Randomized self-controlled study comparing open-face vs. closed immobilization masks in fractionated cranial radiotherapy.

PURPOSE: To compare patient discomfort and immobilisation performance of open-face and closed immobilization masks in cranial radiotherapy. MATERIAL AND METHODS: This was a single-center randomized self-controlled clinical trial. At CT simulation, an open-face and closed mask was made for each patient and treatment plans with identical dose prescription were generated for each mask. Patients were randomised to start treatment with an open-face or closed mask. Masks were switched halfway through the treatment course; every patient was their own control. Patients self-reported discomfort, anxiety and pain using the visual analogue scale (VAS). Inter- and intrafraction set-up variability was measured with planar kV imaging and a surface guided radiotherapy (SGRT) system for the open-face masks. RESULTS: 30 patients with primary or metastatic brain tumors were randomized - 29 completed radiotherapy to a median total dose of 54 Gy (range 30-60 Gy). Mean discomfort VAS score was significantly lower with open-face masks (0.5, standard deviation 1.0) vs. closed masks (3.3, standard deviation 2.9), P < 0.0001. Anxiety and pain VAS scores were significantly lower with open-face masks (P < 0.0001). Closed masks caused more discomfort in infraorbital (P < 0.001) and maxillary (P = 0.02) areas. Two patients and 27 patients preferred closed or open-face masks, respectively. Interfraction longitudinal shifts and roll and yaw rotations were significantly smaller and lateral shifts were significantly larger with closed masks in combination with the laser system (P < 0.05) compared to open masks in combination with a SGRT system. Intrafraction variability did not differ between the masks. CONCLUSIONS: Open-face masks are associated with decreased patient discomfort without compromising patient positioning and immobilisation accuracy.

Operating procedures, risk management and challenges during implementation of adaptive and non-adaptive MR-guided radiotherapy: 1-year single-center experience.

BACKGROUND: Main purpose was to describe procedures and identify challenges in the implementation process of adaptive and non-adaptive MR-guided radiotherapy (MRgRT), especially new risks in workflow due to the new technique. We herein report the single center experience for the implementation of (MRgRT) and present an overview on our treatment practice. METHODS: Descriptive statistics were used to summarize clinical and technical characteristics of treatment and patient characteristics including sites treated between April 2019 and end of March 2020 after ethical approval. A risk analysis was performed to identify risks of the online adaptive workflow. RESULTS: A summary of the processes on the MR-Linac including workflows, quality assurance and possible pitfalls is presented. 111 patients with 124 courses were treated during the first year of MR-guided radiotherapy. The most commonly treated site was the abdomen (42% of all treatment courses). 73% of the courses were daily online adapted and a high number of treatment courses (75%) were treated with stereotactic body irradiation. Only 4/382 fractions could not be treated due to a failing online adaptive quality assurance. In the risk analysis for errors, the two risks with the highest risk priority number were both in the contouring category, making it the most critical step in the workflow. CONCLUSION: Although challenging, establishment of MRgRT as a routinely used technique at our department was successful for all sites and daily o-ART was feasible from the first day on. However, ongoing research and reports will have to inform us on the optimal indications for MRgRT because careful patient selection is necessary as it continues to be a time-consuming treatment technique with restricted availability. After risk analysis, the most critical workflow category was the contouring process, which resembles the need of experienced staff and safety check paths.

Benefit of replanning in MR-guided online adaptive radiation therapy in the treatment of liver metastasis.

PURPOSE: To assess the effects of daily adaptive MR-guided replanning in stereotactic body radiation therapy (SBRT) of liver metastases based on a patient individual longitudinal dosimetric analysis. METHODS: Fifteen patients assigned to SBRT for oligometastatic liver metastases underwent daily MR-guided target localization and on-table treatment plan re-optimization. Gross tumor volume (GTV) and organs at risk (OARs) were adapted to the anatomy-of-the-day. A reoptimized plan (RP) and a rigidly shifted baseline plan (sBP) without re-optimization were generated for each fraction. After extraction of DVH parameters for GTV, planning target volume (PTV), and OARs (stomach, duodenum, bowel, liver, heart) plans were compared on a per-patient basis. RESULTS: Median pre-treatment GTV and PTV were 14.9 cc (interquartile range (IQR): 7.7-32.9) and 62.7 cc (IQR: 42.4-105.5) respectively. SBRT with RP improved PTV coverage (V100%) for 47/75 of the fractions and reduced doses to the most proximal OARs (D1cc, Dmean) in 33/75 fractions compared to sBP. RP significantly improved PTV coverage (V100%) for metastases within close proximity to an OAR by 4.0% (≤ 0.2 cm distance from the edge of the PTV to the edge of the OAR; n = 7; p = 0.01), but only by 0.2% for metastases farther away from OAR (> 2 cm distance; n = 7; p = 0.37). No acute grade 3 treatment-related toxicities were observed. CONCLUSIONS: MR-guided online replanning SBRT improved target coverage and OAR sparing for liver metastases with a distance from the edge of the PTV to the nearest luminal OAR < 2 cm. Only marginal improvements in target coverage were observed for target distant to critical OARs, indicating that these patients do not benefit from daily adaptive replanning.

First magnetic resonance imaging-guided cardiac radioablation of sustained ventricular tachycardia.

PURPOSE: To report the feasibility of magnetic resonance imaging-guided cardiac single fraction radioablation (MRgRA) in a patient with dilated cardiomyopathy and recurrent sustained ventricular tachycardia (VT) leading to electrical storms (ES). MATERIALS/METHODS: A workflow to perform Stereotactic Arrhythmia Radioablation (STAR) on a hybrid MR-Linac with real-time tracking and beam-gating was established. Challenges of the MRgRA approach included: (a) the safety of a non-MR compatible cardiac implantable electronic device (CIED) in the MR-Linac field, (b) artefacts caused by the CIED and (c) respiratory motion management with cine-tracking of the moving heart. The specific absorption rate and slew rate of the MR-Linac were within the specifications of a MR-conditional CIED. Phantom measurements showed CIED distortion artefacts of less than 1.5 mm. During MR simulation, tracking could be established on the upper liver to avoid interference with the moving heart and CIED extinction artefacts. Areas of anatomical scarring and critical substrate were identified using invasive three-dimensional electroanatomical mapping of the clinical VT during electrophysiological studies and cardiac MR imaging/computed tomography to build a volumetric target. RESULTS: A 71-year-old male patient with non-ischemic dilated cardiomyopathy and recurrent therapy-refractory sustained VT with repetitive implantable cardioverter-defibrillator (ICD) shocks was treated with a single fraction of 25 Gy @85% isodose, cine-tracking time was 46 min, beam-on time 24 min. 24 h post intervention the patient developed an aggravation of the clinical VT and prolonged ES. VT ceased following high-dose dexamethasone administration after 48 h. After this point, the patient remained without any episodes of sustained ventricular tachyarrhythmia requiring ICD interventions until the last follow-up at three months. CONCLUSION: Real-time tracking and beam-gating were successfully applied in this first MRgRA to treat sustained VT.