gated 10MV FFF VMAT stereotactic lung radiotherapy

BACKGROUND

Free-breathing expiration-gating (EG) is a non-invasive technique used to manage respiratory-induced tumor motion. This study explores the effectiveness of EG stereotactic body radiotherapy (SBRT) for lung tumors using 10MV FFF VMAT.

METHODS AND MATERIALS

The study included 41 patients (50 targets) treated with EG lung SBRT between September 2019 and February 2023. Patients underwent free-breathing uncoached 10-phase 4DCT for planning, with the choice for EG based on e.g. tumor motion, critical organ dose, expected target visibility on free-breathing CBCT, taking into account suitability of the breathing pattern. The gating window was typically set at phases 30-70 % of the breathing cycle. Treatment planning utilized VMAT with 10MV FFF, and tumor motion was monitored using EG-CBCT ± near real-time markerless kV imaging. Treatment times for the different parts of treatment, tumor stability and clinical outcomes were evaluated. Dosimetric outcomes were compared between EG and free-breathing plans for a subset of 10 patients.

RESULTS

EG SBRT substantially reduced longitudinal tumor motion and internal target volume (ITV) by 77 % and 42 % respectively. There was a mean decrease of 21/24 % in V5/V20Gy for the ipsilateral lung. Motion monitoring during treatment for 20 targets showed that intrafraction tumor motion remained within 2 mm for most patients, ensuring accurate dose delivery. 86 % of fractions were completed within 25 min. No local recurrences were observed during a median follow-up of 13 months.

CONCLUSION

Free-breathing EG SBRT is a feasible, effective, and practical approach for lung cancer treatment, offering significant reductions in tumor motion and lung doses while maintaining high treatment accuracy and acceptable treatment times.

Tissue mimicking hydrogel foam materials with mechanical and radiological properties equivalent to human lung

The motion of organs and tissues causes X-ray localization error during radiation therapy. Physical phantoms utilizing materials with tissue-equivalent mechanical and radiological properties are therefore desired to simulate organ motion for radiotherapy optimization. However, the development of such materials is still a challenge. Alginate hydrogel has similar properties to extra cellular matrix, which make it promising for use as a tissue-equivalent material. In this study, alginate hydrogel foams with desired mechanical and radiological properties were synthesized by in-situ release of Ca2+. The air volume ratio was carefully controlled to obtain hydrogel foams tailored to specific mechanical and radiological properties. Both the macroscopic and microscopic morphologies of the materials were characterized, and the compressive behaviors of the hydrogel foams were investigated. Radiological properties were estimated theoretically and validated through CT scanning experiments. This study has elucidated the development of future tissue-equivalent materials, which could be applied for optimization of radiation dosage and quality control during radiotherapy.

A feasibility study of lung tumor segmentation on kilo-voltage radiographic images with transfer learning: Toward tumor motion tracking in radiotherapy

PURPOSE

To segment the lung tumor on kilo-voltage X-ray radiographic images acquired during treatment toward the markerless lung tumor tracking.

METHODS

Per IRB approval, 1150 radiographic images from 80 lung cancer patients were included in the study. We developed a transfer learning deep segmentation net jury committee (TL-DSN-JC) algorithm to segment lung tumors on these images. The proposed models were initialized with the pre-trained VGG-16/19 networks with all but the weights of the connections between the final two layers frozen. A randomized partitioning was applied to train the deep segmentation net. By independently training 12 different deep segmentation nets (DSNs) to form a jury committee (JC), we could determine whether a pixel belonged to the tumor target. Meta-AI Segment Anything Model (SAM) was also tuned to cross-check with our proposed approach.

RESULTS

The results predicted by the TL-DSN-JC algorithm were evaluated using precision, recall, F1 score that is equivalent to the Dice score, and Hausdorff distance (HD). The TL-DSN-JC algorithm outperformed other similar algorithms such as the singular-DSN-without-transfer-learning, the DSN jury committee without transfer learning, and the singular-DSN-with-transfer-learning by up to 80%. Compared to the SAM-based model, the proposed model was superior in terms of HD although similar performance was observed based on the F1/Dice score. The results demonstrated that TL-DSN-JC could segment the tumor with clinically acceptable accuracy.

CONCLUSIONS

The experimental results demonstrated that the proposed algorithm outperformed the conventional deep learning techniques, offering a potential tool for markerless tumor motion tracking on projection images.

Optimization of image reconstruction technique for respiratory-gated lung stereotactic body radiotherapy treatment planning using four-dimensional CT: a phantom study

Patient respiration is characterized by respiratory parameters, such as cycle, amplitude, and baseline drift. In treatment planning using four-dimensional computed tomography (4DCT) images, the target dose may be affected by variations in image reconstruction techniques and respiratory parameters. This study aimed to optimize 4DCT image reconstruction techniques for the treatment planning of lung stereotactic body radiotherapy (SBRT) based on respiratory parameters using respiratory motion phantom. We quantified respiratory parameters using 30 respiratory motion datasets. The 4DCT images were acquired, and the phase- and amplitude-based reconstruction images (RI) were created. The target dose was calculated based on these reconstructed images. Statistical analysis was performed using Pearson's correlation coefficient (r) to determine the relationship between respiratory parameters and target dose in each reconstructed technique and respiratory region. In the inhalation region of phase-based RI, r of the target dose and baseline drift was -0.52. In particular, the target dose was significantly reduced for respiratory parameters with a baseline drift of 0.8 mm/s and above. No other respiratory parameters or respiratory regions were significantly correlated with target dose in phase-based RI. In amplitude-based RI, there were no significant differences in the correlation between all respiratory parameters and target dose in the exhalation or inhalation regions. These results showed that the target dose of the amplitude-based RI did not depend on changes in respiratory parameters or respiratory regions, compared to the phase-based RI. However, it is possible to guarantee the target dose by considering respiratory parameters during the inhalation region of the phase-based RI.

Clinical usefulness of four-dimensional dynamic ventilation CT for borderline resectable locally advanced esophageal cancer

PURPOSE

This study aimed to evaluate the clinical significance of four-dimensional dynamic ventilation CT (4DCT) for assessing resectability in borderline resectable locally advanced esophageal cancer (BR-LAEC) and confirmed the pathological validity of the 4DCT results in surgery without prior treatment.

MATERIALS AND METHODS

We retrospectively reviewed 128 patients (107 men; median age, 68 [range, 43-89] years) diagnosed with BR-LAEC on initial conventional CT (i-CT). These patients were initially classified into three categories: BR1 (closer to resectable), BR2 (resectability not assessable), or BR3 (closer to unresectable). Subsequent 4DCT reclassified patients as either resectable or unresectable within 1 week of i-CT. We analyzed the diagnostic shift induced by 4DCT. Additionally, 18 patients who underwent surgery without prior treatment were evaluated using 4DCT and pathological outcomes.

RESULTS

4DCT reclassified patients with BR-LAEC as resectable (57.0%; 73/128) and unresectable (43.0%; 55/128). Of 53 patients initially classified as BR1, 32.1% (17/53) were reclassified as unresectable, and of 47 patients initially classified as BR3, 46.8% (22/47) were reclassified as resectable. Among 28 patients initially classified as BR2, 53.6% (15/27) were reclassified as resectable and 46.4% (13/27) as unresectable. In the surgery-only cohort of 18 patients, 9 were initially classified as BR1 and 9 as BR2, and all were reclassified as resectable. These patients were pathologically confirmed to have resectable disease.

CONCLUSIONS

4DCT may provide information complementary to that provided by initial conventional CT in assessing resectability among patients with BR-LAEC, and could be a useful adjunct tool for guiding clinical decisions in this patient population.

Predicting early stage lung cancer recurrence and survival from combined tumor motion amplitude and radiomics on free-breathing 4D-CT

BACKGROUND

Cancer control outcomes of lung cancer are hypothesized to be affected by several confounding factors, including tumor heterogeneity and patient history, which have been hypothesized to mitigate the dose delivery effectiveness when treated with radiation therapy. Providing an accurate predictive model to identify patients at risk would enable tailored follow-up strategies during treatment.

PURPOSE

Our goal is to demonstrate the added prognostic value of including tumor displacement amplitude in a predictive model that combines clinical features and computed tomography (CT) radiomics for 2-year recurrence and survival in non-small-cell lung cancer (NSCLC) patients treated with curative-intent stereotactic body radiation therapy.

METHODS

A cohort of 381 patients treated for primary lung cancer with radiotherapy was collected, each including a planning CT with a dosimetry plan, 4D-CT, and clinical information. From this cohort, 101 patients (26.5%) experienced cancer progression (locoregional/distant metastasis) or death within 2 years of the end of treatment. Imaging data was analyzed for radiomics features from the tumor segmented image, as well as tumor motion amplitude measured on 4D-CT. A random forest (RF) model was developed to predict the overall outcomes, which was compared to three other approaches - logistic regression, support vector machine, and convolutional neural networks.

RESULTS

A 6-fold cross-validation study yielded an area under the receiver operating characteristic curve of 72% for progression-free survival when combining clinical data with radiomics features and tumor motion using a RF model (72% sensitivity and 81% specificity). The combined model showed significant improvement compared to standard clinical data. Model performances for loco-regional recurrence and overall survival sub-outcomes were established at 73% and 70%, respectively. No comparative methods reached statistical significance in any data configuration.

CONCLUSIONS

Combined tumor respiratory motion and radiomics features from planning CT showed promising predictive value for 2-year tumor control and survival, indicating the potential need for improving motion management strategies in future studies using machine learning-based prognosis models.

Feasibility study of using next-generation reservoir computing (NG-RC) model to estimate liver tumor motion from external breathing signals

BACKGROUND

Respiratory motion is a challenge for accurate radiotherapy that may be mitigated by real-time tracking. Commercial tracking systems utilize a hybrid external-internal correlation model (ECM), integrating continuous external breathing monitoring with sparse X-ray imaging of the internal tumor position.

PURPOSE

This study investigates the feasibility of using the next generation reservoir computing (NG-RC) model as a hybrid ECM to transform measured external motions into estimated 3D internal motions.

METHODS

The NG-RC model utilizes the nonlinear vector autoregressive (NVAR) machine to account for the hysteresis or phase differences between external and internal motions. The datasets used to evaluate the efficacy of the NG-RC model include 57 motion traces from the CyberKnife system. The datasets were divided into three regions (central, lower, and upper livers) and three motion patterns. These patterns include linear and nonlinear motion patterns (Group A), hysteresis motion patterns (Group B), and all motion patterns (Group C). Moreover, various updating techniques were examined, such as continuously updating the NG-RC model using the first-in-first-out (FIFO) approach and sampling the internal tumor position every 0 s (strategy A), 60 s (strategy B), 30 s (strategy C), and 50 s (strategy D).

