PURPOSE:We conducted a multicenter study on single-isocenter multitarget stereotactic radiosurgery to dosimetrically assess end-to-end test results and identify approaches and techniques influencing spatial accuracy and treatment plan quality. METHODS AND MATERIALS:An anthropomorphic head phantom with radiochromic film and polymer gel inserts was used with a reference structure set of 5 brain metastases. End-to-end tests were performed on-site at 23 centers in Germany, Austria, and Switzerland, each following its own single-isocenter multitarget stereotactic radiosurgery protocol. Spatial accuracy was quantified by comparing planned and measured prescription isodose-volume centroids. Plan quality was assessed from treatment planning system calculations using the Paddick gradient index (GI) and Paddick conformity index. Statistical analyses, including a generalized linear model, correlated results with protocol parameters to identify favorable systems and techniques. RESULTS:The mean spatial offset between measured and calculated prescription isodose centroids across all centers and targets was 0.9 ± 0.4(1σ) mm. Offsets above 1 mm were observed in 33% of centers. Better imaging-to-radiation isocenter consistency (ICC) yielded significantly higher accuracy (P = .002): dICC<median = 0.6 ± 0.2 mm versus 1.1 ± 0.3 mm. Mean GI was 6.7 ± 3.3. Automated planning (AP) tools achieved significantly lower GI (4.9 ± 0.7) than conventional planning (8.1 ± 3.8, P = .015). Mean Paddick conformity index was 0.75 ± 0.17, with AP significantly improving conformity (0.83 ± 0.07 vs 0.68 ± 0.19; P = .028) and reducing variability in both indices. Target-to-isocenter distance had no significant influence on spatial accuracy, GI, or Paddick conformity index. CONCLUSIONS:Spatial accuracy in a static phantom was primarily determined by ICC and less by specific delivery infrastructure or techniques, emphasizing the importance of a precise imaging isocenter calibration. AP tools significantly improved and standardized treatment plan quality across centers.

Mandibular reconstruction with fibula free flaps commonly requires fixation using titanium osteosynthesis plates. In patients receiving adjuvant radiotherapy, scatter radiation effects from metallic hardware may alter dose distribution and affect biological responses, but systematic evidence remains limited. This experimental study examined the influence of plate geometry on scatter radiation and cell proliferation. A three-dimensional printed mandibular phantom, generated from patient CT data and combined with a water phantom, was used to simulate clinical irradiation conditions. Irradiation was performed with an Ethos linear accelerator, and dose modifications in the vicinity of different plate designs were analyzed. Human mesenchymal stromal cells (hMSC) and human umbilical vein endothelial cells (HUVEC) were irradiated under identical conditions, and proliferation was assessed using MTS assays. Distinct dose increases were detected anterior to the plates, with dose reductions in the shadowing region, depending on plate diameter and geometry. These physical changes correlated with significant differences in hMSC and HUVEC proliferation. The results indicate that osteosynthesis plate design affects both dosimetric distribution and cellular responses during radiotherapy. These findings suggest that reduced metal volume and specific plate geometries may contribute to lower local radiation perturbations and should be considered in reconstructive planning for patients undergoing adjuvant radiotherapy.

Conventional image-guided radiotherapy (IGRT) typically relies on a computed tomography (CT)-based treatment planning process (planning CT, pCT) performed prior to the start of treatment. During this process, a patient-specific treatment plan is generated, which is then delivered to the patient with a linear accelerator on a daily basis, usually with image guidance to compensate for variations in patient setup. However, daily interfractional anatomical variations in target position, shape, and volume, as well as in surrounding organs at risk (OARs), can only be addressed indirectly by adding safety margins, resulting in larger irradiated volumes and potentially increased toxicity. Online adaptive radiotherapy (oART) is a promising and innovative technique to reduce such margins and, consequently, treatment-related toxicity. It uses daily imaging to generate a “plan of the day” that is aligned with the current patient anatomy, often supported by artificial intelligence (AI), while the patient remains on the treatment couch. Through daily image-guided re-optimization of the radiation treatment (RT) plan on the anatomy of the day, target coverage may also be improved. This approach is particularly attractive in the pelvic region, where high interfractional anatomical variability, for example due to peristalsis or changes in bladder and rectal filling, is frequently observed. This prospective registry-based cohort study will include patients with pelvic or thoracic tumors with an indication for RT treated with IGRT or oART using the Varian Ethos™ system. The primary endpoint is defined as a 10

