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The RefleXion Medical Radiotherapy System is indicated for treatment planning and precise delivery of image-guided radiation therapy, stereotactic radiotherapy, or stereotactic radiosurgery for tumors or other targeted tissues anywhere in the body when radiation treatment is indicated, while minimizing the delivery of radiation to vital healthy tissue. The megavoltage X-ray radiation is delivered in a rotational, modulated, image-guided format in accordance with the physician approved plan.

The RefleXion Medical Radiotherapy System (RMRS), a hybrid imaging-therapy system, is capable of delivering intensity-modulated radiation therapy (IMRT), stereotactic body radiation therapy (SBRT), stereotactic radiotherapy (SRT) and stereotactic radiosurgery (SRS) utilizing an on-board kilovoltage CT (kVCT) system for patient localization and field sizes based on jaws which are 40 cm wide, with slice width choices of 1.0 cm and 2.0 cm to optimize patient treatment. It is also equipped with a binary multileaf collimator (MLC) used to create intensity modulated radiation fields at a source-axis distance of 85 cm. It can achieve a nominal dose rate of 850 cGy/min.

The RMRS consists of the following clinical subsystems: 6 MV photon radiotherapy delivery, Kilovoltage (KV) X-ray CT imaging, MV X-ray detection, and treatment planning. The LINAC along with the fixed primary collimator, adjustable collimators, and multileaf collimator (MLC) mount in the therapy plane. The kVCT imaging plane is separate from the therapy plane and provides images used to localize the patient prior to treatment. Additionally, the system is designed architecturally to include PET imaging components for future product enhancements. Although the PET subsystem hardware is present in the system, its functionality is currently disabled.

Here's an analysis of the acceptance criteria and study information provided in the document:

1. Acceptance Criteria and Reported Device Performance

Notes: The document states that "Results of bench testing showed conformance to applicable requirements and specifications" for all listed performance tests. While specific numerical results are provided for high and low contrast resolution, they are presented as comparisons to the predicate device rather than explicit acceptance criteria and direct performance measurements against those criteria. However, the implicit indication is that these improved or comparable values meet expectations.

2. Sample Size Used for the Test Set and Data Provenance

The document states, "No animal studies or clinical tests have been included with this pre-market submission." This indicates that the testing was primarily bench testing and in-vitro verification and validation. Therefore, the concept of a "test set" with "data provenance" in the clinical sense (e.g., patient data from a specific country, retrospective/prospective) is not applicable here.

3. Number of Experts Used to Establish the Ground Truth for the Test Set and Qualifications of Those Experts

Not applicable. As per point 2, no clinical test set was used that would require expert-established ground truth. The "ground truth" for the performance tests would be established through a combination of:

• Physical phantoms and measurement devices: For tests like dosimetric accuracy, isocenter coincidence, and geometric accuracy.
• Standards and specifications: The acceptance criteria themselves are drawn from industry standards and internal design specifications.

4. Adjudication Method for the Test Set

Not applicable, as no clinical test set requiring expert adjudication was used.

5. If a Multi Reader Multi Case (MRMC) Comparative Effectiveness Study was Done, If so, what was the effect size of how much human readers improve with AI vs without AI assistance

Not applicable. The RefleXion Medical Radiotherapy System is a radiation treatment and imaging system, not an AI-assisted diagnostic or interpretation tool for human readers. There is no mention of such a human reader study.

6. If a Standalone (i.e. algorithm only without human-in-the loop performance) was Done

The performance data presented in the table are for the standalone device performance (e.g., mechanical accuracy, dosimetric accuracy, imaging performance). The device's treatment planning software is part of the system, and its accuracy is tested (e.g., "Treatment Planning System Dose accuracy tests"), indicating a standalone assessment of the algorithm's output. These results are implied to be "conforming to applicable requirements and specifications."

7. The Type of Ground Truth Used

The ground truth for the verification and validation tests was established through:

• Physical measurements and industry standards: For mechanical, dosimetric, and imaging performance tests (e.g., phantoms, dosimeters, rulers, calibrated test equipment against known values).
• Design specifications and requirements: The device's performance was measured against its predefined technical specifications and relevant international standards (e.g., IEC standards).

8. The Sample Size for the Training Set

Not applicable. The document describes a medical device (a linear accelerator and its associated systems) and its performance, not a machine learning or AI model that requires a "training set" in the context of data-driven algorithm development. While the system undoubtedly has complex software, the document focuses on its overall and component performance validation rather than the training of a predictive model.

9. How the Ground Truth for the Training Set was Established

Not applicable, as there is no "training set" discussed in this submission.

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