RESULTS

The NG-RC model combined with strategy C resulted in better estimation accuracy than the reported CyberKnife cases (Wilcoxon signed rank p < 0.05). For linear and nonlinear motion patterns, the 3D radial estimation accuracy (mean ± SD) using the NG-RC model combined with strategy C and the CyberKnife system was 1.20 ± 0.78 and 1.1 ± 0.20 mm in the central liver, 0.66 ± 0.25 and 1.49 ± 0.50 mm in the lower liver, and 1.73 ± 0.86 and 1.61 ± 0.42 mm in the upper liver. For hysteresis motion patterns, the corresponding values were 1.13 ± 0.37 and 1.45 ± 0.33 mm, 1.43 ± 1.30 and 1.67 ± 0.42 mm, and 1.20 ± 0.68 and 1.46 ± 0.54 mm in the central, lower, and upper livers, respectively.

CONCLUSION

This study proposed a new hybrid correlation model for real-time tumor tracking, which can be used to account for both linear and nonlinear motion patterns, as well as hysteresis motion patterns. Additionally, the NG-RC model required shorter training data sets (15 s) during pre-treatment and short internal motion sampling (every 30 s) during treatment compared to other ECMs.

The effect of kV imaging dose on PTV and OAR planning constraints in lung SBRT using stereoscopic/monoscopic real-time tumor-monitoring system

PURPOSE

Quantify the impact of additional imaging doses on clinical dose constraints during lung stereotactic body radiotherapy (SBRT) treatment utilizing stereoscopic/monoscopic real-time tumor monitoring.

MATERIALS AND METHODS

Thirty lung SBRT patients treated with the volumetric arc therapy technique were randomly selected from the institutional clinical database. Contours of patients' and computed tomography data were extracted from the Eclipse treatment planning system, along with information regarding the treatment dose. Subsequently, patient-specific three-dimensional real-time imaging dose distributions were computed using a validated Monte Carlo simulation of the ExacTrac imaging. The 3D imaging dose was added to the treatment dose, and the influence of the imaging dose on clinical dose constraints was analyzed for planning target volume (PTV) and various organs at risk (OARs).

RESULTS

Among the 30 patients, 14 patients exhibited one or more failed OAR constraints based solely on the treatment dose, resulting in a total of 24 constraint failures. The addition of the real-time imaging dose altered the pass/fail criteria for one OAR constraint and two PTV constraints. The change in constraint due to additional imaging dose relative to the prescription dose was less than 1% for all patients, except for one case, where it reached 1.9%, which had remained below the threshold of 5% recommended by AAPM TG-180 guidelines. Furthermore, the additional imaging dose relative to the treatment dose resulted in an increase in OAR constraints ranging from 0 to 27% (mean of 0.8%), with nine cases exceeding 5%.

CONCLUSION

The current study represents the first attempt to investigate the impact of additional imaging doses on clinical planning constraints in real-time tumor monitoring during lung SBRT utilizing ExacTrac imaging system. The addition of an imaging dose will likely have minimal clinical impact.

Commissioning of a motion management system for a 1.5T Elekta Unity MR-Linac: A single institution experience

PURPOSE

This work describes a single institution experience of commissioning a real-time target tracking and beam control system, known as comprehensive motion management, for a 1.5 T Elekta MR-Linac.

METHODS

Anatomical tracking and radiation beam control were tested using the MRI4D Quasar motion phantom. Multiple respiratory breathing traces were modeled across a range of realistic regular and irregular breathing patterns ranging between 10 and 18 breaths per minute. Each of the breathing traces was used to characterize the anatomical position monitoring (APM) accuracy, and beam latency, and to quantify the dosimetric impact of both parameters during a respiratory-gated delivery using EBT3 film dosimetry. Additional commissioning tasks were performed to verify the dosimetric constancy during beam gating and to expand our existing quality assurance program.

RESULTS

It was determined that APM correctly predicted the 3D position of a dynamically moving tracking target to within 1.5 mm for 95% of the imaging frames with no deviation exceeding 2 mm. Among the breathing traces investigated, the mean latency ranged between -21.7 and 7.9 ms with 95% of all observed latencies within 188.3 ms. No discernable differences were observed in the relative profiles or cumulative output for a gated beam relative to an ungated beam with minimal dosimetric impact observed due to system latency. Measured dose profiles for all gated scenarios retained a gamma pass rate of 97% or higher for a 3%/2 mm criteria relative to a theoretical gated dose profile without latency or tracking inaccuracies.

CONCLUSION

MRI-guided target tracking and automated beam delivery control were successfully commissioned for the Elekta Unity MR-Linac. These gating features were shown to be highly accurate with an effectively small beam latency for a range of regular and irregular respiratory breathing traces.

The volumetric and dosimetric impacts of respiratory motion management in lung SBRT: A systematic review from 2019-2024

BACKGROUND

The efficacy of Stereotactic Body Radiation Therapy (SBRT) is contingent upon accurately accounting for respiratory motion. Although several methods have been developed, the extent of volumetric and dosimetric benefit, as well as the criteria for selecting appropriate methods for individual patients remain unclear.

PURPOSE

To assess the extent of target volume reduction and lung dose reduction in lung cancer patients treated with SBRT, comparing active versus non-active respiratory motion management approaches.

MATERIALS AND METHODS

A comprehensive search was conducted across multiple databases, including MEDLINE Ovid (PubMed), EMBASE, and the Web of Science Core Collection, covering the period from 2019 to 2024. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed to identify studies relevant to respiratory motion management in lung SBRT. Data extracted included target volume delineation, target volume sizes, and lung doses reported.

RESULTS

The review included 14 studies involving 273 patients, which examined both active and non-active respiratory motion management approaches. Active respiratory motion management approaches were associated with significant reduced target volume sizes and lung doses compared to non-active approaches. Tracking and deep inspiration breath-hold demonstrated superiority in reduction in target volume and lung protection, with tracking showing the greatest reduction in target volume.

CONCLUSION

Patient selection is crucial when determining the most appropriate respiratory motion management approach. Establishing a consensus on planning objective is necessary for accurate data evaluation. Further research is required to refine these techniques and explore innovative technologies that could enhance the effectiveness and safety of respiratory motion management in lung SBRT.

A Retrospective Analysis of the First Clinical 5DCT Workflow

BACKGROUND/OBJECTIVES

5DCT was first proposed in 2005 as a motion-compensated CT simulation approach for radiotherapy treatment planning to avoid sorting artifacts that arise in 4DCT when patients breathe irregularly. Since March 2019, 5DCT has been clinically implemented for routine use at our institution to leverage this technological advantage. The clinical workflow includes a quality assurance report that describes the output of primary workflow steps. This study reports on the challenges and quality of the clinical 5DCT workflow using these quality assurance reports.

METHODS

We evaluated all thoracic 5DCT simulation datasets consecutively acquired at our institution between March 2019 and December 2022 for thoracic radiotherapy treatment planning. The 5DCT datasets utilized motion models constructed from 25 fast-helical free-breathing computed tomography (FHFBCTs) with simultaneous respiratory bellows signal monitoring to reconstruct individual, user-specified breathing-phase images (termed 5DCT phase images) for internal target volume contouring. Each 5DCT dataset was accompanied by a structured quality assurance report composed of qualitative and quantitative measures of the breathing pattern, image quality, DIR quality, model fitting accuracy, and a validation process by which the original FHFBCT scans were regenerated with the 5DCT model. Measures of breathing irregularity, image quality, and DIR quality were retrospectively categorized on a grading scale from 1 (regular breathing and accurate registration/modeling) to 4 (irregular breathing and inaccurate registration/modeling). The validation process was graded according to the same scale, and this grade was termed the suitability-for-treatment-planning (STP) grade. We correlated the graded variables to the STP grade. In addition to the quality assurance reports, we reviewed the contour sessions to determine how often 5DCT phase images were used for treatment planning and delivery.

RESULTS

There were 169 5DCT simulation datasets available from 156 patients for analysis. The STP was moderately correlated with breathing irregularity, image quality, and DIR quality (Spearman coefficients: 0.26, 0.30, and 0.50, respectively). Multiple linear regression analysis demonstrated that STP was correlated with regular breathing patterns (p = 0.008), image quality (p < 0.001), and better DIR quality (p < 0.001). 5DCT datasets were used for treatment planning in 82% of cases, while in 12% of cases, a backup image process was used. In total, 6% of image datasets were not used for treatment planning due to factors unrelated to the 5DCT workflow quality.

CONCLUSIONS

The strongest association with STP was with DIR quality grades, as indicated by both Spearman and multiple linear regression analysis, implying that improvements to DIR accuracy and evaluation may be the best route for further improvement to 5DCT. The high rate of 5DCT phase image use for treatment planning showed that the workflow was reliable, and this has encouraged us to continue to develop and improve the workflow steps.

Recent developments in the field of radiotherapy for the management of lung cancer

Lung cancer has a poor prognosis, and further improvements in outcomes are needed. Radiotherapy plays an important role in the treatment of unresectable lung cancer, and there have been recent developments in the field of radiotherapy for the management of lung cancer. However, to date, there have been few reviews on the improvement in treatment outcomes associated with high precision radiotherapy for lung cancer. Thus, this review aimed to summarize the recent developments in radiotherapy techniques and indicate the future directions in the use of radiotherapy for lung cancer. Stereotactic body radiotherapy (SBRT) for unresectable stage I lung cancer has been reported to improve local control rates without severe adverse events, such as radiation pneumonitis. For locally advanced lung cancer, a combination of chemoradiotherapy and adjuvant immune checkpoint inhibitors dramatically improves treatment outcomes, and intensity-modulated radiotherapy (IMRT) enables safer radiation therapy with less frequent pneumonitis. Particle beam therapy, such as carbon-ion radiotherapy and proton beam therapy, has been administered as advanced medical care for patients with lung cancer. Since 2024, it has been covered under insurance for early stage lung cancer with tumors ≤ 5 cm in size in Japan. In addition to chemotherapy, local ablative radiotherapy improves treatment outcomes in patients with oligometastatic stage IV lung cancer. A particular problem with radiotherapy for lung cancer is that the target location changes with respiratory motion, and various physical methods have been used to control respiratory motion. Recently, coronavirus disease has had a major impact on lung cancer treatment, and cancer treatment during situations, such as the coronavirus pandemic, must be performed carefully. To improve treatment outcomes for lung cancer, it is necessary to fully utilize evolving radiotherapy modalities, and the role of radiotherapy in lung cancer treatment is expected to increase.

Imaging lung tumor motion using integrated-mode proton radiography-A phantom study towards tumor tracking in proton radiotherapy

BACKGROUND

Motion of lung tumors during radiotherapy leads to decreased accuracy of the delivered dose distribution. This is especially true for proton radiotherapy due to the finite range of the proton beam. Methods for mitigating motion rely on knowing the position of the tumor during treatment.

PURPOSE

Proton radiography uses the treatment beam, at an energy high enough to traverse the patient, to produce a radiograph. This work shows the first results of using an integrated-mode proton radiography system to track the position of moving objects in an experimental phantom study; demonstrating the potential of using this method for measuring tumor motion.

