Magnetic Resonance Imaging-Guided vs Computed Tomography-Guided Stereotactic Body Radiotherapy for Prostate Cancer: The MIRAGE Randomized Clinical Trial

Preclinical monitoring of radiation-induced brain injury via GluCEST MRI and resting-state fMRI at 7 T: an exploratory study on MRI-guided OAR avoidance

PURPOSE

To assess the value of glutamate chemical exchange saturation transfer (GluCEST) after whole-brain radiotherapy (WBRT) as an imaging marker of radiation-induced brain injury (RBI) and to preliminarily show the feasibility of multiparametric MRI-guided organ at risk (OAR) avoidance.

METHODS

Rats were divided into two groups: the control (CTRL) group (n = 9) and the RBI group (n = 9). The rats in the RBI group were irradiated with an X‑ray radiator and then subjected to a water maze experiment 4 weeks later. In combination with high-performance liquid chromatography (HPLC), we evaluated the value of GluCEST applied to glutamate changes for RBI and investigated the effect of such changes on glutamatergic neuronal function.

RESULTS

The average GluCEST values were markedly lower in the hippocampus and cerebral cortex. Positive correlations were observed between GluCEST values and regional homogeneity (ReHo) values in both the hippocampus and the cerebral cortex. HPLC showed a positive correlation with GluCEST values in the hippocampus. GluCEST values were positively correlated with spatial memory.

CONCLUSION

GluCEST MRI provides a visual assessment of glutamate changes in RBI rats for monitoring OAR cognitive toxicity reactions and may be used as a biomarker of OAR avoidance as well as metabolism to facilitate monitoring and intervention in radiation damage that occurs after radiotherapy.

Artificial Intelligence, Machine Learning and Big Data in Radiation Oncology

This review explores the applications of artificial intelligence and machine learning (AI/ML) in radiation oncology, focusing on computer vision (CV) and natural language processing (NLP) techniques. We examined CV-based AI/ML in digital pathology and radiomics, highlighting the prospective clinical studies demonstrating their utility. We also reviewed NLP-based AI/ML applications in clinical documentation analysis, knowledge assessment, and quality assurance. While acknowledging the challenges for clinical adoption, this review underscores the transformative potential of AI/ML in enhancing precision, efficiency, and quality of care in radiation oncology.

Multidisciplinary consensus prostate contours on magnetic resonance imaging: educational atlas and reference standard for artificial intelligence benchmarking

INTRODUCTION

Evaluation of artificial intelligence (AI) algorithms for prostate segmentation is challenging because ground truth is lacking. We aimed to (1) create a reference standard dataset with precise prostate contours by expert consensus and (2) evaluate various AI tools against this standard.

MATERIALS AND METHODS

We obtained prostate MRI cases from XXX. A panel of four experts (two genitourinary radiologists, two prostate radiation oncologists) meticulously developed consensus prostate segmentations on axial T2-weighted series. We evaluated the performance of six AI tools (three commercially available, three academic) using Dice scores, distance from reference contour, and volume error.

RESULTS

The panel achieved consensus prostate segmentation on each slice of all 68 patient cases included in the reference dataset. We present two patient examples to serve as contouring guides. Depending on the AI tool, median Dice scores (across patients) ranged from 0.80 to 0.94 for whole prostate segmentation. For a typical (median) patient, AI tools had a mean error over the prostate surface ranging from 1.3 to 2.4 mm. They maximally deviated 3.0 to 9.4 mm outside the prostate and 3.0 to 8.5 mm inside the prostate for a typical patient. Error in prostate volume measurement for a typical patient ranged from 4.3% to 31.4%.

DISCUSSION

We established an expert consensus benchmark for prostate segmentation. The best-performing AI tools have typical accuracy greater than that reported for radiation oncologists using CT scans (most common clinical approach for radiotherapy planning). Physician review remains essential to detect occasional major errors.

Stereotactic Magnetic Resonance Guided Adaptive Radiation Therapy for Infradiaphragmatic Oligometastatic Disease: Disrupting the One-Size-Fits-All Paradigm

PURPOSE

Although recent studies have demonstrated the benefits of stereotactic ablative radiotherapy (SABR) in the treatment of oligometastatic (OM) disease, toxicity remains a concern in the infradiaphragmatic region. This is largely because of challenges in soft tissue visualization, motion management, and the proximity of gastrointestinal organs at risk. Stereotactic magnetic resonance guided adaptive radiation therapy (SMART) may enhance the safety and efficacy of SABR in abdominopelvic targets.

METHODS AND MATERIALS

Patients with infradiaphragmatic OM disease, including up to 5 lesions treated with SMART between May 2018 and September 2023, were evaluated. Progression-free survival, overall survival, and local control (LC) were analyzed using Kaplan-Meier and Fine and Gray proportional subhazards models, whereas treatment-related toxicities were assessed using the National Cancer Institute Common Terminology Criteria for Adverse Events v4.0 criteria.

RESULTS

One hundred eighty-three targets in 138 patients with primarily lung, colorectal, and noncolorectal gastrointestinal cancers were prescribed a median dose of 50 Gy in 5 fractions on a 0.35-T magnetic resonance-Linac. Overall, 62.8% of treated metastases were within 5 mm of a dose-limiting organs at risk, necessitating online adaptive planning in 670 of 875 (76.6%) delivered SABR fractions. The 1-year progression-free survival rate was 35.8% for the entire population and significantly differed between OM and oligoprogressive patients (42.4% vs 25.4%, P = .03). There was a trend toward lower LC in colorectal versus noncolorectal histology in the definitive dose group (biologically effective dose10 ≥ 75 Gy) with 2-year LC rates of 74.0% versus 86.0%, respectively, P = .08. Acute and late grade ≥3 toxicities were 0% and 2.2%, respectively.

CONCLUSIONS

SMART is feasible and effective for treating OM disease lesions in proximity to dose-limited organs at risk. Safe dose escalation is facilitated by online adaptive radiation therapy and is associated with long-term LC. Patient selection is key to identifying which patients with OM or oligoprogressive disease should be considered most appropriate for SMART.

Hypofractionated radiotherapy for prostate cancer (HYDRA): an individual patient data meta-analysis of randomised trials in the MARCAP consortium

BACKGROUND

Trials comparing moderately hypofractionated radiotherapy (MHFRT) to conventionally-fractionated radiotherapy (CFRT) for prostate cancer have varied considerably in intent (non-inferiority vs superiority) and MHFRT dose. We compare the efficacy and toxicity profiles of isodose MHFRT and dose-escalated MHFRT.

METHODS

This was an individual patient data meta-analysis that identified randomised phase 3 trials of CFRT versus MHFRT that had published individual patient-level data on efficacy and late toxicity. A systematic literature search using MEDLINE, Embase, trial registries, the Web of Science, Scopus, and relevant conference proceedings was initially conducted on Dec 15, 2023, and was re-conducted on Jan 8, 2025. Trials that did not publish efficacy data, did not publish late toxicity data, or did not use modern dose radiotherapy (≥70 Gy in 2 Gy equivalents) in the CFRT group were excluded. Individual patient data were provided to MARCAP by study investigators. Three separate meta-analyses were designed to compare efficacy (primary endpoint was progression-free survival), physician-scored late toxicity (co-primary endpoints were late grade 2 or higher genitourinary and late grade 2 or higher gastrointestinal toxic effects), and patient-reported outcomes (co-primary endpoints were clinically-significant decrements in patient-reported urinary or bowel quality of life) between patients receiving CFRT versus MHFRT.

FINDINGS

We identified 1696 records for review. Seven phase 3 trials comparing MHFRT with CFRT were eligible for inclusion in our analysis. Individual patient data were obtained from these seven studies (3454 patients from three trials comparing CFRT with isodose MHFRT and 2426 patients from four trials comparing CFRT with dose-escalated MHFRT). At a median follow-up of 5·4 years (IQR 4·6-7·2) for isodose MHFRT and 7·1 years (5·7-8·4) for dose-escalated MHFRT, no differences in progression-free survival were detected (hazard ratio 0·92, 95% CI 0·81-1·05; p=0·21 and 0·94, 0·82-1·09; p=0·43 respectively). No increased odds of grade 2 or higher genitourinary toxic effects were identified for either isodose (odds ratio [OR] 1·16, 95 CI% 0·86-1·57; p=0·32) or dose-escalated MHFRT (1·20, 0·95-1·51; p=0·13). The odds of grade 2 or higher gastrointestinal toxic effects were significantly higher with dose-escalated (OR 1·48, 95% CI 1·14-1·92; p=0·0035) but not isodose MHFRT (1·30, 0·59-2·87; p=0·51). Isodose MHFRT was not found to show different odds of urinary quality-of-life decrement (OR 1·03, 95% CI 0·51-2·09; p=0·93) or bowel quality-of-life decrement (0·76, 0·40-1·43; p=0·39). Dose-escalated MHFRT was associated with greater odds of bowel quality-of-life decrement (OR 1·68, 95% CI 1·07-2·61; p=0·023), but no evidence of greater urinary quality-of-life decrement was found (1·57, 0·87-2·85; p=0·13).