IntroductionDaily anatomical variations in prostate cancer radiotherapy, particularly due to pelvic organ motion and filling, can compromise target coverage and increase exposure to organs at risk (OARs). Conventional image-guided radiotherapy (IGRT) uses fixed safety margins and daily couch corrections to account for these variations, potentially leading to overtreatment of healthy tissue or insufficient tumor coverage. Online adaptive radiotherapy (oART), based on cone-beam computed tomography (CBCT), enables daily plan adaptation to the patient's anatomy, offering improved precision, enhanced target coverage, and better OAR sparing. This retrospective study compares oART to conventional IGRT in prostate cancer treatment.MethodsA total of 153 treatment fractions from six consecutive prostate cancer patients treated with oART on a Varian Ethos system were analyzed. For each fraction, three plans were evaluated: the scheduled plan (initial plan recalculated on daily CBCT), the adapted plan (reoptimized based on daily anatomy), and the verification plan (applied dose recalculated on a post-adaptation CBCT). Dose-volume metrics for target volumes and OARs were assessed, and clinical acceptability was evaluated. Interfractional prostate volume changes and treatment times were examined.ResultsCTV D98% improved significantly with adaptation (median 97.85% to 98.55%; p < 0.01) and further increased in the verification plan (98.8%; p < 0.01), alongside reduced interquartile ranges. PTV D98% rose from 90.1% to 97.1% with adaptation and to 96.9% after verification (p < 0.01). Bowel and bladder doses showed dosimetrical advantage. Clinically acceptable plans increased from 24.8% (scheduled) to 98% (adapted) and 85.6% (verification). Scheduled plans were not used clinically. Median prostate volume remained stable despite inter-individual variation. oART required about twice the treatment time of IGRT.ConclusionAlthough more time-consuming, oART improved target dose coverage and optimized OAR sparing, while simultaneously reducing dose variability for both the target and some OARs compared to IGRT. The plan acceptability improved significantly.

Bladder cancer radiotherapy presents unique challenges due to the dynamic anatomy of the bladder and the surrounding organs. Conventional image-guided radiotherapy (IGRT) relies on fixed treatment margins and daily couch corrections, which can result in suboptimal dose delivery. Cone Beam Computed Tomography (CBCT)-based online adaptive radiotherapy (oART) allows daily re-optimization of treatment plans, potentially improving target dose coverage while minimizing exposure to organs at risk (OAR). This study compares oART with IGRT in bladder cancer patients. 160 oART fractions delivered using the Ethos system (Varian Medical Systems, Palo Alto, CA, USA) were analyzed and compared to conventional IGRT. For each adaptive fraction (fx), three plans were evaluated: the scheduled plan (initial plan recalculated based on daily CBCT), the adapted plan (re-optimized to daily anatomy), and the verification plan (dose distribution recalculated on the verification CBCT - vCBCT). Geometric variations, dose-volume parameters and treatment times were analyzed. Clinical plan acceptability was assessed using predefined dose-volume parameters. Dose coverage on the target’s surface was analyzed using a novel method and visualized via Mercator projections. Despite drinking guidelines, bladder volumes varied significantly day-to-day. Dose coverage of the clinical target volume (CTV) improved significantly with adaptation (median D98

BACKGROUND:Stereotactic radiosurgery (SRS) is an emerging alternative to whole-brain radiotherapy (WBRT) for treating multiple brain metastases (BM), reducing toxicity, and improving tumor control. The CYBER-SPACE trial compared SRS based on either SPACE or MPRAGE MRI sequence for avoiding or delaying WBRT in patients with 1-10 BM. METHODS:Patients with 1-10 untreated BM were randomized 1:1 to receive SRS of all lesions based on either SPACE or MPRAGE MRI sequences. If subsequently new BM occurred, SRS was repeated. WBRT was indicated upon occurrence of >10 new BM, leptomeningeal disease, or exhausted SRS-radiotolerance. The primary outcome was freedom from WBRT indication (WBRTi). Secondary outcomes included overall survival (OS), safety, and quality of life. RESULTS:A total of 202 patients were randomized; SPACE n = 99, MPRAGE n = 103. Twelve-month WBRTi-free survival was 77.1% (95% CI: 69.5%-83.1%) overall, 78.5% (95% CI: 66.7%-86.5%) for SPACE, and 76.0% (95% CI: 65.2%-83.9%) for MPRAGE (hazard ratio [HR] = 0.84, 95% CI: 0.43-1.63, P = .590). Patients with 5-10 BM had shorter WBRTi-free survival (HR = 3.13, 95% CI: 1.53-6.40, P = .002). Median OS was 13.1 months overall, 10.5 months for SPACE, and 15.2 months for MPRAGE (HR = 1.10, 95% CI: 0.78-1.56, P = .585). Neurologic death rate was 10.1%. Predictors for longer OS included Karnofsky Performance Status >80% (HR = 0.51, 95% CI: 0.33-0.77, P = .002) and concurrent immunotherapy (HR = 0.34, 95% CI: 0.23-0.52, P < .001). CONCLUSIONS:The more sensitive SPACE sequence did not improve outcomes over MPRAGE. SRS with thorough monitoring and immediate re-treatment for new lesions decreases the need for WBRT and achieves low neurologic death rates. SRS should be considered a favorable alternative to WBRT for patients with 1-10 BM.