METHODS

Proton radiographs of an anthropomorphic lung phantom, with a motor-driven tumor insert, were acquired approximately every 1 s, using tumor inserts of 10, 20, and 30 mm undergoing a known periodic motion. The proton radiography system used a monolithic scintillator block and digital cameras to capture the residual range of each pencil beam passing through the phantom. These ranges were then used to produce a water equivalent thickness map of the phantom. The centroid of the tumor insert in the radiographs was used to determine its position. This measured position was then compared to the known motion of the phantom to determine the accuracy.

RESULTS

Submillimeter accuracy on the measurement of the tumor insert was achieved when using a 30 mm tumor insert with a period of 24 s and was found to be improved for decreasing motion amplitudes with a mean absolute error (MAE) of 1.0, 0.9, and 0.7 mm for 20, 15, and 10 mm respectively. Using smaller tumor inserts reduced the accuracy with a MAE of 1.8 and 1.9 mm for a 20 and 10 mm insert respectively undergoing a periodic motion with an amplitude of 20 mm and a period of 24 s. Using a shorter period resulted in significant motion artifacts reducing the accuracy to a MAE of 2.2 mm for a 12 s period and 3.1 mm for a 6 s period for the 30 mm insert with an amplitude of 20 mm.

CONCLUSIONS

This work demonstrates that the position of a lung tumor insert in a realistic anthropomorphic phantom can be measured with high accuracy using proton radiographs. Results show that the accuracy of the position measurement is the highest for slower tumor motions due to a reduction in motion artifacts. This indicates that the primary obstacle to accurate measurement is the speed of the radiograph acquisition. Although the slower tumor motions used in this study are not clinically realistic, this work demonstrates the potential for using proton radiography for measuring tumor motion with an increased scanning speed that results in a decreased acquisition time.

Fluence smoothing evaluation for whole-breast automatically generated treatment plans

PURPOSE

This study aimed to identify the fluence smoothing threshold that preserves the dosimetric quality of planning for breast cancer intensity-modulated radiation therapy (IMRT).

MATERIAL AND METHODS

We conducted automated treatment planning for 60 breast cancer patients using the Eclipse Scripting Application Programming Interface. The plans included four-field IMRT, emphasizing smoothing weight combinations while maintaining a 4:3 aspect ratio between the X and Y directions. Four weight sets (40 × 30, 100 × 75, 150 × 115.2, and 200 × 150) were tested, resulting in four plans per patient. A total dose of 40.05 Gy over 15 fractions was prescribed. Optimization weigths were dynamically adjusted based on dosimetric evaluations, with the maximum coverage priority set at 200. Statistical analyses were used to assess the dosimetric data.

RESULTS

The median planning target volume (PTV) coverage varied across smoothing levels, with default smoothing (40 × 30) providing superior median PTV coverage. Lung constraints showed significant differences mainly at higher smoothing levels. Heart constraints exhibited less variation between smoothing levels, with significant differences primarily in the maximum and mean doses for right-sided patients and between default and higher smoothing levels for left-sided patients. No significant differences were observed in contralateral breast constraints among all smoothing levels, except at the maximum level for right-sided patients. Monitor units decreased with increasing smoothing weight, showing significant differences between default and other settings. For right-sided patients, the median number of monitor units varied from 1346 (40 × 30) to 754 (200 × 150), and for left-sided patients, from 1333 (40 × 30) to 804 (200 × 150). Chi-square tests revealed differences in dose constraint adherence between default and maximum smoothing levels, particularly in target coverage.

CONCLUSION

Our findings suggest that using a ratio of smoothing weights to target priorities between 1:1.5 and 1:1.6 leads to a favorable balance between complexity and dosimetric plan quality, with no significant impacts on dose constraint adherence.

Multi-Institutional Phase II Study on the Efficacy and Safety of Dynamic Tumor-Tracking, Moderately Hypofractionated Intensity-Modulated Radiotherapy in Patients With Locally Advanced Pancreatic Cancer

BACKGROUND

For delivering high radiation doses to pancreatic tumors, organ motion management is indispensable; however, studies on this are limited. We aimed to evaluate the efficacy and safety of dynamic tumor tracking (DTT) moderately hypofractionated intensity-modulated radiotherapy (IMRT) in patients with locally advanced pancreatic cancer (LAPC).

METHODS

Patients with histological confirmation for LAPC were included. A linac system, which was mounted with a gimbal function, was used for DTT-IMRT. The prescribed dose was 48 Gy in 15 fractions. The primary endpoint was the 1-year rate of freedom from locoregional progression (FFLP).

RESULTS

DTT-IMRT was successfully administered in 25 patients enrolled from four institutions. The median range of respiratory motion during DTT-IMRT was 9.8 mm (range: 3.5-27.3 mm), and the median tracking accuracy was 2.6 mm (range: 0.7-5.2 mm). With a median follow-up period of 13.9 months, the 1-year FFLP rate was 75.3% (lower limit of one-sided 80% confidence interval [CI]: 60.2%), which satisfied the predetermined primary endpoint. One-year locoregional progression-free survival, progression-free survival, and overall survival were 56.0% (95% CI: 34.8%-72.7%), 44.0% (95% CI: 24.5%-61.9%), and 60.0% (95% CI: 38.4%-76.1%), respectively. Regarding nonhematologic toxicities, grade 3 acute gastrointestinal (GI) toxicity was observed in two patients (8%), and two patients (8%) each experienced grade 3 late GI and non-GI toxicities. No grade 4 or 5 nonhematologic toxicities were observed.

CONCLUSIONS

DTT moderately hypofractionated IMRT shows preferable locoregional control without significant toxicity in patients with LAPC.

TRIAL REGISTRATION

UMIN000017521.

Noninvasive Mechanical Ventilation Is a Promising Way to Improve Lung Cancer Radiation Therapy

Purpose

Accurate radiation therapy (RT) for lung cancer is challenging because of the respiratory motion of the tumor and surrounding organs at risk. Recently, non-invasive mechanical ventilation (NIMV) has been investigated as a novel respiratory motion management strategy. Using NIMV, respiratory motion can be minimized, while a larger lung volume yields less overall lung dose. The purpose of this study was to determine the potential benefit of NIMV to improve lung cancer RT using magnetic resonance imaging (MRI) data of healthy volunteers.

Methods and Materials

Twelve healthy volunteers practiced NIMV at 60 breaths per minute (NIMV60) with added positive end-expiratory pressure (PEEP) in 2 sessions and subsequently underwent NIMV60 in 2 MRI sessions. We acquired single-slice sagittal 2-dimensional MRI images at 2.6 Hz for 6 minutes during free breathing and NIMV60. We quantified the motion of all visible cross-sections of lung arteries, as a surrogate for lung tumors, in cranio-caudal and anterior-posterior directions using deformable image registration, distinguishing between 4 quadrants in the lungs (posterior-cranial, posterior-caudal, anterior-caudal, and anterior-cranial). Also, we analyzed average lung area, as a surrogate for lung volume, on the sagittal images using automatic segmentation.

Results

All volunteers were successfully trained to be ventilated with NIMV60, and completed all sessions. The reduction of the median lung artery motion in each of the quadrants varied from 61% to 67% (from 10.7-29.9 to 3.8-11.7 mm) in cranio-caudal direction and from 51% to 68% (from 8.0-13.7 to 3.0-5.1 mm) in anterior-posterior direction using NIMV60. NIMV60 increased the sagittal lung area by 35% compared with free breathing.

Conclusions

NIMV60 with added PEEP is a promising way to improve lung cancer RT because of reduced respiratory motion and increased lung area compared with free breathing.

Proton therapy of lung cancer patients - Treatment strategies and clinical experience from a medical physicist's perspective

PURPOSE

Proton therapy of moving targets is considered a challenge. At Maastro, we started treating lung cancer patients with proton therapy in October 2019. In this work, we summarise the developed treatment strategies and gained clinical experience from a physics point of view.

METHODS

We report on our clinical approaches to treat lung cancer patients with the Mevion Hyperscan S250i proton machine. We classify lung cancer patients as small movers (tumour movement ≤ 5 mm) or large movers (tumour movement > 5 mm). The preferred beam configuration has evolved over the years of clinical treatment, and currently mostly two or three beam directions are used. All patients are treated with robustly optimised plans (5 mm setup and 3% range uncertainty). Small movers are planned based on a clinical target volume (CTV) with a 3 mm isotropic margin expansion to account for motion, while large movers are planned based on an internal target volume (ITV). All patients are treated in free-breathing.

RESULTS

Between October 2019 and December 2023, 379 lung cancer patients have been treated, of which 130 were large movers. The adaptation rate was 28%. The median treatment time has been reduced from 30 to 23 min. The mean dose to the heart, oesophagus, and lungs was on average 4.3, 15.4, and 11.0 Gy, respectively.

CONCLUSIONS

Several treatment planning and workflow improvements have been introduced over the years, resulting in an increase of treatment quality and number of treated patients, as well as reduction of planning and treatment time.

Investigating the effects of table movement and sag on optical surrogate-driven respiratory-guided computed tomography

PURPOSE

Respiratory-guided computed tomography (CT) typically employs breathing motion surrogates to feed image reconstruction or visual breathing coaching. Our study aimed to assess the impact of table movements and table sag on the breathing curves recorded in four-dimensional (4D) CT and deep-inspiration breath-hold (DIBH) CT.

METHODS

For breathing curve measurements, static and dynamic phantom scenarios were used. Breathing curves were recorded using three different surrogate systems and the impact of table sag due to weights of up to 130 kg was analyzed and compared to a non-weighted setting, respectively. The calibration procedure of the system used as an input for the visual coaching device used for clinical DIBH CT scans was adapted. We evaluated corresponding breathing curves acquired during DIBH and 4DCT scans of altogether 70 patients using various stability metrics.

RESULTS

The various surrogate systems showed consistent table sag measurements below 4 mm, even under loads up to 130 kg, compared to a reference scan conducted without additional weight. Higher weight loads were related to steeper table sag fall-offs towards the deepest table position. For DIBH CT scans, the visual guidance was heavily affected by artifacts. This resulted in breathing threshold limits, which could not be achieved by 48% (n = 21) of the, respectively, examined patients. Using the new calibration workflow, the baseline drift was compensated better and 90% (n = 20) of the addressed patients stayed within the thresholds. The evaluated table sag in clinical 4DCT scans (n = 29) stayed below 3 mm compared to the non-weighted situation.

CONCLUSION

Table movement and sag can impact breathing curves recorded by different surrogate systems. Correcting table movement and sag artifacts is crucial for reliable breathing curve acquisition in respiratory-guided CT.