INTERPRETATION

Isodose MHFRT and dose-escalated MHFRT both have similar efficacy compared with CFRT, but dose-escalated MHFRT is associated with higher physician-scored and patient-reported bowel toxicity. Isodose regimens, eg, 60 Gy in 20 fractions, should be the standard MHFRT regimen for localised prostate cancer.

FUNDING

None.

Facilitating 1.5T MR-Linac adoption: Workflow strategies and practical tips

BACKGROUND

MR-guided radiotherapy (MRgRT) offers new opportunities but also introduces workflow complexities requiring dedicated optimization. Implementing magnetic resonance linear accelerator (MR-Linac) technology comes with challenges such as prolonged treatment times and workflow integration issues.

PURPOSE

We present here our experience and share practical tips and tricks to streamline MR-Linac implementation, optimize workflow efficiency, and improve coordination.

METHODS

The first 150 patients treated with a 1.5T MR-Linac Unity® at our institution were analyzed. Treatments were assessed based on session recordings, difficulties encountered were identified, and solutions documented.

RESULTS

A total of 726 fractions were delivered, with a mean treatment time of 48 minutes. Key optimizations included standardized operating procedures (SOPs) and structured briefing sheets, leading to reduced delays and improved treatment consistency.

CONCLUSION

Strategic workflow standardization and optimized communication tools significantly improved the ability to deliver high-quality, patient-centered care by streamlining processes and enhancing coordination among team members. These insights provide practical guidance for centers integrating MR-Linac technology.

Acute toxicity and quality of life after margin reduction using a sub-fractionation workflow for stereotactic radiotherapy of localized prostate cancer on a 1.5 Tesla MR-linac

BACKGROUND AND PURPOSE

A sub-fractionation workflow to correct for intrafraction motion in localized prostate cancer radiotherapy was implemented at our center, allowing for PTV margin reduction from isotropic 5 mm to 2 mm in cranio-caudal and left-right directions and 3 mm in the anterior-posterior direction. The purpose of this study was to assess differences in acute toxicity before and after margin reduction.

MATERIALS AND METHODS

Included patients were treated with 36.25 Gy in five fractions on a 1.5 T MR-linac, with PTV margins of 5 mm (standard margins) or 2-3 mm (tight margins). The primary endpoint was acute (90 days post-RT) toxicity. Physician-reported toxicity was measured by maximum CTCAE version 5.0 genitourinary (GU) and gastrointestinal (GI) scores. Patient reported toxicity was a secondary endpoint, assessed through EPIC-26 urinary and bowel domain scores. Groups were balanced through propensity score matching after multiple imputation using chained equations. Pearson's Chi-squared tests were used to analyze CTCAE scores and Wilcoxon rank sum tests to analyze EPIC-26 scores.

RESULTS

299 eligible patients were identified (193 and 106 in the tight and standard margin groups, respectively). After matching, 212 patients (106 per treatment group) were available for assessment. No statistically significant between-group differences in physician-reported toxicity were observed at any follow-up point. Patient-reported urinary irritative/obstructive quality of life was statistically, but not clinically, significantly higher after one month. Overall, scores declined during treatment and one month post-RT, but returned to baseline levels three months post-RT.

CONCLUSION

Margin reduction below 5 mm did not seem to reduce acute toxicity after radiotherapy with a stereotactic body radiotherapy (SBRT) treatment schedule in localized prostate cancer. The introduction of real-time comprehensive motion management with prostate gating could further lower GU and GI toxicity and ameliorate treatment related quality of life.

Training for tomorrow: Establishing a worldwide curriculum in online adaptive radiation therapy

This commentary discusses the implementation of online adaptive radiation therapy (oART) in cancer treatment within the context of current challenges faced by radiation therapy professionals. oART enables modifications to treatment plans based on daily imaging, enhancing target accuracy while minimising harm to surrounding organs. Despite its potential to improve patient outcomes, the application of oART is hindered by notable barriers, particularly in human resources. A global shortage of skilled radiation professionals such as radiation therapists or therapeutic radiographers (RTTs), medical physicists and radiation oncologists, along with training challenges in online adaptive techniques, hinders oART implementation and sustainability. Moreover, geographical disparities limit access to advanced training programs, leaving RTTs and their patients in underserved regions at a disadvantage. There is growing global evidence that RTTs are being successfully trained to lead adaptive fractions in both cone-beam computed tomography and magnetic resonance imaging guided oART. This commentary proposes the notion of standards for a global training curriculum to address barriers and expand RTT capabilities in delivering oART. By leveraging artificial intelligence and fostering interdisciplinary collaboration, the radiation therapy field can enhance efficiency and accuracy in oART. Successful training models from leading institutions illustrate the importance of hands-on experience and ongoing mentorship. A coordinated effort among stakeholders is essential to establish a comprehensive global training framework, ultimately improving patient access to oART and elevating standards of care worldwide.

Predictive Model of Acute Rectal Toxicity in Prostate Cancer Treated With Radiotherapy

PURPOSE

To aid personalized treatment selection, we developed a predictive model for acute rectal toxicity in patients with prostate cancer undergoing radiotherapy with photons and protons.

MATERIALS AND METHODS

We analyzed a prospective multi-institutional cohort of 278 patients treated from 2012 to 2023 across 10 centers. Dosimetric and nondosimetric variables were collected, and key predictors were identified using purposeful feature selection. The cohort was split into discovery (n = 227) and validation (n = 51) data sets. The dose along the rectum surface was transformed into a two-dimensional surface, and dose-area histograms (DAHs) were quantified. A convolutional neural network (CNN) was developed to extract dosimetric features from the DAH and integrate them with nondosimetric predictors. Model performance was benchmarked against logistic regression (LR) using the AUC.

RESULTS

Key predictors included rectum length, race, age, and hydrogel spacer use. The CNN model demonstrated stability in the discovery data set (AUC = 0.81 ± 0.11) and outperformed LR in the validation data set (AUC = 0.81 v 0.54). Separate analysis of photon and proton subsets yielded consistent AUCs of 0.7 and 0.92, respectively. In the photon high-risk group, the model achieved 83% sensitivity, and in proton subsets, it achieved 100% sensitivity and specificity, indicating the potential to be used for treatment selection in these patients.

CONCLUSION

Our novel approach effectively predicts rectal toxicity across photon and proton subsets, demonstrating the utility of integrating dosimetric and nondosimetric features. The model's strong performance across modalities suggests potential for guiding treatment decisions, warranting prospective validation.

MR-linac: role of artificial intelligence and automation

The integration of artificial intelligence (AI) into radiotherapy has advanced significantly during the past 5 years, especially in terms of automating key processes like organ at risk delineation and treatment planning. These innovations have enhanced consistency, accuracy, and efficiency in clinical practice. Magnetic resonance (MR)-guided linear accelerators (MR-linacs) have greatly improved treatment accuracy and real-time plan adaptation, particularly for tumors near radiosensitive organs. Despite these improvements, MR-guided radiotherapy (MRgRT) remains labor intensive and time consuming, highlighting the need for AI to streamline workflows and support rapid decision-making. Synthetic CTs from MR images and automated contouring and treatment planning will reduce manual processes, thus optimizing treatment times and expanding access to MR-linac technology. AI-driven quality assurance will ensure patient safety by predicting machine errors and validating treatment delivery. Advances in intrafractional motion management will increase the accuracy of treatment, and the integration of imaging biomarkers for outcome prediction and early toxicity assessment will enable more precise and effective treatment strategies.

The TROG 15.01 stereotactic prostate adaptive radiotherapy utilizing kilovoltage intrafraction monitoring (SPARK) clinical trial database

PURPOSE

The US National Institutes of Health state that Sharing of clinical trial data has great potential to accelerate scientific progress and ultimately improve public health by generating better evidence on the safety and effectiveness of therapies for patients (https://www.ncbi.nlm.nih.gov/books/NBK285999/ accessed 2024-01-24.). Aligned with this initiative, the Trial Management Committee of the Trans-Tasman Radiation Oncology Group (TROG) 15.01 Stereotactic Prostate Adaptive Radiotherapy utilizing Kilovoltage intrafraction monitoring (KIM) (SPARK) clinical trial supported the public sharing of the clinical trial data.

ACQUISITION AND VALIDATION METHODS

The data originate from the TROG 15.01 SPARK clinical trial. The SPARK trial was a phase II prospective multi-institutional clinical trial (NCT02397317). The aim of the SPARK clinical trial was to measure the geometric and dosimetric cancer targeting accuracy achieved with a real-time image-guided radiotherapy technology named KIM for 48 prostate cancer patients treated in 5 treatment sessions. During treatment, real-time tumor translational and rotational motion were determined from x-ray images using the KIM technology. A dose reconstruction method was used to evaluate the dose delivered to the target and organs-at-risk. Patient-reported outcomes and toxicity data were monitored up to 2 years after the completion of the treatment.

