ESTRO 2024 - Abstract Book

S4815

Physics - Quality assurance and auditing

ESTRO 2024

of a dedicated set of certified ionization chambers, including the PTW Bragg Peak Chamber 34070/34080 and the Roos 34001, along with a PTW MP3 water tank.

To ensure the accuracy in robot patient positioning, the system incorporated a number of comprehensive verification techniques. These included the use of fixed lasers in the accelerator nozzle and treatment room, as well as two orthogonal X-ray tubes operating at 150 kV, and the incorporation of two Varian Medical Systems PaxScan flat-panel detectors. Geometric evaluation prior to treatment planning was performed by monitoring the residual positioning error calculated by the 3D/3D and 2D/3D registration software using images of the anthropomorphic phantom used to generate the initial treatment plans.

Results:

Reproducibility of spot positioning was consistently accurate, with deviations well within ±1 mm in all tests performed. The width (sigma) of the Gaussian beam profile at the irradiation isocenter showed a clear energy dependence, ranging from a minimum of 2.8 mm to a maximum of 7.7 mm. During the commissioning phase, beam data including integrated depth dose curves (IDDs) and absolute dose values were carefully reviewed and evaluated against the recommendations of the IAEA TRS 398 protocol. This review confirmed the consistency of the commissioning data with the established guidelines. This data set was then integrated into the treatment planning system (TPS) according to the instructions provided by the TPS manufacturer, RaySearch Laboratories. The robot positioning showcased consistent reproducibility, maintaining deviations within the range of ±1 mm. Positioning accuracy was monitored as a 3-dimensional shift between the desired patient position defined by the treatment plan and the actual position measured by 2D/3D image registration. In order to assess the practical efficacy of the system, standard treatment plans were designed to cover a range of clinical scenarios, including head and neck, thoracic and abdominal treatments. These plans underwent a comprehensive dosimetric evaluation using the IBA MatriXX PT, which included extensive gamma analysis (3%, 3 mm). The results showed pass rates in excess of 95% for all clinical scenarios, confirming the system's ability to deliver accurate and effective treatment. In addition, the system's built-in dose monitoring system was tested to ensure its ability to generate critical interlocks in the event of specific failures. These failure scenarios included criteria such as a beam spot deviation greater than 2 mm, a single spot dose deviation of 10% or greater than 0.25 Gy, and a spot energy deviation greater than 0.5 MeV. The beam delivery interlocks performed as designed, serving as a fail-safe mechanism to ensure safe and precise delivery of radiation.

Conclusion:

We present the operation and commissioning results of an innovative single-room gantry-less system intensity modulated proton therapy (IMPT). This system includes a compact synchrotron and a flexible robotic patient positioning system that can be adjusted from near supine to upright positions. The commissioning results demonstrate high precision and consistency in both the primary proton beam delivery characteristics and the patient positioning system. This new proton therapy facility started patient treatments in March 2023. It was the first proton therapy treatment system in Israel and the entire Middle Eastern region.