Real-time CBCT imaging and motion tracking via a single arbitrarily-angled x-ray projection by a joint dynamic reconstruction and motion estimation (DREME) framework

Objective.Real-time cone-beam computed tomography (CBCT) provides instantaneous visualization of patient anatomy for image guidance, motion tracking, and online treatment adaptation in radiotherapy. While many real-time imaging and motion tracking methods leveraged patient-specific prior information to alleviate under-sampling challenges and meet the temporal constraint (<500 ms), the prior information can be outdated and introduce biases, thus compromising the imaging and motion tracking accuracy. To address this challenge, we developed a frameworkdynamicreconstruction andmotionestimation (DREME) for real-time CBCT imaging and motion estimation, without relying on patient-specific prior knowledge.Approach.DREME incorporates a deep learning-based real-time CBCT imaging and motion estimation method into a dynamic CBCT reconstruction framework. The reconstruction framework reconstructs a dynamic sequence of CBCTs in a data-driven manner from a standard pre-treatment scan, without requiring patient-specific prior knowledge. Meanwhile, a convolutional neural network-based motion encoder is jointly trained during the reconstruction to learn motion-related features relevant for real-time motion estimation, based on a single arbitrarily-angled x-ray projection. DREME was tested on digital phantom simulations and real patient studies.Main Results.DREME accurately solved 3D respiration-induced anatomical motion in real time (∼1.5 ms inference time for each x-ray projection). For the digital phantom studies, it achieved an average lung tumor center-of-mass localization error of 1.2 ± 0.9 mm (Mean ± SD). For the patient studies, it achieved a real-time tumor localization accuracy of 1.6 ± 1.6 mm in the projection domain.Significance.DREME achieves CBCT and volumetric motion estimation in real time from a single x-ray projection at arbitrary angles, paving the way for future clinical applications in intra-fractional motion management. In addition, it can be used for dose tracking and treatment assessment, when combined with real-time dose calculation.

Dose-Escalated SBRT for Borderline and Locally Advanced Pancreatic Cancer: Resectability Rate and Pathological Results of a Multicenter Prospective Study

OBJECTIVE

We demonstrated for the first time the safety and feasibility of escalating up to 55 Gy/11 Gy/fr/5fr in borderline (BRPC)/unresectable locally advanced pancreatic cancer (LAPC), using the standard LINAC platform. The aim of the present study is to assess for the first time the impact of this high-dose neoadjuvant stereotactic ablative radiotherapy (SABRT) protocol on tumor resectability and pathological responses.

MATERIALS/METHODS

From June 2017 to December 2022, patients with BRPC/LAPC were treated with neoadjuvant chemotherapy (ChT) and SABRT-escalated doses of SIB at 45 Gy, 50 Gy, and up to 55 Gy (BED ≥ 100). Radiological evaluation was conducted with a CT scan 6-8 weeks post-treatment to determine resectability status based on established criteria (SAR/APA2014). Surgical decisions were made by the multidisciplinary tumor board of the participating institutions. Pathological assessments post-surgery used criteria from the College of American Pathologists (CAP), categorizing resection status as R0 (negative margins), R1 (microscopic tumor margins), and R2 (macroscopic tumor margins). Tumor response was evaluated with the Tumor Response Scoring (TRS) system, as G0 (no viable cancer cells), G1 (single cells or rare small groups), G2 (residual cancer with evident regression), and G3 (extensive residual cancer).

RESULTS

Thirty-three patients (p) were included: 39.4% (13p) BRPC/60.6% (20p) LAPC. After ChT-SABRT, 45.5% (15p) were considered resectable, with 11/13 (84.6%) BRPC and 4/20 (20%) LAPC (p < 0.0001). One patient refused surgery and other patient died of COVID sepsis. Two more patients had disseminated disease at surgery. Among the 11 patients who underwent full surgery, all patients achieved either clean margins R0: 72.7% (8p) or microscopic affected margins R1: 27.3% (3p). TRS scores were G1: 27.3% (3p), G2: 54.5% (6p), and G3: 18.2% (2p). The present follow-up (FUP) was closed on 1 November 2024 (23.55 months, range: 6-71 months). The mean freedom from local progression as the first cause of disease failure was 43.30 ± 3.09 (37.23-49.38), and the median was not reached. The actuarial 1- and 2-year rates for freedom from local relapse as a first cause of disease failure were 92.3% (87.7-93.3%) and 79.7% (79.7-87.7%), respectively.

CONCLUSIONS

Neoadjuvant ChT-SABRT in LAPC improves resectability rates and induces relevant tumor regression. These promising findings should be validated by larger sample sizes and extended follow-up.

Effectiveness of 4-dimensional maximum intensity projection (4D-MIP) for respiratory motion management with uncertain interobserver delineation

This study was conducted to evaluate the use of 4-dimensional (4D) maximum intensity projection (4D-MIP) to compensate for the disadvantages of average intensity projection (AIP), which is used to determine the internal target volume (ITV) in lung tumors. A respiratory motion phantom with a simulated tumor was imaged using 4D computed tomography (4D-CT). AIP and 4D-MIP were generated based on 10 phases of 4D-CT, followed by contouring of the ITVAIP and ITVMIP; these were compared with the ITV contoured in 10 phases of 4D-CT (ITV10). Additionally, the profile curves of the ITVAIP and ITVMIP were obtained, and the full width at half maximum (FWHM) was measured. There was no significant difference between the ITV10 and ITVMIP; however, the ITVAIP demonstrated a lower value. The FWHM values of the ITVAIP were smaller than those of ITVMIP owing to decreased CT values in the superior-inferior margin. 4D-MIP may contribute to improving the consistency of the ITV delineation.

Proton Beam Therapy for Pancreatic Tumors: A Consensus Statement from the Particle Therapy Cooperative Group Gastrointestinal Subcommittee

Radiation therapy manages pancreatic cancer in various settings; however, the proximity of gastrointestinal (GI) luminal organs at risk (OARs) poses challenges to conventional radiation therapy. Proton beam therapy (PBT) may reduce toxicities compared to photon therapy. This consensus statement summarizes PBT's safe and optimal delivery for pancreatic tumors. Our group has specific expertise using PBT for GI indications and has developed expert recommendations for treating pancreatic tumors with PBT. Computed tomography (CT) simulation: Patients should be simulated supine (arms above head) with custom upper body immobilization. For stomach/duodenum filling consistency, patients should restrict oral intake within 3 hours before simulation/treatments. Fiducial markers may be implanted for image guidance; however, their design and composition require scrutiny. The reconstruction field-of-view should encompass all immobilization devices at the target level (CT slice thickness 2-3 mm). Four-dimensional CT should quantify respiratory motion and guide motion mitigation. Respiratory gating is recommended when motion affects OAR sparing or reduces target coverage. Treatment planning: Beam-angle selection factors include priority OAR-dose minimization, water-equivalent-thickness stability along the beam path, and enhanced relative biological effect consideration due to the increased linear energy transfer at the proton beam end-of-range. Posterior and right-lateral beam angles that avoid traversing GI luminal structures are preferred (minimizing dosimetric impacts of variable anatomies). Pencil beam scanning techniques should use robust optimization. Single-field optimization is preferable to increase robustness, but if OAR constraints cannot be met, multifield optimization may be used. Treatment delivery: Volumetric image guidance should be used daily. CT scans should be acquired ad hoc as necessary (at minimum every other week) to assess the dosimetric impacts of anatomy changes. Adaptive replanning should be performed as required. Our group has developed recommendations for delivering PBT to safely and effectively manage pancreatic tumors.

Super-resolution reconstruction of time-resolved four-dimensional computed tomography (TR-4DCT) with multiple breathing cycles based on TR-4DMRI

BACKGROUND

Respiratory motion irregularities in lung cancer patients are common and can be severe during multi-fractional (∼20 mins/fraction) radiotherapy. However, the current clinical standard of motion management is to use a single-breath respiratory-correlated four-dimension computed tomography (RC-4DCT or 4DCT) to estimate tumor motion to delineate the internal tumor volume (ITV), covering the trajectory of tumor motion, as a treatment target.

PURPOSE

To develop a novel multi-breath time-resolved (TR) 4DCT using the super-resolution reconstruction framework with TR 4D magnetic resonance imaging (TR-4DMRI) as guidance for patient-specific breathing irregularity assessment, overcoming the shortcomings of RC-4DCT, including binning artifacts and single-breath limitations.

METHODS

Six lung cancer patients participated in the IRB-approved protocol study to receive multiple T1w MRI scans, besides an RC-4DCT scan on the simulation day, including 80 low-resolution (lowR: 5 × 5 × 5 mm3) free-breathing (FB) 3D cine MRFB images in 40 s (2 Hz) and a high-resolution (highR: 2 × 2 × 2 mm3) 3D breath-hold (BH) MRBH image for each patient. A CT (1 × 1 × 3 mm3) image was selected from 10-bin RC-4DCT with minimal binning artifacts and a close diaphragm match (<1 cm) to the MRBH image. A mutual-information-based Freeform deformable image registration (DIR) was used to register the CT and MRBH via the opposite directions (namely F1:C T Source → MR Target BH ${\mathrm{C}}{{{\mathrm{T}}}_{{\mathrm{Source}}}} \to {\mathrm{MR}}_{{\mathrm{Target}}}^{{\mathrm{BH}}}$ and F2:C T Target ← MR Source BH ${\mathrm{C}}{{{\mathrm{T}}}_{{\mathrm{Target}}}} \leftarrow {\mathrm{MR}}_{{\mathrm{Source}}}^{{\mathrm{BH}}}$ ) to establish CT-MR voxel correspondences. An intensity-based enhanced Demons DIR was then applied forMR Source BH → MR Target FB ${\mathrm{MR}}_{{\mathrm{Source}}}^{{\mathrm{BH}}} \to {\mathrm{MR}}_{{\mathrm{Target}}}^{{\mathrm{FB}}}$ , in which the original MRBH was used in D1:C T Source → ( MR Source BH → MR Target FB ) Target ${\mathrm{C}}{{{\mathrm{T}}}_{{\mathrm{Source}}}} \to {{({\mathrm{MR}}_{{\mathrm{Source}}}^{{\mathrm{BH}}} \to {\mathrm{MR}}_{{\mathrm{Target}}}^{{\mathrm{FB}}})}_{{\mathrm{Target}}}}$ , while the deformed MRBH was used in D2:( C T Target ← MR Source BH ) Source → MR Target FB ${{( \text{C}{{\text{T}}_{\text{Target}}}\leftarrow \text{MR}_{\text{Source}}^{\text{BH}} )}_{\text{Source}}}\to \text{MR}_{\text{Target}}^{\text{FB}}$ . The deformation vector fields (DVFs) obtained from each DIR were composed to apply to the deformed CT (D1) and original CT (D2) to reconstruct TR-4DCT images. A digital 4D-XCAT phantom at the end of inhalation (EOI) and end of exhalation (EOE) with 2.5 cm diaphragmatic motion and three spherical targets (ϕ = 2, 3, 4 cm) were first tested to reconstruct TR-4DCT. For each of the six patients, TR-4DCT images at the EOI, middle (MID), and EOE were reconstructed with both D1 and D2 approaches. TR-4DCT image quality was evaluated with mean distance-to-agreement (MDA) at the diaphragm compared with MRFB, tumor volume ratio (TVR) referenced to MRBH, and tumor shape difference (DICE index) compared with the selected input CT. Additionally, differences in the tumor center of mass (|∆COMD1-D2|), together with TVR and DICE comparison, was assessed in the D1 and D2 reconstructed TR-4DCT images.