BACKGROUND:Postoperative radiotherapy improves local control after brain metastasis (BM) resection. Whole-brain radiotherapy (WBRT) reduces recurrence risk but impairs neurocognition. Hypofractionated stereotactic radiotherapy of the cavity (HFSRT) may offer equivalent tumor control with reduced toxicity. ESTRON is the first randomized trial comparing post-operative HFSRT and WBRT. METHODS:This single-center phase 2 trial randomized 56 patients with resected BM to receive HFSRT (35 Gy in 7 fractions) or WBRT (30 Gy in 10 fractions). Patients could have ≤ 10 additional unresected BMs. The primary endpoint was intracranial progression-free survival (ic-PFS). Secondary endpoints included local control (LC), overall survival (OS), leptomeningeal disease (LMD), and toxicity. RESULTS:Fifty-four patients were evaluable (n = 27 per arm). At 24.7 months median follow-up, 12-month ic-PFS was 44.4% (HFSRT) versus 59.3% (WBRT) (HR 1.72, P = .080). Median ic-PFS was 4.7 versus 15.0 months. LC at 24 months was 94.1% (HFSRT) versus 85.4% (WBRT) (HR 0.41, P = .433). One-year OS was 63.0% (HFSRT) versus 77.8% (WBRT), with no significant difference in median OS (17.8 vs 27.0 months; HR 1.09, P = .336). One-year risk of LMD was 27.0% (HFSRT, predominantly outside the irradiated field) versus 8.7% (WBRT) (log-rank P = .03). Treatment-related adverse events were more frequent with WBRT (115 vs 54 events), including 19% versus 11% grade 3 events, and poorer neurocognitive performance. CONCLUSIONS:Survival was similar for HFSRT and WBRT, while WBRT trended toward better ic-PFS. HFSRT showed substantially lower toxicity and better neurocognitive preservation, however, a higher risk of LMD. Risks and benefits should be weighed individually when determining post-operative treatment for BM.

Single-isocenter multitarget stereotactic radiosurgery (SIMT SRS) offers enhanced clinical efficiency for treating multiple brain metastases. However, it introduces additional uncertainties, such as off-center dose and beam profile inaccuracies, as well as quality assurance (QA) challenges, complicating its implementation. This study aims to evaluate different SIMT SRS approaches. We collected and analyzed SIMT SRS protocol and infrastructure parameters from 23 radiotherapy centers across Germany, Austria, and Switzerland, encompassing immobilization systems, computed tomography (CT) protocols, linear accelerators, treatment planning systems, beam configurations, imaging techniques, and QA practices. Consensus, deviations, and compliance with current guidelines were assessed. Subsequent studies will include on-site measurements, evaluation of treatment plan quality and delivery accuracy, and correlation of these findings with the analyzed protocols to identify potential links between protocol parameters and clinical outcomes. There is consensus (at least 80

The internal organ at risk volume (IRV) concept might improve toxicity profiles in stereotactic body radiation therapy (SBRT) for non-small cell lung cancer (NSCLC). We studied (1) clinical aspects in central vs. peripheral tumors, (2) the IRV concept in central tumors, (3) organ motion, and (4) associated normal tissue complication probabilities (NTCPs). We analyzed patients who received SBRT for NSCLC (clinical aspects, n = 78; motion management, n = 35). We found lower biologically effective doses, larger planning target volume sizes, higher lung doses, and worse locoregional control for central vs. peripheral tumors. Organ motion was greater in males and tall patients (bronchial tree), whereas volume changes were lower in patients with a high body mass index (BMI) (esophagus). Applying the IRV concept (retrospectively, without new optimization), we found an absolute increase of >10% in NTCPs for the bronchial tree in three patients. This study emphasizes the need to optimize methods to balance dose escalation with toxicities in central tumors. There is evidence that organ motion/volume changes could be more pronounced in males and tall patients, and less pronounced in patients with higher BMI. Since recent studies have made efforts to further subclassify central tumors to refine treatment, the IRV concept should be considered for optimal risk assessment.

