Room: AAPM ePoster Library
A volumetric repainting technique has been proposed as one of the motion management techniques to mitigate the interplay in pencil beam scanning (PBS) proton therapy. The volumetric repainting implies repetitive scanning through the whole target volume. We have provided our technical experience on the clinical commissioning of a novel volumetric repainting technique in PBS proton therapy.
The commissioning was divided into three sections:(1) Beam dosimetry: including various types of maps to measure spot sizes, spot positions, and range. Specifically, the beam delivery includes irradiation from the deepest layer to the most proximal layer (“down” direction) as well as from the most proximal layer to the deepest layer (“up” direction). Range was measured using a multi-layer ionization chamber, whereas the spot sizes and positions were measured using 2D and 3D scintillation detectors. All measurements were performed in a movie mode (i.e.,without pausing beam after each layer) mimicking a real patient treatment delivery.(2) Treatment planning and delivery: included the creation of volumetric repainting plans (lung and liver) and delivery of them to a static 2D-array for gamma index analysis. (3) Tumor motion simulation: included a 6D robotic motion system and a phantom/detector simulating different magnitude of tumor motion. Treatment plans are generated using 2-4 volumetric repaintings and delivered to the phantom/detector to determine the optimal number of volumetric repaintings needed for a given magnitude of tumor motion.
On average, the layer switching time in “down” and “up” directions were 0.97s and 1.31s, respectively. The results from beam dosimetry and treatment planning/delivery tests were found to be within the TG-224 recommended tolerances for proton machine QA. Currently, a 6D robotic motion/phantom study is underway at our proton center.
Technical experience presented herein can potentially be used by clinical physicists for the commissioning of volumetric repainting in PBS proton therapy.