Moving target irradiation with fast rescanning and gating in particle therapy

TLDR

Interplay between target motion and pencil‑beam scanning causes over‑ or under‑dosing in moving‑target irradiation. The study aimed to mitigate this effect by investigating rescanning with a gating technique. Simulation and experimental work using HIMAC’s fast scanning system tested a phase‑controlled rescanning method that matches each slice’s irradiation time to the gating duration. The method reduced dose discrepancies to less than 2 % and produced dose distributions close to the planned values, with only limited lateral and distal blurring observed in 3‑D experiments.

Abstract

Purpose: In moving target irradiation with pencil beam scanning, the interplay effect between the target motion and the scanned beam is a problem because this effect causes over or under dosage in the target volume. To overcome this, we have studied rescanning using a gating technique. Methods: A simulation and experimental study was carried out. In the experiment, we used the fast scanning system developed at the HIMAC to verify the validity of phase controlled rescanning method, in which the time for rescanning irradiation of each slice is matched to the gating duration. Results: Simulation and experimental results showed that controlling the scan speed to match the respiration cycle with rescans can deliver the blurred dose distribution. In the comparison between the static measurements and the moving measurements with the phase controlled rescanning method, the dose difference was less than 2% for pinpoint chambers in the target volume. Conclusions: The simulation and experimental results demonstrated that the phase controlled rescanning method makes it possible to deliver the dose distribution close to the expected one. As an experimental result for 3D irradiation, it was estimated that blurring by the probability density function was not only for a lateral distribution, but also for a distal distribution, even in the lateral rescanning.