DATA FORMAT AND USAGE NOTES

The dataset contains planning CT images, treatment plans, structure sets, planned and motion-included dose-volume histograms, intrafraction kilovoltage, and megavoltage projection images, tumor translational and rotational motion determined by KIM, tumor motion ground truth data, the linear accelerator trajectory traces, and patient treatment outcomes. The dataset is publicly hosted by the University of Sydney eScholarship Repository at https://doi.org/10.25910/qg5d-6058.

POTENTIAL APPLICATIONS

The 3.6 Tb dataset, with approximately 1 million patient images, could be used for a variety of applications, including the development of real-time image-guided methods, adaptation strategies, tumor, and normal tissue control modeling, and prostate-specific antigen kinetics.

« Augmented radiotherapy » in the management of high-risk prostate cancer (PCa): A systematic review

BACKGROUND

In patients with high-risk (HR) prostate cancer (PCa) treated with radiotherapy and androgen deprivation therapy (ADT), intensification with androgen receptor pathway inhibitor (ARPI) improves overall survival (OS), at the cost of significant side-effects. We hypothesized that "augmented RT" schedules (defined as either dose-escalation on the prostate gland over 78 Gy and/or addition of whole pelvic radiotherapy (WPRT)), combined with long-term ADT can reach excellent prostate cancer specific survival (PCSS) in this population with little detrimental impact on quality of life.

METHODS

We searched Pubmed database until February 8, 2024. Studies reporting both oncological and toxicity outcomes after "augmented RT" were deemed eligible. Studies without ADT or with ARPI intensification were deemed ineligible.

RESULTS

Dose-escalation within the prostate gland at doses over 78 Gy halved the risk of biochemical recurrence at 5 years, with however no impact on PCSS. The addition of WPRT provides a 5-year disease-free survival (DFS) reaching 89.5 % at 5 years, with no significant increase in late grade≥ 2 genito-urinary (GU) or gastrointestinal (GI) toxicity. Combined approaches result in 9-year PCSS ranging between 96.1 % and 100 %. Most approaches demonstrated excellent safety profiles.

CONCLUSIONS

"Augmented RT" reached excellent oncological outcomes, with minimal additional toxicity. The development of biomarkers might lead to further treatment personalization, in the rapidly evolving landscape of systemic therapies.

Urethra-sparing prostate cancer radiotherapy: Current practices and future insights from an international survey

Purpose

In prostate cancer patients, high radiation doses to the urethra have been associated with an increased risk of severe genitourinary toxicity following dose-escalated radiotherapy. Urethra-sparing techniques have emerged as a promising approach to reduce urinary toxicity. This international survey aims to evaluate current global practices in urethra-sparing and explore future directions for the implementation of this technique in external beam radiotherapy (EBRT) for prostate cancer.

Methods and materials

In April 2024, a survey consisting of 20 questions was distributed to 26 international radiation oncology experts in prostate cancer EBRT, with 23 experts participating. The survey focused on clinical scenarios which might take benefit from urethra-sparing, the definition of the urethra and urinary organs-at-risk, and urethral dose constraints.

Results

Magnetic resonance imaging with T2-weighted sequences is the preferred method for urethra contouring (83 % consensus). Based on the experts opinion, urethra-sparing should be considered for prostate cancer EBRT, regardless of pelvic irradiation, except in cases where the tumor is located within 2 mm of the urethra and/or transitional zone, or in T4 disease. Most experts would not apply specific dose constraints to the urethra for either conventional or moderate hypofractionation regimens. When delivering stereotactic body radiotherapy (SBRT), urethra-sparing with dose hotspot limitation (urethra steering) is recommended by 70 % of the experts, in particular when combined with focal boosting (91 %). Urethra dose-reduction is also the favored approach for salvage prostate reirradiation with SBRT (70 % agreement). Large variations exists regarding urethral dose constraints.

Conclusions

Urethra-sparing is a promising technique for the mitigation of urinary toxicity in prostate cancer patients undergoing EBRT, particularly recommended for ultra-hypofractionation and reirradiation with SBRT. The lack of consensus on specific urethral dose constraints and optimal sparing techniques underscores the need for further research to standardize practices in this field.

Geometric and dosimetric evaluation of CTV contour adaptations by radiation therapists for adaptive prostate radiotherapy on a 0.35 T MR-Linac

Background & purpose

Magnetic resonance guided adaptive radiotherapy (MRgART) enables hypofractionated prostate radiotherapy by daily contour adaptation. The MRgART workflow, however, is labour intensive and in many institutes still requires the presence of the radiation oncologist (RO). Transferring the online contour adaptation task to the radiation therapist (RTT) will release the clinician from attending each treatment fraction making MRgRT more efficient and cost effective. In this study we investigate the viability of RTT-led prostate MRgART on a low-field MR-linac, by assessing the interobserver variations of RTT- and RO-generated CTV contour adaptations as well as the resulting dosimetric effects.

Materials & methods

Four RTTs and four ROs performed CTV contour adaptations on first fraction data in ten patients. Delineations were compared against a gold standard contour using target volume, Dice similarity coefficient (DSC), and 95th percentile Hausdorff distance. In addition, a dosimetric evaluation was performed on all first fractions by performing plan adaptations based on all RTT contour adaptation and comparing these to the clinically delivered plan. Finally, a full-treatment simulation was performed in four patients to investigate the dosimetric effects of the RTTs' contour adaptations throughout an entire treatment.

Results

RTTs with no experience in prostate delineation prior to this study spent more time on CTV contour adaptations. The geometric and dosimetric analyses, however, showed no statistically significant differences between both groups.

Conclusions

This study confirmed that RTTs perform similarly to ROs in carrying out online contour adaptations. These results indicate the feasibility of initiating a transition in contour adaptation tasks from ROs to RTTs.

The interplay between acute and late toxicity among patients receiving prostate radiotherapy: an individual patient data meta-analysis of six randomised trials

BACKGROUND

The association between acute and late toxicity following prostate radiotherapy has not been well studied using data from multiple randomised clinical trials and fractionation schedules. We aimed to characterise the relationship between acute and late genitourinary and gastrointestinal toxicity among patients receiving conventionally fractionated or moderately hypofractionated prostate radiotherapy.

METHODS

This was an individual patient data meta-analysis that identified randomised phase 3 trials of conventionally fractionated or moderately hypofractionated prostate radiotherapy in the Meta-Analysis of Randomized trials in Cancer of the Prostate (MARCAP) Consortium that had individual-level acute and late toxicity data available and were available before Dec 1, 2023. Trials without individual patient data were excluded. Data were provided to MARCAP by study investigators. The associations between acute (≤3 months after radiotherapy) and late (>3 months after radiotherapy) grade 2 or greater genitourinary and gastrointestinal toxicities were assessed using adjusted generalised linear mixed models (adjusted for age, androgen deprivation therapy status, type of radiotherapy, radiation dose, and radiation schedule). In the subset of trials that collected Expanded Prostate Cancer Index Composite quality of life (QOL) evaluations, the association between acute genitourinary and gastrointestinal toxicity and decrements at least twice the minimal clinically important difference (MCID) for urinary and bowel QOL were also evaluated.

FINDINGS

Six of 26 available trials met all the eligibility criteria. 6593 patients were included (conventionally fractionated: n=4248; moderately hypofractionated: n=2345). Median follow-up was 72 months (IQR 61-94). Acute grade 2 or greater genitourinary toxicity was associated with both late grade 2 or greater genitourinary toxicity (odds ratio 2·20 [95% CI 1·88-2·57], p<0·0001) and decrement at least twice the MCID in urinary QOL (1·41 [1·17-1·68], p=0·0002). Acute grade 2 or greater gastrointestinal toxicity was associated with both late grade 2 or greater gastrointestinal toxicity (2·53 [2·07-3·08], p<0·0001) and decrement at least twice the MCID in bowel QOL (1·52 [1·26-1·83], p<0·0001).

INTERPRETATION

Acute toxicity following prostate radiotherapy was statistically significantly associated with late toxicity and with decrement in patient-reported QOL metrics. These data support efforts to evaluate whether interventions that reduce acute toxicity ultimately reduce the risk of late toxicity.

FUNDING

National Institutes of Health and US Department of Defense.

Two-fraction Versus Five-fraction Stereotactic Body Radiotherapy for Intermediate-risk Prostate Cancer: The TOFFEE Meta-analysis of Individual Patient Data from Four Prospective Trials

BACKGROUND AND OBJECTIVE

Recent randomized controlled trials have demonstrated the efficacy of five-fraction stereotactic body radiotherapy (5F-SBRT) for prostate cancer (PC), but there is no comparative evidence for fewer fractions. We compare outcomes of prostate two-fraction SBRT (2F-SBRT) and 5F-SBRT using prospective data for patients with intermediate-risk (IR) PC.