Background Conventional Radiotherapy (Image Guided Radiotherapy, IGRT) requires a computed tomography (CT)-based treatment planning (planning CT, pCT) process a priori. During this process, a treatment plan is calculated, which then is applied to the patient with a linear accelerator on a daily basis, possibly using image guidance to account for variability in patient position. However, daily changes of the anatomy of targets and organs at risk (OARs) can only be addressed by applying additional safety margins, resulting in larger irradiated volumes and possibly higher toxicity. A promising and innovative technique for margin and in consequence toxicity reduction is online Adaptive Radiotherapy (oART) using daily imaging to create a “plan of the day” aligned to the actual anatomy by means of artificial intelligence (AI) and with the patient on the treatment couch. Through daily image-guided re-optimization of the radiation treatment (RT) plan, the target coverage may also be improved. This approach is especially promising in the pelvic region due to the high anatomic variability, e.g. caused by peristalsis or volume changes of bladder and rectum. Methods This prospective registry-based trial will include patients with pelvic or thoracic tumors with an indication for RT treated with IGRT or oART using the Varian Ethos™ system. The primary endpoint is defined as a 10% reduction in the rate of acute RT related toxicity (≥ Common Terminology Criteria for Adverse Events (CTCAE) II°, v5.0) using oART. Secondary endpoints encompass clinical outcomes including late toxicities, tumor control rates, and patient-reported outcomes, as well as technical factors such as target volume, coverage, dose to OARs and anatomical variability score. While the trial compares IGRT versus oART for primary and secondary clinical endpoints, it also evaluates the real oART scenario against two hypothetical control scenarios for technical endpoints. Discussion The introduction of oART promises a reduction in toxicities and improved target volume coverage, potentially resulting in enhanced tumor control rates. It is poised to be a pioneering technology in the field of radiation oncology. Given the absence of a direct comparison between IGRT and oART thus far, the PRoART trial aims to address this gap. Trial registration Clinicaltrials.gov, NCT06185062. Registered 12/14/2023. Last update 02/06/2024.

Accurate Magnetic Resonance Imaging (MRI) simulation is fundamental for high-precision stereotactic radiosurgery and fractionated stereotactic radiotherapy, collectively referred to as stereotactic radiotherapy (SRT), to deliver doses of high biological effectiveness to well-defined cranial targets. Multiple MRI hardware related factors as well as scanner configuration and sequence protocol parameters can affect the imaging accuracy and need to be optimized for the special purpose of radiotherapy treatment planning. MRI simulation for SRT is possible for different organizational environments including patient referral for imaging as well as dedicated MRI simulation in the radiotherapy department but require radiotherapy-optimized MRI protocols and defined quality standards to ensure geometrically accurate images that form an impeccable foundation for treatment planning. For this guideline, an interdisciplinary panel including experts from the working group for radiosurgery and stereotactic radiotherapy of the German Society for Radiation Oncology (DEGRO), the working group for physics and technology in stereotactic radiotherapy of the German Society for Medical Physics (DGMP), the German Society of Neurosurgery (DGNC), the German Society of Neuroradiology (DGNR) and the German Chapter of the International Society for Magnetic Resonance in Medicine (DS-ISMRM) have defined minimum MRI quality requirements as well as advanced MRI simulation options for cranial SRT.

BackgroundThe landscape of radiation oncology has evolved rapidly in recent years, driven by advancements in technology and increasing demands for quality control and patient care. To meet these challenges, structured and effective teaching methods are essential during residency training. Various organizations, such as ESTRO and DEGRO-Academy, have proposed curricula to standardize radiation oncology training. To address this issue and make it accessible to a broad audience, we established an online-based webinar series supervised by the German Society for Radiation Oncology (DEGRO) and the young DEGRO (yDEGRO) working group of the DEGRO. Starting in January 2021, selected lecturers taught curricular content monthly as preparation for the board exam in radiation oncology.MethodsBetween 01/2021 and 12/2022 we evaluated 24 courses using a standardized questionnaire with 21 items (recording epidemiological characteristics of the participants, didactic and content quality). A Likert scale (range: 1-4) was used in combination with binary and open questions.ResultsA total of 4200 participants enrolled in the educational courses. Out of these, 934 individuals filled out the feedback form (response rate: 22.2%). 36% of all participants were residents in radiation oncology, 35% specialists, 21% medical technologists for radiology (MTR) and 8% were medical physics experts (MPE)). Overall, participants rated the lectures as excellent (mean rating 2021: 1.33 versus 2022: 1.25) and the curriculum surpassed the offered at each training site for 70% of participants. Case-based learning emerged as a highly favored approach.DiscussionDigital teaching and learning have revolutionized education, particularly in the wake of the COVID-19 pandemic, leading to the adoption of innovative teaching methods in radiation oncology, including e-learning and telehealth. These digital formats offer flexibility and effectiveness in knowledge transfer, with the potential to enhance clinical care quality. Through participant evaluations and curriculum coverage analysis, we assess the webinar's impact on trainee physicians in Germany and beyond. Results indicate high participant satisfaction, with positive feedback on course content and didactic quality. The webinars cover a wide range of the curriculum for the German board exam in radiation oncology, demonstrating their potential to supplement traditional training methods. Feedback highlights areas for improvement, such as increased focus on practical relevance and interdisciplinary topics. Overall, the DEGRO webinar represents a valuable addition to radiation oncology education, offering standardized, high-quality teaching accessible to a diverse audience of physician, radiation biologists, medical technologists for radiology and medical physics experts.

