Feasibility of patient-specific quality assurance (PSQA) for real-time robotic stereotactic body radiotherapy (SBRT) based on tumor motion traces.

PURPOSE: To design a patient specific quality assurance (PSQA) process for the CyberKnife Synchrony system and quantify its dosimetric accuracy using a motion platform driven by patient tumor traces with rotation. METHODS: The CyberKnife Synchrony system was evaluated using a motion platform (MODUSQA) and a SRS MapCHECK phantom. The platform was programed to move in the superior-inferior (SI) direction based on tumor traces. The detector array housed by the StereoPhan was placed on the platform. Extra rotational angles in pitch (head down, 4.0° ± 0.15° or 1.2° ± 0.1°) were added to the moving phantom to examine robot capability of angle correction during delivery. A total of 15 Synchrony patients were performed SBRT PSQA on the moving phantom. All the results were benchmarked by the PSQA results based on static phantom. RESULTS: For smaller pitch angles, the mean gamma passing rates were 99.75% ± 0.87%, 98.63% ± 2.05%, and 93.11% ± 5.52%, for 3%/1 mm, 2%/1 mm, and 1%/1 mm, respectively. Large discrepancy in the passing rates was observed for different pitch angles due to limited angle correction by the robot. For larger pitch angles, the corresponding mean passing rates were dropped to 93.00% ± 10.91%, 88.05% ± 14.93%, and 80.38% ± 17.40%. When comparing with the static phantom, no significant statistic difference was observed for smaller pitch angles (p = 0.1 for 3%/1 mm), whereas a larger statistic difference was observed for larger pitch angles (p < 0.02 for all criteria). All the gamma passing rates were improved, if applying shift and rotation correction. CONCLUSIONS: The significance of this work is that it is the first study to benchmark PSQA for the CyberKnife Synchrony system using realistically moving phantoms with rotation. With reasonable delivery time, we found it may be feasible to perform PSQA for Synchrony patients with a realistic breathing pattern.

Evaluation of a novel patient-specific quality assurance phantom for robotic single-isocentre, multiple-target stereotactic radiosurgery, and stereotactic radiotherapy.

OBJECTIVES: To evaluate patient-specific quality assurance (PSQA) of 3 targets in a single delivery using a novel film-based phantom. METHODS: The phantom was designed to rotate freely as a sphere and could measure 3 targets with film in a single delivery. After identifying the coordinates of 3 targets in the skull, the rotation angles about the equator and meridian were computed for optimal phantom setup, ensuring the film plane intersected the 3 targets. The plans were delivered on the CyberKnife system using fiducial tracking. The irradiated films were scanned and processed. All films were analysed using 3 gamma criteria. RESULTS: Fifteen CyberKnife test plans with 3 different modalities were delivered on the phantom. Both automatic and marker-based registration methods were applied when registering the irradiated film and dose plane. Gamma analysis was performed using a 3%/1 mm, 2%/1 mm, and 1%/1 mm criteria with a 10% threshold. For the automatic registration method, the passing rates were 98.2% ± 1.9%, 94.2% ± 3.7%, and 80.9% ± 6.3%, respectively. For the marker-based registration approach, the passing rates were 96.4% ± 2.7%, 91.7% ± 4.3%, and 78.4% ± 6.2%, respectively. CONCLUSIONS: A novel spherical phantom was evaluated for the CyberKnife system and achieved acceptable PSQA passing rates using TG218 recommendations. The phantom can measure true-composite dose and offers high-resolution results for PSQA, making it a valuable device for robotic radiosurgery. ADVANCES IN KNOWLEDGE: This is the first study on PSQA of 3 targets concurrently on the CyberKnife system.

Tumor Control Probability and Time-Dose-Response Modeling for Stereotactic Radiosurgery of Uveal Melanoma.

PURPOSE: Uveal melanoma (UM), although a rare malignancy, stands as the most prevalent intraocular malignancy in adults. Controversies persist regarding the dose dependency of local control (LC) through radiation therapy. This study sought to elucidate the significance of the prescription dose by employing time-dose-response models for patients with UM receiving photon-based stereotactic radiosurgery (SRS). METHODS AND MATERIALS: The analysis included patients with UM treated between 2005 and 2019. All patients underwent single-fraction SRS. Datapoints were separated into 3 dose groups, with Kaplan-Meier analysis performed on each group, from which time-dose-response models for LC were created at 2, 4, and 7 years after SRS using maximum-likelihood fitted logistic models. RESULTS: Outcomes from 594 patients with 594 UMs were used to create time-dose-response models. The prescribed doses and the number of patients were as follows: 17 to 19 Gy (24 patients), 20 Gy (122 patients), 21 Gy (442 patients), and 22 Gy (6 patients). Averaged over all patients and doses, LC rates at 2, 4, and 7 years were 94.4%, 88.2%, and 69.0%, respectively. Time-dose-response models for LC demonstrated a dose-dependent effect, showing 2-year LC rates of more than 90% with 20 Gy and 95% with 22 Gy. For 4 years and a LC of 90%, a dose of approximately 21 Gy was required. After 7 years, the 21 Gy prescription dose was predicted to maintain a LC above 70%, sharply declining to less than 60% LC with 19 Gy and less than 40% with 18 Gy. CONCLUSIONS: In contrast to prior findings, the time-dose-response models for UM undergoing photon-based SRS emphasize the critical role of the prescription dose in achieving lasting LC. The dose selection must be carefully balanced against toxicity risks, considering tumor geometry and individual patient characteristics to tailor treatments accordingly.