RESULTS

In the phantom, TR-4DCT quality is assessed by MDA = 2.0 ± 0.8 mm at the diaphragm, TVR = 0.8 ± 0.0 for all tumors, and DICE = 0.83 ± 0.01, 0.85 ± 0.02, 0.88 ± 0.01 for ϕ = 2, 3, 4 cm tumors, respectively. In six patients, the MDA in diaphragm match is -1.6 ± 3.1 mm (D1) and 1.0 ± 3.9 mm (D2) between the reconstructed TR-4DCT and lowR MRFB among 18 images (3 phases/patient). The tumor similarity is TVR = 1.2 ± 0.2 and DICE = 0.70 ± 0.07 for D1 and TVR = 1.4 ± 0.3 (D2) and DICE = 0.73 ± 0.07 for D2. The tumor position difference is |∆COMD1-D2| = 1.2 ± 0.8 mm between D1 and D2 reconstructions.

CONCLUSION

The feasibility of super-resolution reconstruction of multi-breathing-cycle TR-4DCT is demonstrated and image quality at the diaphragm and tumor is assessed in both the 4D-XCAT phantom and six lung cancer patients. The similarity of D1 and D2 reconstruction suggests consistent and reliable DIR results. Clinically, TR-4DCT has the potential for breathing irregularity assessment and dosimetry evaluation in radiotherapy.

Impact of diaphragm motion on dosimetry in lower thoracic spine stereotactic body radiotherapy

BACKGROUND AND PURPOSE

Free-breathing computed tomography (FBCT) used in treatment planning for lower thoracic (Th8-Th12) spine stereotactic body radiotherapy (SBRT) can cause deviations between planned and irradiated doses due to diaphragm movement (DM). This study analyzed the dosimetric impact of DM on lower thoracic spine SBRT.

MATERIALS AND METHODS

Data were collected from 19 patients who underwent FBCT and four-dimensional CT (4DCT) during the same session. The 4DCT data were divided into ten respiratory phases (0-90%), and an average CT (AveCT) was reconstructed from them. Using FBCT, target and normal tissues near the diaphragm were contoured and spine SBRT plans with 24-Gy doses in two fractions were created. These plans were applied to each phase of CT and AveCT, with doses recalculated using the same parameters. Actual treatment doses (Deformed AveCT) were estimated by accumulating doses across each 4DCT phase using deformable image registration on the AveCT. Dose-volume histogram (DVH) indices were compared between the FBCT, AveCT, 0% phase, 50% phase, and Deformed AveCT plans.

RESULTS

The mean differences in DVH indices for target and normal tissues were within 2.4 and 2.1%, respectively, when the diaphragm displacement was between -1.6 cm and 2.0 cm, as compared with FBCT. DM displacement showed moderate to strong correlations with DVH differences.

CONCLUSION

Our results indicate that DM has a minor impact on DVH indices if the diaphragm remains within 1.5 cm of the FBCT position.

AAPM task group report 135.B: Quality assurance for robotic radiosurgery

AAPM Task Group Report 135.B covers new technology components that have been added to an established radiosurgery platform and updates the components that were not well covered in the previous report. Considering the current state of the platform, this task group (TG) is a combination of a foundational task group to establish the basis for new processes/technology and an educational task group updating guidelines on the established components of the platform. Because the technology discussed in this document has a relatively small user base compared to C-arm isocentric linacs, the authors chose to emphasize the educational components to assist medical physicists who are new to the technology and have not had the opportunity to receive in-depth vendor training at the time of reading this report. The TG has developed codes of practice, introduced QA, and developed guidelines which are generally expected to become enduring practice. This report makes prescriptive recommendations as there has not been enough longitudinal experience with some of the new technical components to develop a data-based risk analysis.

Margins to compensate for respiratory-induced mismatches between lung tumor and fiducial marker positions using four-dimensional computed tomography

Background and purpose

Tumors and fiducial markers do not always exhibit synchronous motion across different respiratory phases, in a phenomenon called the target localization error (TLE). We determined the margin to compensate for the TLE using four-dimensional computed tomography (4D-CT).

Materials and methods

We analyzed data from 21 lung tumor patients with fiducial markers; 11 for TLE determination and 10 for validation. Shifted CT images were generated by aligning the centroids of the fiducial markers in the reference phase of 4D-CT with those in each respiratory phase, and the union of gross tumor volumes (GTVs) was determined (G T V u n i o n s h i f t ). Conversely, variations in GTV centroids across the respiratory phases were calculated, and the 95th percentile of the root mean square error was defined as the TLE. Using this TLE, a GTV with an added TLE (G T V T L E r e f ) was generated in the reference phase. Subsequently, a treatment plan assuming dynamic tumor tracking (DTT) was created for the planning target volume, derived by adding an isotropic 5 mm margin toG T V T L E r e f , and the dose coverage forG T V u n i o n s h i f t was evaluated.

Results

The TLEs (standard deviations of the root mean square error) were 2.0 (0.8) mm, 2.1(0.7) mm, and 3.2 (1.1) mm in the left - right, anterior - posterior, and superior - inferior directions, respectively. A dosimetric evaluation revealed thatG T V u n i o n s h i f t did not receive 100 % of the prescribed dose in four of 10 cases owing to artifacts.

Conclusion

The TLE can be compensated by adding an anisotropic margin to the GTV in the reference phase, a critical consideration in DTT.

Endovascular Fiducial Placement in Splenic Metastatic Disease as a Novel Option for Radiotherapy: A Case Report

Splenic metastases are rare but difficult-to-treat entities, especially if they recur after initial surgery or ablation. They are particularly difficult to treat with radiation therapy due to their subdiaphragmatic location and the presence of respiratory excursions. This report describes a case in which an endovascular fiducial placement approach was used to mark the splenic metastasis prior to radiation therapy. We present a 77-year-old male with an extensive history of colorectal metastatic disease. After hemicolectomy, the patient showed metastases - first in the spleen and then in the liver. These were treated with locoregional therapy, including radiofrequency ablation (RFA) for the spleen metastasis and RFA and microwave ablation (MWA) for the liver metastases. Contrast-enhanced computed tomography (CT) imaging, eight years after initial therapy, showed two new liver metastases and a recurrent metastasis in the spleen. Percutaneous ablation of the splenic metastasis was deemed too dangerous because of the subdiaphragmatic location of the spleen and the presence of respiratory motion, and the multidisciplinary tumor board, therefore, opted for radiotherapy. To guide radiotherapy, the interventional radiologist chose to place three microcoil fiducial markers (FMs) around the splenic lesion via an endovascular transradial approach. Radiotherapy was successful, and no recurrence of splenic metastasis has been observed during follow-up. In summary, transradial endovascular FM placement in splenic metastatic disease is technically possible from both an interventional radiological and a radiotherapy standpoint.

Dose calculation accuracy of a new high-performance ring-gantry CBCT imaging system for prostate and lung cancer patients

BACKGROUND AND PURPOSE

The recently introduced high-performance CBCT imaging system called HyperSight offers improved Hounsfield units (HU) accuracy, a larger CBCT field-of-view and improved image quality compared to conventional ring gantry CBCT, possibly enabling treatment planning on CBCT imaging directly. In this study, we evaluated whether the dose calculation accuracy on HyperSight CBCT was sufficient for treatment planning in prostate and lung cancer patients.

MATERIALS AND METHODS

HyperSight CBCT was compared to planning CT (pCT) in terms of HU-to-mass density (MD) calibration curves. For twenty prostate patients and twenty lung patients, differences in DVH parameters, and 3D global gamma between dose distributions calculated on pCT and free breathing HyperSight CBCT were evaluated. For this purpose, HyperSight CBCT acquired at the first fraction was rigidly registered to the pCT, delineations from the CT were propagated and the dose was recalculated on the HyperSight CBCT.

RESULTS

For each insert of the HU-to-MD calibration phantom, the HU values of HyperSight CBCT and pCT agreed within 35 HU. For prostate maximum deviations in PTV Dmean, V95% and V107% were 1.8 %, -1.1 % and < 0.1 % respectively. For lung PTV V95% was generally lower (median -1.1 %) and PTV V107% was generally higher (median 1.1 %) on HyperSight CBCT due to breathing motion artifacts. The average (±SD) 2 %/2mm gamma pass rate was 98.7 %±1.2 % for prostate cancer patients and 96.2 %±2.1 % for lung cancer patients.

CONCLUSION

HyperSight CBCT enabled accurate dose calculation for prostate cancer patients, without implementation of a specific HyperSight CBCT-to-MD curve. For lung cancer patients, breathing motion hampered accurate dose calculations.

Design and manufacturing of a dynamically deformable liver phantom for radiotherapy

Phantoms representing anatomical deformations are necessary to investigate and improve dynamic treatments. In this study, we aimed to produce a deformable liver phantom by simulating respiratory motion. The dynamically DEformable Liver Phantom (DELP) is designed to create a human-specific respiratory model and to produce synchronised, repeatable motion with this model. For the deformation effect of this movement, an artificial liver was created using silicone material and mold. A stepper motor was used to compress the liver in the inferior direction according to an adjustable respiratory motion. Reference markers (fiducial) placed on the DELP helped to verify the movement and calculate the deformation. In dynamic deformation tests, the greatest amount of deformation was found in the edge region of the silicone liver. The average deformation was 3.45 ± 0.93 mm when 5 mm amplitude movement was applied and 5.98 ± 0.01 mm when 10 mm amplitude movement was applied. DELP is a deformable liver phantom with motion reproducibility. Its performance in radiotherapy application was evaluated using dosimetric equipment.

Clinical implementation and patient-specific quality assurance solutions for real-time target tracking and dynamic delivery in Radixact synchrony

BACKGROUND

The installation and testing of the first Radixact with Synchrony system in Colombia marked a significant milestone in Latin America's medical landscape. There was a need to devise a robust quality assurance protocol to comprehensively evaluate both dose delivery and motion tracking accuracy. However, testing experiences under clinical conditions have not been extensively reported. Additionally, there are limited recommended measuring devices for Synchrony evaluation.

PURPOSE

To validate and implement an alternative setup for dynamic-PSQA while testing Synchrony's functionality under clinical scenarios, including real-patient motion traces, and to provide guidance to new centers undergoing clinical implementation of Helical Synchrony.

METHODS

This approach involves using the Iba miniPhantomR with strategically placed fiducial markers for configuring Gafchromic-films and array-based setups. When paired with the CIRS Dynamic Platform, this enables an innovative dynamic setup with trackable features for Synchrony delivery testing. Assessment scenarios, including compensation (M1S1) and no-motion compensation (M1S0), were evaluated using 2D-gamma pass rate analysis with multiple clinical gamma criteria. The Synchrony-Simulation feature was used to assess pre-treatment performance and capture the patient's target motion pattern. Synchrony for common clinical cases with patient's motion-traces was validated.

RESULTS

The results for M1S0 and M1S1 demonstrated consistency with previous studies evaluating Synchrony functionality. Analysis using different gamma criteria unveiled dosimetric differences and impacts across various motion ranges. The application of effective kV-dose subtraction for array-based methods is of upmost importance when evaluating dynamic-PSQA with stringent gamma-criteria. However, no significant kV-dose impact on EBT3-Film was detectable.