METHODS

This meta-analysis of individual patient data evaluated IR-PC from four prospective trials of prostate SBRT (two trials each of 2F- and 5F-SBRT). The primary endpoint was the cumulative incidence of biochemical failure (BCF). Secondary endpoints included the cumulative incidence of distant metastases (DM) and patient-reported quality of life (QoL).

KEY FINDINGS AND LIMITATIONS

Of the 199 patients meeting the eligibility criteria, 143 (72%) were in the 5F-SBRT group and 56 (28%) were in the 2F-SBRT group. Median follow-up was 9.4 years. There was no significant difference in BCF with a 5-year cumulative incidence of 3.6% (95% CI 0-8.6%) in the 2F-SBRT group and 6.0% (95% CI 1.8-10.2%) in the 5F-SBRT group (p = 0.73). There was no significant difference in DM incidence. We found no differences in acute and late urinary or bowel QoL. Limitations include the non-randomized comparison.

CONCLUSIONS AND CLINICAL IMPLICATIONS

We report the first prospective comparison of prostate 2F-SBRT and 5F-SBRT. We found no significant difference in efficacy, or in urinary or bowel QoL. This meta-analysis further encourages the potential of 2F-SBRT to be a standard-of-care option for IR PC.

Quality of Decision Making in Radiation Oncology

High-quality decision making in radiation oncology requires the careful consideration of multiple factors. In addition to the evidence-based indications for curative or palliative radiotherapy, this article explores how, in routine clinical practice, we also need to account for many other factors when making high-quality decisions. Foremost are patient-related factors, including preference, and the complex interplay between age, frailty and comorbidities, especially with an ageing cancer population. Whilst clinical practice guidelines inform our decisions, we need to account for their applicability in different patient groups and different resource settings. With particular reference to curative-intent radiotherapy, we explore decisions regarding dose fractionation schedules, use of newer radiotherapy technologies and multimodality treatment considerations that contribute to personalised patient-centred care.

Cargo Cult Radiotherapy: The Illusion of Precision in Advanced Technologies

Emerging radiotherapy technologies such as proton therapy, MR-guided radiotherapy, and real-time adaptive radiotherapy share a common goal of improving radiotherapy outcomes by increasing the anatomic precision of treatment delivery. In this piece, we provide a critical view of "precision radiotherapy" by examining the assumptions underlying the theory and practice of these techniques. Our goal was not to provide an exhaustive review of published literature; rather, we strove to write an accessible and thought-provoking article that would challenge conventional wisdom and stimulate further discussion and debate.

Embracing the Future of Clinical Trials in Radiation Therapy: An NRG Oncology CIRO Technology Retreat Whitepaper on Pioneering Technologies and AI-Driven Solutions

This white paper examines the potential of pioneering technologies and artificial intelligence-driven solutions in advancing clinical trials involving radiation therapy. As the field of radiation therapy evolves, the integration of cutting-edge approaches such as radiopharmaceutical dosimetry, FLASH radiation therapy, image guided radiation therapy, and artificial intelligence promises to improve treatment planning, patient care, and outcomes. Additionally, recent advancements in quantum science, linear energy transfer/relative biological effect, and the combination of radiation therapy and immunotherapy create new avenues for innovation in clinical trials. The paper aims to provide an overview of these emerging technologies and discuss their challenges and opportunities in shaping the future of radiation oncology clinical trials. By synthesizing knowledge from experts across various disciplines, this white paper aims to present a foundation for the successful integration of these innovations into radiation therapy research and practice, ultimately enhancing patient outcomes and revolutionizing cancer care.

Prostate motion in magnetic resonance imaging-guided radiotherapy and its impact on margins

PURPOSE

This study focused on reducing the margin for prostate cancer treatment using magnetic resonance imaging-guided radiotherapy by investigating the intrafractional motion of the prostate and different motion-mitigation strategies.

METHODS

We retrospectively analyzed intrafractional prostate motion in 77 patients with low- to intermediate-risk prostate cancer treated with five fractions of 7.25 Gy on a 1.5 T magnetic resonance linear accelerator. Systematic drift motion was observed and described by an intrafractional motion model. The planning target volume (PTV) margin was calculated in a cohort of 77 patients and prospectively evaluated for geometric coverage in a separate cohort of 24 patients.

RESULTS

The intrafractional model showed that the prostate position starts out of equilibrium for the anterior-posterior (-1.8 ± 3.1 mm) and superior-inferior (1.7 ± 2.6 mm) directions, with relaxation times of 12 and 15 min, respectively. Position verification scans are acquired at 30 min on average. At that time, the transient drift motion becomes indistinguishable from the residual random intrafractional motion. PTV margins can be reduced to 1.8 mm (left-right), 3.2 mm (anterior-posterior), and 2.9 mm (superior-inferior). Evaluation of the overlap with the clinical target volume (CTV) was performed for a total of 120 fractions of 24 patients. The overlap range between the CTV and the PTV was 93-100% and the applied 3‑mm PTV margin for the CTV had a 99.5% averaged geometric overlap for all patients.

CONCLUSION

A PTV margin reduction to 3 mm is feasible. A patient-specific approach could reduce the margins further.

Evolving Trends and Patterns of Utilization of Magnetic Resonance-Guided Radiotherapy at a Single Institution, 2018-2024

Background/Objectives: Over the past decade, significant advances have been made in image-guided radiotherapy (RT) particularly with the introduction of magnetic resonance (MR)-guided radiotherapy (MRgRT). However, the optimal clinical applications of MRgRT are still evolving. The intent of this analysis was to describe our institutional MRgRT utilization patterns and evolution therein, specifically as an early adopter within a center endowed with multiple other technology platforms. Materials/Methods: We retrospectively evaluated patterns of MRgRT utilization for patients treated with a 0.35-Tesla MR-Linac at our institution from April 2018 to April 2024. We analyzed changes in utilization across six annualized periods: Period 1 (April 2018-April 2019) through Period 6 (April 2023-April 2024). We defined ultra-hypofractionation (UHfx) as 5 or fewer fractions with a minimum fractional dose of 5 Gy. Electronic health records were reviewed, and data were extracted related to patient, tumor, and treatment characteristics. Results: A total of 823 treatment courses were delivered to 712 patients treated for 854 lesions. The most commonly treated sites were the pancreas (242 [29.4%]), thorax (172; 20.9%), abdominopelvic lymph nodes (107; 13.0%), liver (72; 8.7%), and adrenal glands (68; 8.3%). The median total prescribed dose of 50 Gy in five fractions (fxs) was typically delivered in consecutive days with automatic beam gating in inspiration breath hold. The median biologically effective dose (α/β = 10, BED10) was 94.4 Gy with nearly half (404, 49.1%) of all courses at a prescribed BED10 ≥ 100 Gy, which is widely regarded as a highly effective ablative dose. Courses in Period 6 vs. Period 1 more often had a prescribed BED10 ≥ 100 Gy (60.2% vs. 41.6%; p = 0.004). Of the 6036 total delivered fxs, nearly half (2643, 43.8%) required at least one fx of on-table adaptive radiotherapy (oART), most commonly for pancreatic tumors (1081, 17.9%). UHfx was used in over three quarters of all courses (630, 76.5%) with 472 (57.4%) of these requiring oART for at least one fraction. The relative utilization of oART increased significantly from Period 1 to Period 6 (37.6% to 85.0%; p < 0.001); a similar increase in the use of UHfx (66.3% to 89.5%; p < 0.001) was also observed. The median total in-room time for oART decreased from 81 min in Period 1 to 45 min in Period 6, while for non-oART, it remained stable around 40 min across all periods. Conclusions: Our institution implemented MRgRT with a priority for targeting mobile extracranial tumors in challenging anatomic locations that are frequently treated with dose escalation, require enhanced soft-tissue visualization, and could benefit from an ablative radiotherapy approach. Over the period under evaluation, the use of high-dose ablative doses (BED10 ≥ 100 Gy), oART and UHfx (including single-fraction ablation) increased significantly, underscoring both a swift learning curve and ability to optimize processes to maximize throughput and efficiency.

Ongoing prospective studies on reirradiation: A systematic review of a clinical trials database

INTRODUCTION

Reirradiation has gained increasing interest, as advances in systemic therapy increase the survival of patients with cancer, and modern radiation techniques allow more precise treatments. However, high-quality prospective evidence on the safety and efficacy of reirradiation to guide clinical practice remains scarce. This systematic review evaluates ongoing prospective studies on reirradiation to identify research gaps and priorities.

METHODS

A systematic review of ClinicalTrials.gov was conducted on July 11, 2024, using search terms related to reirradiation. Inclusion criteria were prospective studies that were "recruiting," "not yet recruiting," or "active, not recruiting." Studies with published results, retrospective, and in-silico studies were excluded. The review followed PRISMA 2020 guidelines and recommendations for systematic searches of clinical trial registries.

