SU‐FF‐I‐07: Respiratory Correlated CT: Acceptance and Clinical Introduction

Abstract

Purpose: Respiratory correlated CT (RC‐CT) has the potential to enable individual margins and prevent geometrical miss in radiotherapy for lung cancer patients. The objective of this study was to develop a procedure for acceptance and clinical introduction of RC‐CT. Method and Materials: RC‐CT was performed with a modified Siemens Sensation 10 and Biograph PET/CT with extremely low pitch (0.1) in combination with a respiratory signal obtained by a pressure sensor in a chest belt. Two phantoms were used for acceptance: Phantom 1: A ventilator (12 and 20bpm) and balloon, on which metal markers and the chest belt were positioned. This phantom was used to test the accuracy of the system. Phantom 2: A sphere moving 34mm(A‐P), 6mm(L‐R) and 34mm(Cr‐Ca) at 18bpm was used to evaluate distortion. Clinical introduction: In 16 NSCLC RT patients an RC‐CT was performed and tumor movement was measured. The volume within which the visible tumor moved(IGTV), was delineated and projected onto the regular CT/PET used for treatment planning. Results: Phantom 1: Correlation between reconstructed and true displacement of the markers with respiration was excellent (R=.992 p<.001 for the vector movement). The relation between true and reconstructed displacement was not significantly different from identity. Phantom 2: The distortion was minimal, in each of the ten respiration phases the sphere volume (65cm3) was accurately reconstructed within 4cm3. Patients: In all patients, RC‐CT could be successfully performed without coaching. The duration of the scan was always less than 90 seconds, with the whole procedure completed within 10 minutes. An RC‐CT delivered an estimated dose of 20cGy (CTDI). Mean and range of movement was 2.5±1.6,0–6mm(A‐P), 1.4±1.7,0–5mm(L‐R) and 4.4±4.5,0–15mm(Cr‐Ca). Conclusion: A procedure for acceptance and clinical introduction of RC‐CT has been developed. The results of the tested RC‐CT system were satisfactory and the system is now in clinical use.