CONCLUSION

Two implemented configurations for dynamic-PSQA setups were validated and successfully integrated into our clinic. We addressed both the benefits and limitations of array-based and film-based methods. The functionality and limitations of Synchrony were evaluated using the proposed setups. The potential utility of Synchrony-Simulation, along with the proposed patient-case classification table, can offer valuable support for new users during the clinical implementation of Synchrony treatments.

Development of respiratory motion-resolved hepatobiliary phase cine-magnetic resonance imaging for stereotactic body radiotherapy in liver tumor

Cine-magnetic resonance imaging (MRI) has been used to track respiratory-induced motion of the liver and tumor and assist in the accurate delineation of tumor volume. Recent developments in compressed sensitivity encoding (SENSE; CS) have accelerated temporal resolution while maintaining contrast resolution. This study aimed to develop and assess hepatobiliary phase (HBP) cine-MRI scans using CS. Phantom was imaged using cine-MRI and signal intensity (SI) and contrast ratio (CR) measured to determine the optimal flip-angle turbo field echo (TFE) prepulse delay. We performed cine-MRI in 20 patients for one minute, with images taken every 0.5 s after administration of gadoxetic acid contrast agent. Acquired images had three different acceleration factors (SENSE, CS without denoising [CS-no], and CS with strong denoising [CS-strong]). The image quality of the HBP cine MRI was quantitatively and qualitatively analyzed. In the phantom study, a flip angle of 30 °and TFE prepulse delay of 150 ms were optimal for clinical imaging. In a clinical study, CS-strong showed the highest signal-to-noise ratio and comparable contrast ratio among the three sequences. The CS-strong group showed a significantly higher image quality (P < 0.01), except for motion smoothness (P = 0.11). CS with denoising improved the tumor-to-liver contrast and image quality in high-temporal-resolution HBP cine MRI.

Patient Positional Uncertainty and Margin Reduction in Lung Stereotactic Ablative Radiation Therapy Using Pneumatic Abdominal Compression

PURPOSE

Motion management presents a significant challenge in thoracic stereotactic ablative radiation therapy (SABR). Currently, a 5.0-mm standard planning target volume (PTV) margin is widely used to ensure adequate dose to the tumor. Considering recent advancements in tumor localization and motion management, there is merit to reassessing the necessary PTV margins for modern techniques. This work presents a large-scale analysis of intrafraction repositioning for lung SABR under forced shallow breathing to determine the margin requirements for modern delivery techniques.

METHODS AND MATERIALS

Treatment data for 124 lung SABR patients treated in 607 fractions on a linear accelerator were retrospectively collected for analysis. All patients were treated using pneumatic abdominal compression and intrafraction 4-dimensional (4D) cone beam computed tomography (4D CBCT)-guided repositioning halfway through treatment. Executed repositioning shifts were collected and used to calculate margin requirements using the 2-SD method and an analytical model which accounts for systematic and random errors in treatment.

RESULTS

A total of 85.7% of treated fractions had 3-dimensional repositioning shifts under 5.0 mm. Fifty-three fractions (8.7%) had shifts ≥ 5.0 mm in at least 1 direction. Margins in the right-left, inferior-superior, and posterior-anterior directions were 3.62 mm, 4.34 mm, and 3.50 mm, respectively, calculated using the 2-SD method. The analytical approach estimated that 4.01 mm, 4.37 mm, and 3.95 mm margins were appropriate for our workflow. Executing intrafraction repositioning reduced margin requirements by 0.73 ± 0.07 mm.

CONCLUSIONS

Clinical data suggest that the uniform 5.0-mm margin is conservative for our workflow. Using modern techniques such as 4D CT, 4D CBCT, and effective motion management can significantly reduce required margins, and therefore necessary healthy tissue dose. However, the limitations of margin calculation models must be considered, and margin reduction must be approached with caution. Users should conduct a formal risk assessment prior to adopting new standard PTV margins.

Calibration and volunteer testing of a prototype contactless respiratory motion detection system based on laser tracking

PURPOSE

The goal of this study was to assess the feasibility of a cost-effective prototype of a laser-based respiratory motion detection system utilizing a Leuze LDS for breath monitoring through calibration and volunteer tests.

METHODS

This study was performed using the Anzai AZ-773 V and computerized imaging reference systems (CIRS) motion phantoms for calibration tests. The calibration of the laser-based respiratory motion detection system involved spatial accuracy testing, amplitude calibration, and temporal accuracy. Volunteer testing was conducted on eight volunteers at the inferior end of the sternum and the abdomen area. The accuracy of the data recorded by the laser-based respiratory motion detection system was validated against established clinical reference tracking systems namely real-time position management (RPM) and Anzai AZ-733 V system.

RESULTS

Calibration with an Anzai AZ-773 V and CIRS phantoms demonstrated an average error of 1.17% ± 0.64% and an average amplitude calibration correlation coefficient of 0.975 ± 0.004. Volunteer tests, compared to the Anzai AZ-733 V clinical system and RPM system, revealed average correlation coefficients for deep inspiration breath-hold are 0.931 ± 0.02 and 0.936 ± 0.03, respectively, and for free breathing are 0.85 ± 0.07 and 0.77 ± 0.1, respectively.

CONCLUSIONS

Overall, the data suggest that the in-house laser-based respiratory motion detection system performed well, with an error percentage below 10%. A reasonably good correlation coefficient was obtained, indicating that the readings obtained from the laser system are consistent with those set on the phantom and clinical respiratory motion detection systems. Although promising through the calibration process and volunteer tests, further studies are required to generate trigger data linked directly to computerized tomography and linear accelerator facilities, thereby advancing the clinical viability of this innovative laser-based respiratory motion detection system.

Recent Advances and Current Challenges in Stereotactic Body Radiotherapy for Ultra-Central Lung Tumors

Stereotactic body radiotherapy has been established as a viable treatment option for inoperable early-stage non-small cell lung cancer or secondary lesions mainly in oligoprogressive/oligometastatic scenarios. Treating lesions in the so-called "no flight zone" has always been challenging and conflicting data never cleared how to safely treat these lesions. This is truer considering ultra-central lesions, i.e., directly abutting or whose PTV is overlapping critical mediastinal organs. While historical retrospective data are abundant but mostly heterogenous in terms of the definition of ultra-central lesions, dosing regimens and outcomes, prospective data remain scarce, even though recently published studies have given new encouraging results for such delicate treatment scenarios. For this reason, we aimed to review and summarize current knowledge on stereotactic radiation treatment for ultra-central thoracic lesions, highlighting the most recent advances and the messages that can be taken from them. Lastly, we propose a workflow of the necessary steps to identify and treat such patients, therefore helping in elucidating the advantages and caveats of such treatment options.

Data-Driven Volumetric Computed Tomography Image Generation From Surface Structures Using a Patient-Specific Deep Leaning Model

PURPOSE

Optical surface imaging presents radiation-dose-free and noninvasive approaches for image guided radiation therapy, allowing continuous monitoring during treatment delivery. However, it falls short in cases where correlation of motion between body surface and internal tumor is complex, limiting the use of purely surface guided surrogates for tumor tracking. Relying solely on surface guided radiation therapy (SGRT) may not ensure accurate intrafractional monitoring. This work aims to develop a data-driven framework, mitigating the limitations of SGRT in lung cancer radiation therapy by reconstructing volumetric computed tomography (CT) images from surface images.

METHODS AND MATERIALS

We conducted a retrospective analysis involving 50 patients with lung cancer who underwent radiation therapy and had 10-phase 4-dimensional CT (4DCT) scans during their treatment simulation. For each patient, we used 9 phases of 4DCT images for patient-specific model training and validation, reserving 1 phase for testing purposes. Our approach employed a surface-to-volume image synthesis framework, harnessing cycle-consistency generative adversarial networks to transform surface images into volumetric representations. The framework was extensively validated using an additional 6-patient cohort with resimulated 4DCT.

RESULTS

The proposed technique has produced accurate volumetric CT images from the patient's body surface. In comparison with the ground truth CT images, those generated synthetically by the proposed method exhibited the gross tumor volume center of mass difference of 1.72 ± 0.87 mm, the overall mean absolute error of 36.2 ± 7.0 HU, structural similarity index measure of 0.94 ± 0.02, and Dice score coefficient of 0.81 ± 0.07. Furthermore, the robustness of the proposed framework was found to be linked to respiratory motion.

CONCLUSIONS

The proposed approach provides a novel solution to overcome the limitation of SGRT for lung cancer radiation therapy, which can potentially enable real-time volumetric imaging during radiation treatment delivery for accurate tumor tracking without radiation-induced risk. This data-driven framework offers a comprehensive solution to tackle motion management in radiation therapy, without necessitating the rigid application of first principles modeling for organ motion.

Cardiac substructure delineation in radiation therapy - A state-of-the-art review

Delineation of cardiac substructures is crucial for a better understanding of radiation-related cardiotoxicities and to facilitate accurate and precise cardiac dose calculation for developing and applying risk models. This review examines recent advancements in cardiac substructure delineation in the radiation therapy (RT) context, aiming to provide a comprehensive overview of the current level of knowledge, challenges and future directions in this evolving field. Imaging used for RT planning presents challenges in reliably visualising cardiac anatomy. Although cardiac atlases and contouring guidelines aid in standardisation and reduction of variability, significant uncertainties remain in defining cardiac anatomy. Coupled with the inherent complexity of the heart, this necessitates auto-contouring for consistent large-scale data analysis and improved efficiency in prospective applications. Auto-contouring models, developed primarily for breast and lung cancer RT, have demonstrated performance comparable to manual contouring, marking a significant milestone in the evolution of cardiac delineation practices. Nevertheless, several key concerns require further investigation. There is an unmet need for expanding cardiac auto-contouring models to encompass a broader range of cancer sites. A shift in focus is needed from ensuring accuracy to enhancing the robustness and accessibility of auto-contouring models. Addressing these challenges is paramount for the integration of cardiac substructure delineation and associated risk models into routine clinical practice, thereby improving the safety of RT for future cancer patients.

A feasibility study of tumor motion monitoring for SBRT of lung cancer based on 3D point cloud detection and stacking ensemble learning

PURPOSE

To construct a tumor motion monitoring model for stereotactic body radiation therapy (SBRT) of lung cancer from a feasibility perspective.

METHODS

A total of 32 treatment plans for 22 patients were collected, whose planning CT and the centroid position of the planning target volume (PTV) were used as the reference. Images of different respiratory phases in 4DCT were acquired to redefine the targets and obtain the floating PTV centroid positions. In accordance with the planning CT and CBCT registration parameters, data augmentation was accomplished, yielding 2130 experimental recordings for analysis. We employed a stacking multi-learning ensemble approach to fit the 3D point cloud variations of body surface and the change of target position to construct the tumor motion monitoring model, and the prediction accuracy was assess using root mean squared error (RMSE) and R-Square (R2).

