A breathing thorax phantom with independently programmable 6D tumour motion for dosimetric measurements in radiation therapy

Abstract

Irradiation of moving targets using a scanned ion beam can cause clinically intolerable under- and overdosages within the target volume due to the interplay effect. Several motion mitigation techniques such as gating, beam tracking and rescanning are currently investigated to overcome this restriction. To enable detailed experimental studies of potential mitigation techniques a complex thorax phantom was developed. The phantom consists of an artificial thorax with ribs to introduce density changes. The contraction of the thorax can be controlled by a stepping motor. A robotic driven detector head positioned inside the thorax mimics e.g. a lung tumour. The detector head comprises 20 ionization chambers and 5 radiographic films for target dose measurements. The phantom's breathing as well as the 6D tumour motion (3D translation, 3D rotation) can be programmed independently and adjusted online. This flexibility allows studying the dosimetric effects of correlation mismatches between internal and external motions, irregular breathing, or baseline drifts to name a few. Commercial motion detection systems, e.g. VisionRT or Anzai belt, can be mounted as they would be mounted in a patient case. They are used to control the 4D treatment delivery and to generate data for 4D dose calculation. To evaluate the phantom's properties, measurements addressing reproducibility, stability, temporal behaviour and performance of dedicated breathing manoeuvres were performed. In addition, initial dosimetric tests for treatment with a scanned carbon beam are reported.

Feasibility Study on Cardiac Arrhythmia Ablation Using High-Energy Heavy Ion Beams

“…Dose was measured by pinpoint ionization chambers attached to an industrial robotic arm51. Static and dynamic QA was performed, with the arm being stationary or moving in the motion trajectory extracted from the cardiac 4DCT.…”

Upgrade and benchmarking of a 4D treatment planning system for scanned ion beam therapy

“…The absorbed dose was measured with an array of 24 pinpoint ionization chambers as reported by Karger et al 57 Three-dimensional sinusoidal motion of the ionization chamber array was facilitated using a robotic arm. 58 Peak-to-peak motion amplitudes of 20 mm in LR BEV and 10 mm in the remaining dimensions were chosen. Additionally, nongated static reference irradiations were performed.…”

Scanned Ion Beam Therapy of Moving Targets with Beam Tracking

“…At GSI a more complex geometry similar to a patient thorax is currently under development (Steidl et al 2011). However, more detailed assessment for a patient geometry has to be assured for clinical usage.…”