The Itappachi Universal Motion Platform for Accurate Dose Measurement in Thoracoabdominal Radiotherapy

We developed the "Itappachi" universal motion platform for measuring radiation doses under simulated respiratory motion in radiation therapy. The interplay effect, resulting from respiratory motion, degrades dose delivery precision in advanced treatments such as volumetric modulated arc therapy. The Itappachi platform is designed for precise dose measurement in dynamic scenarios through its ability to simulate respiratory motion. The platform features a large surface (580 mm × 380 mm), capable of supporting weights up to 56.8 kg, and moves with an amplitude of ±25 mm. It requires no silicone oil for maintenance, and it is controlled via Wi-Fi using user-owned devices, thereby reducing costs. Its motion accuracy was confirmed, with a maximum displacement error of 0.12 mm. Using the platform, we conducted dose measurements with a Delta4 Phantom under static, moving without gated irradiation, and moving with gated irradiation conditions. Gamma index analysis revealed excellent agreement for static and dynamic gated conditions (99.4%), while significant dose degradation occurred in the non-gated dynamic condition (32.6%). The Itappachi platform provides a cost-effective and accurate solution for dose measurement under respiratory motion by which it supports improved quality assurance in radiation therapy.