RESULTS

The prediction displacement of the stacking ensemble model shows a high degree of agreement with the reference value in each direction. In the first layer of model, the X direction (RMSE =0.019 ∼ 0.145mm, R2 =0.9793∼0.9996) and the Z direction (RMSE = 0.051 ∼ 0.168 mm, R2 = 0.9736∼0.9976) show the best results, while the Y direction ranked behind (RMSE = 0.088 ∼ 0.224 mm, R2 = 0.9553∼ 0.9933). The second layer model summarizes the advantages of unit models of first layer, and RMSE of 0.015 mm, 0.083 mm, 0.041 mm, and R2 of 0.9998, 0.9931, 0.9984 respectively for X, Y, Z were obtained.

CONCLUSIONS

The tumor motion monitoring method for SBRT of lung cancer has potential application of non-ionization, non-invasive, markerless, and real-time.

A Respiratory Signal Monitoring Method Based on Dual-Pathway Deep Learning Networks in Image-Guided Robotic-Assisted Intervention System

BACKGROUND

Percutaneous puncture procedures, guided by image-guided robotic-assisted intervention (IGRI) systems, are susceptible to disruptions in patients' respiratory rhythm due to factors such as pain and psychological distress.

METHODS

We developed an IGRI system with a coded structured light camera and a binocular camera. Our system incorporates dual-pathway deep learning networks, combining convolutional long short-term memory (ConvLSTM) and point long short-term memory (PointLSTM) modules for real-time respiratory signal monitoring.

RESULTS

Our in-house dataset experiments demonstrate the superior performance of the proposed network in accuracy, precision, recall and F1 compared to separate use of PointLSTM and ConvLSTM for respiratory pattern classification.

CONCLUSION

In our IGRI system, a respiratory signal monitoring module was constructed with a binocular camera and dual-pathway deep learning networks. The integrated respiratory monitoring module provides a basis for the application of respiratory gating technology to IGRI systems and enhances surgical safety by security mechanisms.

A systematic review of the impact of abdominal compression and breath-hold techniques on motion, inter-fraction set-up errors, and intra-fraction errors in patients with hepatobiliary and pancreatic malignancies

BACKGROUND AND PURPOSE

Reducing motion is vital when radiotherapy is used to treat patients with hepatobiliary (HPB) and pancreatic malignancies. Abdominal compression (AC) and breath-hold (BH) techniques aim to minimise respiratory motion, yet their adoption remains limited, and practices vary. This review examines the impact of AC and BH on motion, set-up errors, and patient tolerability in HPB and pancreatic patients.

MATERIALS AND METHODS

This systematic review, conducted using PRISMA and PICOS criteria, includes publications from January 2015 to February 2023. Eligible studies focused on AC and BH interventions in adults with HPB and pancreatic malignancies. Endpoints examined motion, set-up errors, intra-fraction errors, and patient tolerability. Due to study heterogeneity, Synthesis Without Meta-Analysis was used, and a 5 mm threshold assessed the impact of motion mitigation.

RESULTS

In forty studies, 14 explored AC and 26 BH, with 20 on HPB, 13 on pancreatic, and 7 on mixed cohorts. Six studied pre-treatment, 22 inter/intra-fraction errors, and 12 both. Six AC pre-treatment studies showed > 5 mm motion, and 4 BH and 2 AC studies reported > 5 mm inter-fraction errors. Compression studies commonly investigated the arch and belt, and DIBH was the predominant BH technique. No studies compared AC and BH. There was variation in the techniques, and several studies did not follow standardised error reporting. Patient experience and tolerability were under-reported.

CONCLUSION

The results indicate that AC effectively reduces motion, but its effectiveness may vary between patients. BH can immobilise motion; however, it can be inconsistent between fractions. The review underscores the need for larger, standardised studies and emphasizes the importance of considering the patient's perspective for tailored treatments.

FLASH Radiotherapy: Benefits, Mechanisms, and Obstacles to Its Clinical Application

Radiotherapy (RT) has been shown to be a cornerstone of both palliative and curative tumor care. RT has generally been reported to be sharply limited by ionizing radiation (IR)-induced toxicity, thereby constraining the control effect of RT on tumor growth. FLASH-RT is the delivery of ultra-high dose rate (UHDR) several orders of magnitude higher than what is presently used in conventional RT (CONV-RT). The FLASH-RT clinical trials have been designed to examine the UHDR deliverability, the effectiveness of tumor control, the dose tolerance of normal tissue, and the reproducibility of treatment effects across several institutions. Although it is still in its infancy, FLASH-RT has been shown to have potential to rival current RT in terms of safety. Several studies have suggested that the adoption of FLASH-RT is very limited, and the incorporation of this new technique into routine clinical RT will require the use of accurate dosimetry methods and reproducible equipment that enable the reliable and robust measurements of doses and dose rates. The purpose of this review is to highlight the advantages of this technology, the potential mechanisms underpinning the FLASH-RT effect, and the major challenges that need to be tackled in the clinical transfer of FLASH-RT.

[A Comparison of Tumor Respiratory Motion Evaluation Methods Using Dynamic Thorax Motion Phantom]

PURPOSE

We evaluated the measurement accuracy and time efficiency of the tumor respiratory motion evaluation methods using a dynamic thorax motion phantom.

METHODS

A total of 12 patterns of 4DCT images with different tumor displacements and artifacts were used for the measurement. Three methods were employed to measure tumor motion. The first method was the manual delineation of the tumor on each phase CT image with a treatment planning system (RTPS [Manual]). The second method was the automatic delineation of the tumor structure by deformation and copying (RTPS [Auto]). The third method was tumor motion analysis software (Simple 4D Analysis Ver.1.3.1 [Simple 4D]; Triangle Products, Chiba, Japan). For each method, the difference between the phantom motion and the measured value was determined.

RESULTS

The differences (mean±standard deviation: SD) in the superior-inferior direction for RTPS (Manual), RTPS (Auto), and Simple 4D in the without-artifact images were -0.6 mm±0.6 mm, -5.0 mm±2.2 mm, and -1.0 mm±0.0 mm, respectively. The difference in the left-right and anterior-posterior directions was within 1 mm for all methods. Furthermore, the time required for Simple 4D was shorter than for the other methods.

CONCLUSION

Simple 4D showed the comparable measurement accuracy and improvement time efficiency to RTPS (Manual) and RTPS (Auto), and was useful for tumor respiratory motion analysis.

Imaging error reduction in radial cine-MRI with deep learning-based intra-frame motion compensation

Objective.Radial cine-MRI allows for sliding window reconstruction at nearly arbitrary frame rate, promising high-speed imaging for intra-fractional motion monitoring in magnetic resonance guided radiotherapy. However, motion within the reconstruction window may determine the location of the reconstructed target to deviate from the true real-time position (target positioning errors), particularly in cases of fast breathing or for anatomical structures affected by the heartbeat. In this work, we present a proof-of-concept study aiming to enhance radial cine-MR imaging by implementing deep-learning-based intra-frame motion compensation techniques.Approach.A novel network (TransSin-UNet) was proposed to continuously estimate the final-position image of the target, corresponding to end of the frame acquisition. Within the radial k-space reconstruction window, the spatial-temporal dependencies among the sinogram representation of the spokes were modeled by a transformer encoder subnetwork, followed by a UNet subnetwork operating in the spatial domain for pixel-level fine-tuning. By simulating motion-dependent radial sampling with (tiny) golden angles, we generated datasets from 25 4D digital anthropomorphic lung cancer phantoms. The network was then trained and extensively evaluated across datasets characterized by varying azimuthal radial profile increments.Main Results.The method required additional 4.8 ms per frame over the conventional approach involving direct image reconstruction with motion-corrupted spokes. TransSin-UNet outperformed architectures relying solely on transformer encoders or UNets across all the comparative evaluations, leading to a noticeable enhancement in image quality and target positioning accuracy. The normalized root mean-squared error decreased by 50% from the initial value of 0.188 on average, whereas the mean Dice similarity coefficient of the gross tumor volume increased from 85.1% to 96.2% in the investigated cases. Furthermore, the final-positions of anatomical structures undergoing substantial intra-frame deformations were precisely derived.Significance.The proposed approach enables an effective intra-frame motion compensation, offering an opportunity to reduce errors in radial cine-MR imaging for real-time motion management.

Daily Diagnostic Quality Computed Tomography-on-Rails (CTOR) Image Guidance for Abdominal Stereotactic Body Radiation Therapy (SBRT)

BACKGROUND/OBJECTIVES

Stereotactic body radiation therapy (SBRT) for abdominal targets faces a variety of challenges, including motion caused by the respiration and digestion and a relatively poor level of contrast between the tumor and the surrounding tissues. Breath-hold treatments with computed tomography-on-rails (CTOR) image guidance is one way of addressing these challenges, allowing for both the tumor and normal tissues to be well-visualized. Using isodose lines (IDLs) from CT simulations as a guide, the anatomical information can be used to shift the alignment or trigger a replan, such that normal tissues receive acceptable doses of radiation.

METHODS

This study aims to describe the workflow involved when using CTOR for pancreas and liver SBRT and demonstrates its effectiveness through several case studies.

RESULTS

In these case studies, using the anatomical information gained through diagnostic-quality CT guidance to make slight adjustments to the alignment, resulted in reductions in the maximum dose to the stomach.

CONCLUSIONS

High-quality imaging, such as CTOR, and the use of IDLs to estimate the doses to OARs, enable the safe delivery of SBRT, without the added complexity and resource commitment required by daily online adaptive planning.

Radiotherapy and theranostics: a Lancet Oncology Commission

Following on from the 2015 Lancet Oncology Commission on expanding global access to radiotherapy, Radiotherapy and theranostics: a Lancet Oncology Commission was created to assess the access and availability of radiotherapy to date and to address the important issue of access to the promising field of theranostics at a global level. A marked disparity in the availability of radiotherapy machines between high-income countries and low-income and middle-income countries (LMICs) has been identified previously and remains a major problem. The availability of a suitably trained and credentialled workforce has also been highlighted as a major limiting factor to effective implementation of radiotherapy, particularly in LMICs. We investigated initiatives that could mitigate these issues in radiotherapy, such as extended treatment hours, hypofractionation protocols, and new technologies. The broad implementation of hypofractionation techniques compared with conventional radiotherapy in prostate cancer and breast cancer was projected to provide radiotherapy for an additional 2·2 million patients (0·8 million patients with prostate cancer and 1·4 million patients with breast cancer) with existing resources, highlighting the importance of implementing new technologies in LMICs. A global survey undertaken for this Commission revealed that use of radiopharmaceutical therapy-other than 131I-was highly variable in high-income countries and LMICs, with supply chains, workforces, and regulatory issues affecting access and availability. The capacity for radioisotope production was highlighted as a key issue, and training and credentialling of health professionals involved in theranostics is required to ensure equitable access and availability for patient treatment. New initiatives-such as the International Atomic Energy Agency's Rays of Hope programme-and interest by international development banks in investing in radiotherapy should be supported by health-care systems and governments, and extended to accelerate the momentum generated by recognising global disparities in access to radiotherapy. In this Commission, we propose actions and investments that could enhance access to radiotherapy and theranostics worldwide, particularly in LMICs, to realise health and economic benefits and reduce the burden of cancer by accessing these treatments.