RESULTS

Among 1026 identified studies, 307 were screened, 99 were included. Fourty (40%) focused on central nervous system (CNS), 23 (23%) head and neck, and 17 (17%) on pelvic reirradiation. Most studies (90%) were interventional, with 32 (32%) phase II and 4 (4%) phase III trials. Sixteen trials were randomized (RCTs), including the 4 phase III trials for recurrent glioblastoma, rectal and nasopharyngeal cancer. Ten dose escalation trials focus on recurrent prostate, rectal, and non-small cell lung cancer as well as glioma. Modern high-precision radiotherapy techniques were frequently used, with 21 (21%) studies using stereotactic radiotherapy and 17 (17%) using particle therapy. Combinations with systemic therapies were investigated in 41 (41%) studies.

CONCLUSION

Ongoing studies most frequently focus on CNS, head and neck, and pelvic reirradiation. There remains a critical need for RCTs, in particular for lung, breast, and gynecological cancers. Dose escalation trials, application of precision radiation techniques and combinations with modern systemic therapy may help define the optimal multimodality treatment schedules.

A deep learning algorithm to generate synthetic computed tomography images for brain treatments from 0.35 T magnetic resonance imaging

Background and Purpose

The development of Magnetic Resonance Imaging (MRI)-only Radiotherapy (RT) represents a significant advancement in the field. This study introduces a Deep Learning (DL) algorithm designed to quickly generate synthetic CT (sCT) images from low-field MR images in the brain, an area not yet explored.

Methods

Fifty-six patients were divided into training (32), validation (8), and test (16) groups. A conditional Generative Adversarial Network (cGAN) was trained on pre-processed axial paired images. sCTs were validated using mean absolute error (MAE) and mean error (ME) calculated within the patient body. Intensity Modulated Radiation Therapy (IMRT) plans were optimised on simulation MRI and calculated considering sCT and original CT as electron density (ED) map. Dose distributions using sCT and CT were compared using global gamma analysis at different tolerance criteria (2 %/2mm and 3 %/3mm) and evaluating the difference in estimating different Dose Volume Histogram (DVH) parameters for target and organs at risk (OARs).

Results

The network generated sCTs of each single patient in less than two minutes (mean time = 103 ± 41 s). For test patients, the MAE was 62.1 ± 17.7 HU, and the ME was -7.3 ± 13.4 HU. Dose parameters on sCTs were within 0.5 Gy of those on original CTs. Gamma passing rates 2 %/2mm, and 3 %/3mm criteria were 99.5 %±0.5 %, and 99.7 %±0.3 %, respectively.

Conclusion

The proposed DL algorithm generates in less than 2 min accurate sCT images in the brain for online adaptive radiotherapy, potentially eliminating the need for CT simulation in MR-only workflows for brain treatments.

MR-Guided Adaptive Radiotherapy in Localized Prostate Cancer

MR-guided radiotherapy (MRgRT) is novel treatment modality in Radiation Oncology that could allow a higher precision and tolerability of Radiation Treatments. This modality is possible due to dedicated systems consisting of a MR scanner mounted on a conventional linac and software that permit daily online treatment plan adaptation. Prostate cancer (PC) is one of the most common malignancies in RO clinical practice and currently under investigation with this new technology. The focus of this review is to describe the current state of the art and clinical results of MRgRT in the treatment of PC. The available technology are briefly described, as well as the published literature and possible future applications.

Acute Toxicity and Early Prostate Specific Antigen Response After Two-Fraction Stereotactic Radiation Therapy for Localized Prostate Cancer Using Peri-Rectal Spacing-Initial Report of the SABR-Dual Trial

PURPOSE

SABR-Dual is a phase-III trial with an initial phase-I safety cohort, of 2-fraction stereotactic radiotherapy (SABR) with optional magnetic resonance imaging (MRI)-based focal boost, using peri-rectal spacing, for localized prostate cancer. This represents the initial report from the phase-I non-randomized cohort.

METHODS AND MATERIALS

Subjects had favorable intermediate risk (FIR) or low risk prostate adenocarcinoma, and gland volume <80 cc. All underwent radiopaque hydrogel spacer and fiducial marker placement before simulation (computed tomography and 3-tesla T2 MRI). The clinical target volume included the entire prostate, and in FIR patients, 1-2 cm of seminal vesicle. A 2-mm expansion was applied for planning target volume (PTV), and a dose of 27 Gy was prescribed to the PTV-prostate, 23 Gy to the PTV-seminal vesicle, with an optional 30 Gy simultaneous boost to an MRI-defined dominant lesion. Primary endpoint was 3-month patient-reported changes in quality of life based on the Expanded Prostate Cancer Index Composite-26, International Prostate Symptom Score, and Sexual Health Inventory for Men questionnaires. Secondary endpoints were 6-month quality of life, acute toxicity (using Common Terminology Criteria for Adverse Events version 5.0) and early Prostate specific antigen (PSA) response.

RESULTS

Among the 20 patients in the phase-I cohort, 95% had FIR disease, and 50% received a simultaneous boost. At median follow-up of 8 months, a 3-month minimally clinically important change occurred in 1/20 (5%), 6/20 (30%), 2/20 (10%), 4/20 (20%), and 5/20 (25%) in urinary incontinence, urinary obstructive, bowel, sexual, and hormonal domains. There was a mean increase of 1 ± 5.4 in International Prostate Symptom Score and decrease of 1.8 ± 6.5 in Sexual Health Inventory for Men scores. Rates of grade 2 urinary and bowel toxicity were 10% and 0%, respectively, with no grade ≥3 toxicities. Mean PSA decrease at last follow-up was 70.4% ± 17.7%.

CONCLUSION

This generalizable protocol of 2-fraction prostate SABR using peri-rectal spacing is a safe approach for ultra-hypofractionated dose-escalation, with minimal acute toxicity. Longer-term outcomes and direct comparison with standard 5-fraction SABR are being studied in the phase-III randomized portion of SABR-Dual.

Ablative Radiation Therapy for Unfavorable Prostate Tumors (ABRUPT): Preliminary Analysis of Toxicity and Quality of Life from a Prospective Study

PURPOSE

To assess late gastrointestinal (GI) and genitourinary (GU) side effects in patients with organ-confined unfavorable prostate cancer (PCa) treated with single-dose ablative radiation therapy (SDRT).

METHODS AND MATERIALS

Thirty patients enrolled in a single-arm prospective trial received 24 Gy SDRT to the whole prostate with urethra-sparing and organ motion control delivered on a Linac platform with a 10 MV flattening filter-free single partial arc. Androgen deprivation therapy was prescribed as per standard of care. Treatment-related acute and late GU and GI toxicities (Common Terminology Criteria for Adverse Events_v5 scale) and quality of life (QoL) outcomes (European Organisation for Research and Treatment of Cancer [EORTC] QLQ-PR25/C30, International Prostate Symptom Score [IPSS]) were assessed at different time points. Minimal important difference (MID) was established as a change of >0.5 pooled standard deviations from baseline. Statistical analysis included analysis of variance and logistic regression.

RESULTS

Median follow-up was 18 months (range, 6-31 months), with no ≥G3 late side effects observed. G2 late GI and G2 late GU toxicities occurred in 1 and 2 patients, respectively. GI toxicity of any grade correlated with maximum rectal dose (P = .021). Lower baseline QoL score (P = .025), higher baseline IPSS score (P = .049), acute GU toxicity (P = .029), and acute urinary domain MID (P = .045) predicted GU toxicity of any grade. In multivariate analysis (MVA), only baseline QoL score (odds ratio [OR], 0.95, P = .031) and acute GU toxicity (OR, 8.4, P = .041) remained significant. Significant QoL change was observed only in the urinary domain (P = .005), with a median increase from 8 to 17. Late urinary MID correlated with acute urinary MID (P = .003), acute QoL MID (P = .029), acute GU toxicity (P = .030), and lower baseline urinary score (P = .033). In MVA, only acute urinary MID predicted late urinary MID (OR, 9.7, P = .035).

CONCLUSIONS

Our findings provide promising data on the feasibility and safety of 24 Gy whole-gland SDRT with urethra-sparing and organ motion control, in association with androgen deprivation therapy and an adequate prophylactic medication, in organ-confined unfavorable PCa. Long-term follow-up is needed to confirm these results.

Magnetic Resonance-Guided Stereotactic Radioablation for Septal Ventricular Tachycardias

BACKGROUND

Stereotactic arrhythmia radioablation (STAR) was introduced to treat ventricular tachycardia (VT) refractory to catheter ablation. No data are now available in the septal VT substrate setting, representing a challenge when using conventional techniques.

OBJECTIVES

This study sought to evaluate the arrhythmic burden in patients with septal VT treated with magnetic resonance-guided STAR (MRgSTAR).

METHODS

We enrolled consecutive patients with septal VT substrate. The therapy target was achieved by combining anatomic/functional and electrophysiologic information. Patients were treated with a single fraction of 25 Gy adopting MRgSTAR. All patients were clinically followed up, and all implantable cardiac devices were remotely monitored. The efficacy outcome included recurrences of any sustained VT beyond the 6-week blanking period after MRgSTAR. The safety outcome was the incidence of adverse events and atrioventricular block.

