ESTRO 2024 - Abstract Book

S4392

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

radiographs were acquired using a pencil beam scanning system at the Marburg Ion Therapy Center, Germany. A simplified representation of a lung tumour was achieved by having a 3 cm diameter sphere, in air, sandwiched between 11.5 cm of water equivalent material (7.5 cm in front and 4cm behind). The sphere was mounted on a linear motion table which could be programmed to undergo a known motion. Using this simplified lung model, 6 cm x 6 cm frames of were acquired with a spot spacing of 5 mm and a frame rate of 1.0 s for carbon ions and 0.85 s protons. Each frame was reconstructed by summing the light output detected by the distal camera, from each of the constituent pencil-beams, and the sphere position determined from the center of mass of its projection. The accuracy of motion tracking, defined as the mean absolute error between the detected sphere positions and its expected position at that time according to the table motion, was calculated over the whole acquisition.

Results:

Images demonstrating motion were successfully acquired for both proton and carbon ion radiographs (Figure 1). Carbon radiographs show significantly better image quality than their proton counterparts due to reduced scattering in the phantom and detector.