Robust localization of poorly visible tumor in fiducial free stereotactic body radiation therapy

BACKGROUND AND PURPOSE

Effective respiratory motion management reduces healthy tissue toxicity and ensures sufficient dose delivery to lung cancer cells in pulmonary stereotactic body radiation therapy (SBRT) with high fractional doses. An articulated robotic arm paired with an X-ray imaging system is designed for real-time motion-tracking (RTMT) dose delivery. However, small tumors (<15 mm) or tumors at challenging locations may not be visible in the X-ray images, disqualifying patients with such tumors from RTMT dose delivery unless fiducials are implanted via an invasive procedure. To track these practically invisible lung tumors in SBRT, we hereby develop a deep learning-enabled template-free tracking framework, SAFE Track.

METHODS

SAFE Track is a fully supervised framework that trains a generalizable prior for template-free target localization. Two sub-stages are incorporated in SAFE Track, including the initial pretraining on two large-scale medical image datasets (DeepLesion and Node21) followed by fine-tuning on our in-house dataset. A two-stage detector, Faster R-CNN, with a backbone of ResNet50, was selected as our detection network. 94 patients (415 fractions; 40,348 total frames) with low tumor visibility who thus had implanted fiducials were included. The cohort is categorized by the longest dimension of the tumor (<10 mm, 10-15 mm and > 15 mm). The patients were split into training (n = 66) and testing (n = 28) sets. We simulated fiducial-free tumors by removing the fiducials from the X-ray images. We classified the patients into two groups - fiducial implanted inside tumors and implanted outside tumors. To ensure the rigor of our experiment design, we only conducted fiducial removal simulation in training patients and utilized patients with fiducial implanted outside of the tumors for testing. Commercial Xsight Lung Tracking (XLT) and a Deep Match were included for comparison.

RESULTS

SAFE Track achieves promising outcomes to as accurate as 1.23±1.32 mm 3D distance in testing patients with tumor size > 15 mm where Deep Match is at 4.75±1.67 mm and XLT is at 12.23±4.58 mm 3D distance. Even for the most challenging tumor size (<10 mm), SAFE Track maintains its robustness at 1.82 plus or minus 1.67 mm 3D distance, where Deep Match is at 5.32 plus or minus 2.32 mm, and XLT is at 24.83±12.95 mm 3D distance. Moreover, SAFE Track can detect some considerably challenging cases where the tumor is almost invisible or overlapped with dense anatomies.

CONCLUSION

SAFE Track is a robust, clinically compatible, fiducial-free, and template-free tracking framework that is applicable to patients with small tumors or tumors obscured by overlapped anatomies in SBRT.

The Use of Magnetic Resonance Imaging in Radiation Therapy Treatment Simulation and Planning

Ever since its introduction as a diagnostic imaging tool the potential of magnetic resonance imaging (MRI) in radiation therapy (RT) treatment simulation and planning has been recognized. Recent technical advances have addressed many of the impediments to use of this technology and as a result have resulted in rapid and growing adoption of MRI in RT. The purpose of this article is to provide a broad review of the multiple uses of MR in the RT treatment simulation and planning process, identify several of the most used clinical scenarios in which MR is integral to the simulation and planning process, highlight existing limitations and provide multiple unmet needs thereby highlighting opportunities for the diagnostic MR imaging community to contribute and collaborate with our oncology colleagues. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 5.

The Development of Volumetric Quantitative Evaluation Software for Assessing Respiratory-Induced Target Motion

Purpose We developed a volumetric quantitative evaluation software called vector volume histogram (VVH) to evaluate respiratory-induced organ motion using deformable image registration (DIR). Methods The B-spline-based DIR algorithm was used to compute the deformation vector field (DVF), which included the DVFLR (left-right), DVFAP (anterior-posterior), and DVFCC (craniocaudal). The VVH software was written as a plug-in using Python, thus allowing anyone to easily modify the code. A shifted target within the moving phantom was used to evaluate the performance of the VVH software. The 2 cm diameter target was systematically shifted by 5, 10, 15, and 20 mm in the CC direction. To evaluate respiration-induced target motion, the VVH method was applied during the inhalation and exhalation phases of 4D CT scans in a patient with lung cancer. Length at 5% volume (L5%) and length at 50% volume (L50%​​​​​) were calculated to evaluate the target motion. Results In the phantom study, the VVH software accurately measured target displacements with L5% and L50% values of 5.4 mm and 4.8 mm, 10.4 mm and 9.8 mm, 14.9 mm, and 14.6 mm, and 19.9 mm and 19.6 mm for 5, 10, 15 and 20 mm displacements, respectively. For the lung cancer patient study, the VVH method showed target motion with L5% and L50% values of 1.9 mm and 1.8 mm in LR, 1.9 mm and 0.9 mm in AP, 18.8 mm and 15.8 mm in CC, and 18.9 mm and 15.8 mm in 3D vector. The centroid method measured respiratory tumor motion between the inhalation and exhalation phases as 0.5 mm, 0.7 mm, 13.5 mm, and 13.5 mm in the LR, AP, and CC directions and in the 3D vector. Conclusions The VVH software provided a volumetric quantitative assessment of respiratory-induced target motion and may provide strategic decisions for clinical use at the time of treatment planning.

Technical and Quality Considerations for Stereotactic Radiation Treatment Techniques

ABSTRACT

Stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT), collectively termed SRS-SBRT, are advanced treatment modalities delivering high doses of radiation in a single treatment or condensed treatment phase. Due to the small margins and steep dose gradient used in SRS-SBRT, the technical and safety considerations are more stringent than traditional radiation therapy and may include more advanced simulation, patient immobilization, treatment planning, and treatment delivery techniques. Respiratory motion management and intrafraction motion monitoring are often used during SRS-SBRT to ensure treatments are robust to both internal organ motion and patient movement during treatment. To ensure optimal treatment quality, SRS-SBRT programs should use multidisciplinary coordination of care to ensure patient-specific treatment strategies are used for optimal patient outcomes. Quality and safety considerations are presented, including peer review and external validation, for optimizing quality and adhering to national guidelines for stereotactic techniques.

Cardiorespiratory motion characteristics and their dosimetric impact on cardiac stereotactic body radiotherapy

BACKGROUND

Cardiac stereotactic body radiotherapy (CSBRT) is an emerging and promising noninvasive technique for treating refractory arrhythmias utilizing highly precise, single or limited-fraction high-dose irradiations. This method promises to revolutionize the treatment of cardiac conditions by delivering targeted therapy with minimal exposure to surrounding healthy tissues. However, the dynamic nature of cardiorespiratory motion poses significant challenges to the precise delivery of dose in CSBRT, introducing potential variabilities that can impact treatment efficacy. The complexities of the influence of cardiorespiratory motion on dose distribution are compounded by interplay and blurring effects, introducing additional layers of dose uncertainty. These effects, critical to the understanding and improvement of the accuracy of CSBRT, remain unexplored, presenting a gap in current clinical literature.

PURPOSE

To investigate the cardiorespiratory motion characteristics in arrhythmia patients and the dosimetric impact of interplay and blurring effects induced by cardiorespiratory motion on CSBRT plan quality.

METHODS

The position and volume variations in the substrate target and cardiac substructures were evaluated in 12 arrhythmia patients using displacement maximum (DMX) and volume metrics. Moreover, a four-dimensional (4D) dose reconstruction approach was employed to examine the dose uncertainty of the cardiorespiratory motion.

RESULTS

Cardiac pulsation induced lower DMX than respiratory motion but increased the coefficient of variation and relative range in cardiac substructure volumes. The mean DMX of the substrate target was 0.52 cm (range: 0.26-0.80 cm) for cardiac pulsation and 0.82 cm (range: 0.32-2.05 cm) for respiratory motion. The mean DMX of the cardiac structure ranged from 0.15 to 1.56 cm during cardiac pulsation and from 0.35 to 1.89 cm during respiratory motion. Cardiac pulsation resulted in an average deviation of -0.73% (range: -4.01%-4.47%) in V25 between the 3D and 4D doses. The mean deviations in the homogeneity index (HI) and gradient index (GI) were 1.70% (range: -3.10%-4.36%) and 0.03 (range: -0.14-0.11), respectively. For cardiac substructures, the deviations in D50 due to cardiac pulsation ranged from -1.88% to 1.44%, whereas the deviations in Dmax ranged from -2.96% to 0.88% of the prescription dose. By contrast, the respiratory motion led to a mean deviation of -1.50% (range: -10.73%-4.23%) in V25. The mean deviations in HI and GI due to respiratory motion were 4.43% (range: -3.89%-13.98%) and 0.18 (range: -0.01-0.47) (p < 0.05), respectively. Furthermore, the deviations in D50 and Dmax in cardiac substructures for the respiratory motion ranged from -0.28% to 4.24% and -4.12% to 1.16%, respectively.

CONCLUSIONS

Cardiorespiratory motion characteristics vary among patients, with the respiratory motion being more significant. The intricate cardiorespiratory motion characteristics and CSBRT plan complexity can induce substantial dose uncertainty. Therefore, assessing individual motion characteristics and 4D dose reconstruction techniques is critical for implementing CSBRT without compromising efficacy and safety.

Robust Real-Time Cancer Tracking via Dual-Panel X-Ray Images for Precision Radiotherapy

Respiratory-induced tumor motion presents a critical challenge in lung cancer radiotherapy, potentially impacting treatment precision and efficacy. This study introduces an innovative, deep learning-based approach for real-time, markerless lung tumor tracking utilizing orthogonal X-ray projection images. It incorporates three key components: (1) a sophisticated data augmentation technique combining a hybrid deformable model with 3D thin-plate spline transformation, (2) a state-of-the-art Transformer-based segmentation network for precise tumor boundary delineation, and (3) a CNN regression network for accurate 3D tumor position estimation. We rigorously evaluated this approach using both patient data from The Cancer Imaging Archive and dynamic thorax phantom data, assessing performance across various noise levels and comparing it with current leading algorithms. For TCIA patient data, the average DSC and HD95 values were 0.9789 and 1.8423 mm, respectively, with an average centroid localization deviation of 0.5441 mm. On CIRS phantoms, DSCs were 0.9671 (large tumor) and 0.9438 (small tumor) with corresponding HD95 values of 1.8178 mm and 1.9679 mm. The 3D centroid localization accuracy was consistently below 0.33 mm. The processing time averaged 90 ms/frame. Even under high noise conditions (S2 = 25), errors for all data remained within 1 mm with tracking success rates mostly at 100%. In conclusion, the proposed markerless tracking method demonstrates superior accuracy, noise robustness, and real-time performance for lung tumor localization during radiotherapy. Its potential to enhance treatment precision, especially for small tumors, represents a significant step toward improving radiotherapy efficacy and personalizing cancer treatment.