RESULTS

We included 11 patients with septal substrate VT (median age: 68 years; Q1-Q3: 64.5-78 years; 100% male). Clinical presentation was an electrical storm in 81.8% of patients. No complications occurred after MRgSTAR, and 6 (54.5%) patients were discharged on the same day of treatment. During a mean follow-up of 12 ± 6 months, the efficacy outcome occurred in 3 (27.3%) cases. A significative reduction of implantable cardioverter-defibrillator (ICD) therapy (23.6 before MRgSTAR vs 1.7 after MRgSTAR; P < 0.001) was observed. Left ventricular ejection fraction increased significantly after treatment (38% [Q1-Q3: 33.5%-42.0%] before MRgSTAR vs 43.8% [Q1-Q3: 35%-47%] after MRgSTAR; P = 0.04). No adverse effects were observed in the implantable cardioverter-defibrillator and lead system; in the 7 patients with preserved atrioventricular conduction, no atrioventricular block was reported.

CONCLUSIONS

MRgSTAR represents a safe and effective strategy for treating septal VT.

Radical Prostatectomy Versus Stereotactic Radiotherapy for Clinically Localised Prostate Cancer: Results of the PACE-A Randomised Trial

BACKGROUND AND OBJECTIVE

Randomised data on patient-reported outcomes (PROs) for stereotactic body radiotherapy (SBRT) and prostatectomy in localised prostate cancer are lacking. PACE-A compared patient-reported health-related quality of life after SBRT with that after prostatectomy.

METHODS

PACE is a phase 3 open-label, randomised controlled trial. PACE-A randomised men with low- to intermediate-risk localised prostate cancer to SBRT or prostatectomy (1:1). Androgen deprivation therapy (ADT) was not permitted. The coprimary outcomes were the Expanded Prostate Index Composite (EPIC-26) number of absorbent urinary pads required daily and bowel domain score at 2 yr. The secondary endpoints were clinician-reported toxicity, sexual functioning, and other PROs.

KEY FINDINGS AND LIMITATIONS

In total, 123 men were randomised (60 undergoing prostatectomy and 63 SBRT) from August 2012 to February 2022. The median follow-up time was 60.7 mo. The median age was 65.5 yr and the median prostate-specific antigen (PSA) value 7.9 ng/ml; 92% had National Comprehensive Cancer Network (NCCN) intermediate-risk disease. Fifty participants received prostatectomy and 60 received SBRT. At 2 yr, 16/32 (50%) prostatectomy and three of 46 (6.5%) SBRT participants used one or more urinary pads daily (p < 0.001; 15 and two, respectively, used one pad daily); the estimated difference was 43% (95% confidence interval [CI]: 25%, 62%). At 2 yr, bowel scores were better for prostatectomy (median [interquartile range] 100 [100-100]) than for SBRT (87.5 [79.2-100]; p < 0.001), with an estimated mean difference of 8.9 between these (95% CI: 4.2, 13.7); sexual scores were worse for prostatectomy (18 [13.8-40.3]) than for SBRT (62.5 [32.0-87.5]). The limitations were slow recruitment and incomplete 2-yr PRO response rates.

CONCLUSIONS AND CLINICAL IMPLICATIONS

SBRT was associated with less patient-reported urinary incontinence and sexual dysfunction, and slightly more bowel bother than prostatectomy. These randomised data should inform treatment decision-making for patients with localised, intermediate-risk prostate cancer.

Upper Urinary Tract Stereotactic Body Radiotherapy Using a 1.5 Tesla Magnetic Resonance Imaging-Guided Linear Accelerator: Workflow and Physics Considerations

Background/Objectives: Advancements in radiotherapy technology now enable the delivery of ablative doses to targets in the upper urinary tract, including primary renal cell carcinoma (RCC) or upper tract urothelial carcinomas (UTUC), and secondary involvement by other histologies. Magnetic resonance imaging-guided linear accelerators (MR-Linacs) have shown promise to further improve the precision and adaptability of stereotactic body radiotherapy (SBRT). Methods: This single-institution retrospective study analyzed 34 patients (31 with upper urinary tract non-metastatic primaries [RCC or UTUC] and 3 with metastases of non-genitourinary histology) who received SBRT from August 2020 through September 2024 using a 1.5 Tesla MR-Linac system. Treatment plans were adjusted by using [online settings] for "adapt-to-position" (ATP) and "adapt-to-shape" (ATS) strategies for anatomic changes that developed during treatment; compression belts were used for motion management. Results: The median duration of treatment was 56 min overall and was significantly shorter using the adapt-to-position (ATP) (median 54 min, range 38-97 min) in comparison with adapt-to-shape (ATS) option (median 80, range 53-235 min). Most patients (77%) experienced self-resolving grade 1-2 acute radiation-induced toxicity; none had grade ≥ 3. Three participants (9%) experienced late grade 1-2 toxicity, potentially attributable to SBRT, with one (3%) experiencing grade 3. Conclusions: We conclude that MR-Linac-based SBRT, supported by online plan adaptation, is a feasible, safe, and highly precise treatment modality for the definitive management of select upper urinary tract lesions.

Magnetic Resonance Imaging Versus Computed Tomography Guidance for Stereotactic Body Radiotherapy in Prostate Cancer: 2-year Outcomes from the MIRAGE Randomized Clinical Trial

It has been shown that magnetic resonance imaging (MRI) guidance versus computed tomography (CT) guidance for aggressive margin-reduction (AMR) for stereotactic body radiotherapy (SBRT) in prostate cancer reduces acute toxicity, but the longer-term benefits are unknown. We performed a secondary analysis of MIRAGE, a phase 3 randomized clinical trial of MRI-guided SBRT for prostate cancer, to determine whether AMR with MRI guidance significantly reduced 2-yr physician-scored or patient-reported toxic effects in comparison to CT guidance. The cumulative incidence of 2-yr physician-scored toxicity, defined as grade ≥2 genitourinary (GU) and gastrointestinal (GI) toxic effects according to Common Terminology Criteria for Adverse Events v4.03, were lower with MRI guidance. Cumulative incidence rates of late grade ≥2 toxicity at 2 yr with MRI-guided versus CT-guided SBRT were 27% (95% confidence interval [CI] 19-39%)] versus 51% (95% CI 41-63%) for GU toxicity (p = 0.004), and 1.4% (95% CI 0.2-9.6) versus 9.5% (95% CI 4.6-19) for GI toxicity (p = 0.025). Cumulative logistic regression revealed that MRI-guided SBRT was associated with significantly lower odds of a clinically relevant deterioration in bowel function according to the Expanded Prostate Cancer Index Composite-26 score (odds ratio 0.444, 95% CI 0.209-0.942; p = 0.035) and in the Sexual Health Inventory in Men score (odds ratio 0.366, 95% CI 0.148-0.906; p = 0.03). There were no significant differences in the odds of a deterioration for other quality-of-life metrics. These findings support the hypothesis that aggressive planning for margin reduction for prostate SBRT using MRI leads to continued reductions in toxic effects over 2-yr follow-up. This trial is registered on ClinicalTrials.gov Identifier as NCT04384770.

Defining the potential for sexual structures-sparing for prostate cancer external beam radiotherapy: A dosimetric study

PURPOSE

The purpose of the study was to evaluate the dosimetric impact of sexual-sparing radiotherapy for prostate cancer, with magnetic resonance-only treatment planning.

MATERIAL AND METHODS

Fifteen consecutive patients receiving prostate cancer radiotherapy were selected. A synthetic CT was generated with a deep learning method from each T2-weighted MRI performed at the time of treatment planning. For each patient, two plans were performed: standard treatment planning and sexual-structures sparing treatment planning. The treatment plan was designed to deliver a dose of 78Gy to the prostate and 50Gy to the seminal vesicles in 2Gy daily fractions, using volumetric arc therapy. Dose-volume histograms were computed to compare treatment plans.

RESULTS

All plans fulfilled dosimetric objectives and were equivalent regarding planning target volume coverage. The doses delivered to both rectum, bladder, and femoral heads were similar between plans (P=0.20). Sexual-sparing plans enabled to decrease all dosimetric parameters on sexual organs-at-risk. The mean penile bulb dose in sexual-sparing plans was significantly reduced (21.1Gy±20.7 versus 13.4Gy±14.0, P<0.01), however with large variability observed between individuals. The mean dose delivered to the corpora cavernosa was also significantly reduced within sexual-sparing plans (13.1Gy±16.7 versus 8.6Gy±10.4, P<0.01). A significant reduction was also observed in the highest doses delivered to internal pudendal arteries (D10%: 48.4Gy±8.3 versus 33.1Gy±4.6, P<0.05; D5%: 52.0Gy±8.7 versus 36.8Gy±5.5, P<0.05).

CONCLUSION

Sparing of sexual structures appears feasible, without compromising neither planning target volume coverage nor doses delivered to non-sexual organs at risk. The clinical significance of this dose-reduction requires prospective evaluation.