Purpose/Objective The proximity or overlap of PTV and OAR poses a major challenge in SBRT of pancreatic cancer (PACA). This international treatment planning benchmark study investigates whether Simultaneously Integrated Boost (SIB) and Protection (SIP) concepts in PACA SBRT can lead to improved and harmonized plan quality. Materials/Methods A multiparametric specification of desired target doses (GTVD50%, GTVD99%, PTVD95%, PTV0.5cc) with two prescription doses of GTVD50%=5×9.2Gy (46Gy) and GTVD50%=8×8.25Gy (66Gy) and OAR limits were distributed with planning CT and contours from 3 PACA patients. In phase 1, plans were ranked using a scoring system for comparison of trade-offs between GTV/PTV and OAR. In phase 2, re-planning was performed for the most challenging case and prescription with dedicated SIB and SIP contours provided for optimization after group discussion. Results For all 3 cases and both phases combined, 292 plans were generated from 42 institutions in 5 countries using commonly available treatment planning systems. The GTVD50% prescription was performed by only 76% and 74% of planners within 2% for 5 and 8 fractions, respectively. The GTVD99% goal was mostly reached, while the balance between OAR and target dose showed initial SIB/SIP-like optimization strategies in about 50% of plans. For plan ranking, 149 and 217 score penalties were given for 5 and 8 fractions, pointing to improvement possibilities. For phase 2, the GTVD50% prescription was performed by 95% of planners within 2% and GTVD99% as well as OAR doses were better harmonized with notable less score penalties. Fourteen of 19 planners improved their plan rank, 9 of them by at least 2 ranks. Conclusion Dedicated SIB/SIP concepts in combination with multiparametric prescriptions and constraints can lead to overall harmonized and high treatment plan quality for PACA SBRT. Standardized SIB/SIP treatment planning in multicenter clinical trials appears feasible after group consensus and training.

Purpose Modern digital teaching formats have become increasingly important in recent years, in part due to the COVID-19 pandemic. In January 2021, an online-based webinar series was established by the German Society for Radiation Oncology (DEGRO) and the young DEGRO (yDEGRO) working group. In the monthly 120-minute courses, selected lecturers teach curricular content as preparation for the board certification exam for radiation oncology. Methods The evaluation of the 24 courses between 01.2021 and 12.2022 was performed using a standardized questionnaire with 21 items (recording epidemiological characteristics of the participants, didactic quality, content quality). A Likert scale (1–4) was used in combination with binary and open-ended questions. Results A combined total of 4200 individuals (1952 in 2021 and 2248 in 2022) registered for the courses, and out of those, 934 participants (455 in 2021 and 479 in 2022) later provided evaluations for the respective courses (36% residents, 35% specialists, 21% medical technicians for radiology [MTR], 8% medical physics experts [MPE]). After 2 years, 74% of the DEGRO Academy curriculum topics were covered by the monthly webinars. The overall rating by participants was positive (mean 2021: 1.33 and 2022: 1.25) and exceeded the curriculum offered at each site for 70% of participants. Case-based learning was identified as a particularly well-rated method. Conclusion The DEGRO webinar expands the digital teaching opportunities in radiation oncology. The consistently high number of participants confirms the need for high-quality teaching and underlines the advantages of e‑learning methods. Optimization opportunities were identified through reevaluation of feedback from course participants. In its design as a teaching format for a multiprofessional audience, the webinar series could be used as a practice model of online teaching for other disciplines.