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The AlignRT Plus system is indicated for use to position and monitor patients relative to the prescribed treatment isocentre, and to withhold the beam automatically during radiation delivery. For cranial treatments, a manual head adjuster is included which can be used in concert with AlignRT Plus to provide fine corrections for pitch, roll and yaw rotations. AlignRT Plus is also used to track the patient's respiratory pattern for respiratory synchronized image acquisition therapy treatment. Patient contour data can be extracted and exported from the data acquired for the purpose of treatment planning. AlignRT Plus can be calibrated directly to the treatment beam isocentre and in turn assists in performing quality assurance on MV, kV imagers, room lasers and the treatment couch. AlignRT Plus is indicated for use during simulation, setup and stereotactic radiosurgery and precision radiotherapy for lesions, tumors and conditions anywhere in the body where radiation is indicated.

AlignRT Plus system is a combination of the predicate devices AlignRT (K052682) and GateCT-RT (K072171). It is a video-based three-dimensional (3D) surface imaging system, which is used to image the skin surface of a patient in 3D before and during radiotherapy treatment. The system consists of advanced software, a computer workstation, and one, two or three 3D camera units (each camera unit comprising a stereo pair of sensors to allow 3D surface reconstruction). The system is non-invasive, does not require the use of body markers and produces no ionizing irradiation during the imaging process.

Acceptance Criteria and Study for AlignRT Plus

The AlignRT Plus system is a video-based three-dimensional (3D) surface imaging system used to position and monitor patients during radiotherapy treatment. The following describes its acceptance criteria and the study demonstrating its performance.

1. Table of Acceptance Criteria and Reported Device Performance

Note: The document focuses on demonstrating substantial equivalence to predicate devices (AlignRT K052682 and GateCT-RT K072171) rather than presenting a detailed, independent clinical study with specific acceptance criteria outside of the technical specifications listed above. The performance metrics listed effectively serve as the acceptance criteria for technical performance.

2. Sample Size and Data Provenance

The provided document (510(k) Premarket Notification) does not explicitly state specific sample sizes used for a test set for the AlignRT Plus device itself.

Instead, it relies on demonstrating substantial equivalence to its predicate devices. The performance figures presented are derived from:

• Calibration phantom measurements: For positioning accuracy of the AlignRT Plus. The type and number of measurements are not specified.
• Respiratory tracking performance: For AlignRT Plus, again using measurements from imaged surface data. The number of breathing cycles (10 or more) is mentioned, but not the number of patients or measurement instances.
• Predicate device performance: The system accuracy for the predicate AlignRT (K052682) is cited, presumably from the studies conducted for its prior clearance.

Data Provenance: The document originates from Vision RT Ltd. in the United Kingdom. The data presented is likely derived from internal testing and validation activities characteristic of a premarket notification, rather than a large-scale, multi-center clinical trial. It is an internal retrospective analysis of technical performance.

3. Number of Experts and Qualifications for Ground Truth

The document does not detail the use of a panel of experts to establish a "ground truth" for a specific test set in the context of a reader study. The performance metrics (positioning accuracy, respiratory tracking RMS error) are objective technical measurements performed using phantoms or direct measurements from physical surfaces/breathing cycles. Therefore, expert consensus in the traditional sense for image interpretation is not directly applicable here.

4. Adjudication Method for the Test Set

Given that the "ground truth" is based on objective physical measurements (e.g., target registration errors from a phantom, RMS errors from surface displacement tracking), an adjudication method in the sense of reconciling divergent expert opinions is not applicable or described. The measurements are presumably taken directly and automatically by the system or calibrated instruments.

5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study

No MRMC comparative effectiveness study is presented or mentioned in this 510(k) premarket notification. The document focuses on the technical capabilities and safety of the device to demonstrate substantial equivalence to previously cleared predicate devices. It does not assess the improvement of human readers with AI assistance because the device is a patient positioning and monitoring system, not an AI-assisted diagnostic or treatment planning tool that directly involves human readers' interpretation of output in the same way an imaging AI might.

6. Standalone (Algorithm Only) Performance Study

Yes, the performance data provided largely represents standalone (algorithm only) performance. The metrics of positioning accuracy and respiratory tracking capability describe the intrinsic technical accuracy of the AlignRT Plus system in performing its designated functions (e.g., identifying target registration errors, tracking surface displacements) without direct human intervention in the measurement process itself. The "user" interaction described pertains to setup (e.g., selecting tracking points) and monitoring, but the reported accuracy figures are inherent to the system's measurements.

7. Type of Ground Truth Used

The ground truth for the reported performance metrics is based on objective physical measurements rather than expert consensus, pathology, or outcomes data:

• Target registration errors: Established using a physical calibration phantom with known, precise reference points.
• Surface displacements/respiratory tracking: Established by measuring the movement of the imaged surface against known or expected movements (e.g., during breathing cycles).

8. Sample Size for the Training Set

The document does not specify a sample size for a training set. As a medical device for patient positioning and monitoring, the AlignRT Plus utilizes algorithms for 3D surface reconstruction and tracking. While such algorithms undergo internal development and validation, the 510(k) summary does not typically disclose details of internal algorithm training data, particularly for devices that are not primarily AI/ML-driven in the diagnostic sense. The underlying principles are based on established optical and image processing techniques.

9. How Ground Truth for the Training Set Was Established

Given that a specific training set size is not provided, the method for establishing ground truth for any internal training or validation of the algorithms is not detailed in this public document. It is implicitly assumed to be based on engineering validation and testing using phantoms or controlled environments to ensure the accuracy of the 3D surface reconstruction and tracking algorithms.

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