Current State of Stereotactic Body Radiation Therapy for Genitourinary Malignancies

ABSTRACT

Stereotactic body radiation therapy (SBRT) involves the delivery of high-dose, highly precise radiation therapy to focal sites of gross tumor involvement. Recent advances in radiation planning and image guidance have facilitated rapid growth in the evidence for and use of SBRT, particularly for genitourinary malignancies, where the underlying radiobiology often suggests greater tumor sensitivity to SBRT than to conventionally fractionated radiation. Here, we review the evolution of SBRT for patients with prostate adenocarcinoma and renal cell carcinoma. We discuss state-of-the-art trials, indications, and future directions in the SBRT-based management of both localized and metastatic disease. With rapidly growing enthusiasm and evidence, clinical and translational research efforts on the biology and outcomes of SBRT over the coming decade will be crucial to refining the indications, technical approach, and synergistic combinations of SBRT with highly active systemic therapies and improve the efficacy and quality-of-life outcomes for patients with genitourinary malignancies.

Open-source hardware and software for the measurement, characterization, reporting, and correction of geometric distortion in MRI

BACKGROUND

Geometric distortion is a serious problem in MRI, particularly in MRI guided therapy. A lack of affordable and adaptable tools in this area limits research progress and harmonized quality assurance.

PURPOSE

To develop and test a suite of open-source hardware and software tools for the measurement, characterization, reporting, and correction of geometric distortion in MRI.

METHODS

An open-source python library was developed, comprising modules for parametric phantom design, data processing, spherical harmonics, distortion correction, and interactive reporting. The code was used to design and manufacture a distortion phantom consisting of 618 oil filled markers covering a sphere of radius 150 mm. This phantom was imaged on a CT scanner and a novel split-bore 1.0 T MRI magnet. The CT images provide distortion-free dataset. These data were used to test all modules of the open-source software.

RESULTS

All markers were successfully extracted from all images. The distorted MRI markers were mapped to undistorted CT data using an iterative search approach. Spherical harmonics reconstructed the fitted gradient data to 1.0 ± 0.6% of the input data. High resolution data were reconstructed via spherical harmonics and used to generate an interactive report. Finally, distortion correction on an independent data set reduced distortion inside the DSV from 5.5 ± 3.1 to 1.6 ± 0.8 mm.

CONCLUSION

Open-source hardware and software for the measurement, characterization, reporting, and correction of geometric distortion in MRI have been developed. The utility of these tools has been demonstrated via their application on a novel 1.0 T split bore magnet.

The impact of rectal spacers in MR-guided adaptive radiotherapy

Background and purpose

The use of stereotactic ablative radiotherapy (SABR) for prostate cancer has increased significantly. However, SABR can elevate the risk of moderate gastrointestinal (GI) side effects. Rectal spacers mitigate this risk by reducing the rectal dose. This study evaluates the impact of rectal spacers in MR-guided adaptive radiotherapy (MRgART) for prostate SABR.

Materials and methods

A retrospective analysis was conducted on twenty patients with localised prostate cancer treated on the Unity MR-Linac at a single centre. Half of the cohort (n = 10) had rectal spacers placed before treatment. The adapt-to-shape strategy was used for online MRgART, and non-adapted plans were later generated offline for comparison. Dosimetric assessments were made between spacer and no-spacer cohorts, and between online adapted and non-adapted plans. Clinician-reported outcomes for genitourinary (GU) and GI toxicity were assessed at 3-, 6-, and 12-months post-treatment using Common Terminology Criteria for Adverse Events v.5.0.

Results

No grade 2 or higher toxicity was observed in either cohort. Overall, the dosimetric analysis showed comparable results between the cohorts for target volumes, with D95% of 36.3 Gy in the spacer cohort and 36.0 Gy in the no-spacer cohort (p = 0.08). The spacer cohort demonstrated significant benefits in all rectal dose objectives (p < 0.0001) and in some bladder objectives (V40, p = 0.03; V36, p = 0.03). Failure rates for achieving planning objectives were similar between spacer and no-spacer groups for online adapted plans, with most rates ranging from 0 % to 4 % in both groups.

Conclusion

The findings from this cohort suggest that MRgART is safe and effective for prostate SABR, with comparable toxicity rates in both spacer and no-spacer cohorts. While rectal spacers offer dosimetric advantages, the adaptive nature of MRgART can mitigate some dosimetric disparities, potentially reducing the need for invasive spacer placement. However, further studies with larger patient populations are needed to confirm these results.

Target Volume Optimization for Localized Prostate Cancer

PURPOSE

To provide a comprehensive review of the means by which to optimize target volume definition for the purposes of treatment planning for patients with intact prostate cancer with a specific emphasis on focal boost volume definition.

METHODS

Here we conduct a narrative review of the available literature summarizing the current state of knowledge on optimizing target volume definition for the treatment of localized prostate cancer.

RESULTS

Historically, the treatment of prostate cancer included a uniform prescription dose administered to the entire prostate with or without coverage of all or part of the seminal vesicles. The development of prostate magnetic resonance imaging (MRI) and positron emission tomography (PET) using prostate-specific radiotracers has ushered in an era in which radiation oncologists are able to localize and focally dose-escalate high-risk volumes in the prostate gland. Recent phase 3 data has demonstrated that incorporating focal dose escalation to high-risk subvolumes of the prostate improves biochemical control without significantly increasing toxicity. Still, several fundamental questions remain regarding the optimal target volume definition and prescription strategy to implement this technique. Given the remaining uncertainty, a knowledge of the pathological correlates of radiographic findings and the anatomic patterns of tumor spread may help inform clinical judgement for the definition of clinical target volumes.

CONCLUSION

Advanced imaging has the ability to improve outcomes for patients with prostate cancer in multiple ways, including by enabling focal dose escalation to high-risk subvolumes. However, many questions remain regarding the optimal target volume definition and prescription strategy to implement this practice, and key knowledge gaps remain. A detailed understanding of the pathological correlates of radiographic findings and the patterns of local tumor spread may help inform clinical judgement for target volume definition given the current state of uncertainty.

Adapting outside the box: Simulation-free MR-guided stereotactic ablative radiotherapy for prostate cancer

BACKGROUND AND PURPOSE

Magnetic resonance (MR)-guided radiotherapy (MRgRT) enhances treatment precision and adaptive capabilities, potentially supporting a simulation-free (sim-free) workflow. This work reports the first clinical implementation of a sim-free workflow using the MR-Linac for prostate cancer patients treated with stereotactic ablative radiotherapy (SABR).

MATERIALS AND METHODS

Fifteen patients who had undergone a prostate-specific membrane antigen positron emission tomography/CT (PSMA-PET/CT) scan as part of diagnostic workup were included in this work. Two reference plans were generated per patient: one using PSMA-PET/CT (sim-free plan) and the other using standard simulation CT (simCT plan). Dosimetric evaluations included comparisons between simCT, sim-free, and first fraction plans. Timing measurements were conducted to assess durations for both simCT and sim-free pre-treatment workflows.

RESULTS

All 15 patients underwent successful treatment using a sim-free workflow. Dosimetric differences between simCT, sim-free, and first fraction plans were minor and within acceptable clinical limits, with no major violations of standardised criteria. The sim-free workflow took on average 130 min, while the simCT workflow took 103 min.

CONCLUSION

This work demonstrates the feasibility and benefits of sim-free MR-guided adaptive radiotherapy for prostate SABR, representing the first reported clinical experience in an ablative setting. By eliminating traditional simulation scans, this approach reduces patient burden by minimising hospital visits and enhances treatment accessibility.

French AFU Cancer Committee Guidelines - Update 2024-2026: Prostate cancer - Diagnosis and management of localised disease

OBJECTIVE

The aim of the Oncology Committee of the French Urology Association is to propose updated recommendations for the diagnosis and management of localized prostate cancer (PCa).

METHODS

A systematic review of the literature from 2022 to 2024 was conducted by the CCAFU on the elements of diagnosis and therapeutic management of localized PCa, evaluating references with their level of evidence.

RESULTS

The recommendations set out the genetics, epidemiology and diagnostic methods of PCa, as well as the concepts of screening and early detection. MRI, the reference imaging test for localized cancer, is recommended before prostate biopsies are performed. Molecular imaging is an option for disease staging. Performing biopsies via the transperineal route reduces the risk of infection. Active surveillance is the standard treatment for tumours with a low risk of progression. Therapeutic methods are described in detail, and recommended according to the clinical situation.

CONCLUSION

This update of French recommendations should help to improve the management of localized PCa.

The role of MRI in radiotherapy planning: a narrative review "from head to toe"

Over the last few years, radiation therapy (RT) techniques have evolved very rapidly, with the aim of conforming high-dose volume tightly to a target. Although to date CT is still considered the imaging modality for target delineation, it has some known limited capabilities in properly identifying pathologic processes occurring, for instance, in soft tissues. This limitation, along with other advantages such as dose reduction, can be overcome using magnetic resonance imaging (MRI), which is increasingly being recognized as a useful tool in RT clinical practice. This review has a two-fold aim of providing a basic introduction to the physics of MRI in a narrative way and illustrating the current knowledge on its application "from head to toe" (i.e., different body sites), in order to highlight the numerous advantages in using MRI to ensure the best therapeutic response. We provided a basic introduction for residents and non-radiologist on the physics of MR and reported evidence of the advantages and future improvements of MRI in planning a tailored radiotherapy treatment "from head to toe". CRITICAL RELEVANCE STATEMENT: This review aims to help understand how MRI has become indispensable, not only to better characterize and evaluate lesions, but also to predict the evolution of the disease and, consequently, to ensure the best therapeutic response. KEY POINTS: MRI is increasingly gaining interest and applications in RT planning. MRI provides high soft tissue contrast resolution and accurate delineation of the target volume. MRI will increasingly become indispensable for characterizing and evaluating lesions, and to predict the evolution of disease.

Quality and Safety Considerations for Adaptive Radiation Therapy: An ASTRO White Paper

PURPOSE

Adaptive radiation therapy (ART) is the latest topic in a series of white papers published by the American Society for Radiation Oncology addressing quality processes and patient safety. ART widens the therapeutic index by improving the precision of radiation dose to targets, allowing for dose escalation and/or minimization of dose to normal tissue. ART is performed via offline or online methods; offline ART is the process of replanning a patient's treatment plan between fractions, whereas online ART involves plan adjustment with the patient on the treatment table. This is achieved with in-room imaging capable of assessing anatomic changes and the ability to reoptimize the treatment plan rapidly during the treatment session. Although ART has occurred in its simplest forms in clinical practice for decades, recent technological developments have enabled more clinical applications of ART. With increased clinical prevalence, compressed timelines, and the associated complexity of ART, quality and safety considerations are an important focus area.

METHODS

The American Society for Radiation Oncology convened an interdisciplinary task force to provide expert consensus on key workflows and processes for ART. Recommendations were created using a consensus-building methodology, and task force members indicated their level of agreement based on a 5-point Likert scale, from "strongly agree" to "strongly disagree." A prespecified threshold of ≥75% of raters selecting "strongly agree" or "agree" indicated consensus. Content not meeting this threshold was removed or revised.

SUMMARY

Establishing and maintaining an adaptive program requires a team-based approach, appropriately trained and credentialed specialists, significant resources, specialized technology, and implementation time. A comprehensive quality assurance program must be developed, using established guidance, to make sure all forms of ART are performed in a safe and effective manner. Patient safety when delivering ART is everyone's responsibility, and professional organizations, regulators, vendors, and end users must demonstrate a clear commitment to working together to deliver the highest levels of quality and safety.

Emerging and anticipated innovations in prostate cancer MRI and their impact on patient care

Prostate cancer (PCa) remains the leading malignancy affecting men, with over 3 million men living with the disease in the US, and an estimated 288,000 new cases and almost 35,000 deaths in 2023 in the United States alone. Over the last few decades, imaging has been a cornerstone in PCa care, with a crucial role in the detection, staging, and assessment of PCa recurrence or by guiding diagnostic or therapeutic interventions. To improve diagnostic accuracy and outcomes in PCa care, remarkable advancements have been made to different imaging modalities in recent years. This paper focuses on reviewing the main innovations in the field of PCa magnetic resonance imaging, including MRI protocols, MRI-guided procedural interventions, artificial intelligence algorithms and positron emission tomography, which may impact PCa care in the future.

When Best Care Takes a Back Seat to the Bottom Line

This Viewpoint discusses the clinical vs economic success of magnetic resonance imaging combined with linear accelerator technology and its impact on patients.

MRI-Linac-Based Radiotherapy-Promising or Hype?

This Viewpoint discusses the value of magnetic resonance imaging with linear accelerator (MRI-linac) technology, given the unmet needs in its development.

Prioritizing Patient-Centered Care in a World of Increasingly Advanced Technologies and Disconnected Care

With more treatment options in oncology lead to better outcomes and more favorable side effect profiles, patients are living longer-with higher quality of life-than ever, with a growing survivor population. As the needs of patients and providers evolve, and technology advances, cancer care is subject to change. This review explores the myriad of changes in the current oncology landscape with a focus on the patient perspective and patient-centered care.

Patient-Reported Outcomes Following Magnetic Resonance-Guided Radiation Therapy for Prostate Cancer: A Systematic Review and Meta-Analysis

PURPOSE

This systematic review provides an overview of literature on the impact of magnetic resonance-guided radiation therapy (MRgRT) on patient-reported outcomes (PROs) in patients with prostate cancer (PC).

METHODS AND MATERIALS

A systematic search was performed in October 2023 in PubMed, EMBASE, and Cochrane Library. The Patient, Intervention, Comparison, Outcomes, and Study design (PICOS) framework was used to determine eligibility criteria. Included were studies assessing PROs following MRgRT for PC with a sample size >10. Methodological quality was assessed using the Cochrane's Risk of Bias in Nonrandomized Studies - of Interventions and Cochrane's risk of bias tool for randomized trials. Relevant mean differences (MDs) compared with pre-RT were interpreted using minimal important differences. Meta-analyses were performed using random-effects models. Between-study heterogeneity was assessed using the I2 statistic.

RESULTS

Eleven observational studies and 1 randomized controlled trial (n = 897) were included. Nine studies included patients with primary PC with MRgRT as first-line treatment (n = 813) and 3 with MRgRT as second-line treatment (n = 84). Substantial risk of bias was found in 5 studies. European Organization for Research and Treatment Quality of Life Questionnaire (EORTC QLQ) core 30 (C30) and EORTC QLQ prostate cancer module (PR25) scores were pooled from 3 studies, and Expanded Prostate Cancer Index Composite (EPIC)-26 scores were pooled from 4 studies. Relevant MDs for the urinary domain were found with the EPIC-26 (MD, -10.0; 95% CI, -12.0 to -8.1; I2 = 0%) and the EORTC QLQ-PR25 (MD, 8.6; 95% CI, -4.7 to 22.0; I2 = 97%), both at end-RT to 1-month follow-up. Relevant MDs for the bowel domain were found with the EPIC-26 (MD, -4.7; 95% CI, -9.2 to -0.2; I2 = 82%) at end-RT or 1-month follow-up, but not with the EORTC QLQ-PR25. For both domains, no relevant MDs were found after 3 months of follow-up. No relevant MDs were found in the general quality of life domains of the EORTC QLQ C30.

CONCLUSIONS

MRgRT for PC results in a temporary worsening of patient-reported urinary and bowel symptoms during the first month after treatment compared with pre-RT, resolving at 3 months. No clinically relevant changes were found for general quality of life domains. These results provide important information for patient counseling and can serve as a benchmark for future studies.

Evaluation of knowledge-based planning models for male pelvic CBCT-based online adaptive radiotherapy on conventional linear accelerators

PURPOSE

To assess the practicality of employing a commercial knowledge-based planning tool (RapidPlan) to generate adapted intact prostate and prostate bed volumetric modulated arc therapy (VMAT) plans on iterative cone-beam computed tomography (iCBCT) datasets.

METHODS AND MATERIALS

Intact prostate and prostate bed RapidPlan models were trained utilizing planning data from 50 and 44 clinical cases, respectively. To ensure that refined models were capable of producing adequate clinical plans with a single optimization, models were tested with 50 clinical planning CT datasets by comparing dose-volume histogram (DVH) and plan quality metric (PQM) values between clinical and RapidPlan-generated plans. The RapidPlan tool was then used to retrospectively generate adapted VMAT plans on daily iCBCT images for 20 intact prostate and 15 prostate bed cases. As before, DVH and PQM metrics were utilized to dosimetrically compare scheduled (iCBCT Verify) and adapted (iCBCT RapidPlan) plans. Timing data was collected to further evaluate the feasibility of integrating this approach within an online adaptive radiotherapy workflow.

RESULTS

Model testing results confirmed the models were capable of producing VMAT plans within a single optimization that were overall improved upon or dosimetrically comparable to original clinical plans. Direct application of RapidPlan on iCBCT datasets produced satisfactory intact prostate and prostate bed plans with generally improved target volume coverage/conformality and rectal sparing relative to iCBCT Verify plans as indicated by DVH values, though bladder metrics were marginally increased on average. Average PQM values for iCBCT RapidPlans were significantly improved compared to iCBCT Verify plans. The average time required [in mm:ss] to generate adapted plans was 06:09 ± 02:06 (intact) and 07:12 ± 01:04 (bed).

CONCLUSION

This study demonstrated the feasibility of leveraging RapidPlan to expeditiously generate adapted VMAT intact prostate and prostate bed plans on iCBCT datasets. In general, adapted plans were dosimetrically improved relative to scheduled plans, emphasizing the practicality of the proposed approach.