Proposed Topic (Most preferred): :
Research and Innovations (new projects / technology / innovations / service models)
Proposed Topic (Second preferred): :
HA Young Investigators Session (Projects to be presented by HA staff who had joined HA for 10 years or less)
Authors (including presenting author) :
Mak YT(1), Wong WC(1), Law ML(1), Ngai HY(1), Ngar YK(1)
Affiliation :
(1) Department of Clinical Oncology, Tuen Mun Hospital
Introduction :
4D Computed tomography (4D-CT) plays a crucial role in radiotherapy (RT) treatment planning for moving tumors induced by respiration. Images from different respiration phases are commonly used to delineate treatment target volume based on the concept of mid-ventilation or internal target volume. Delineation of tumors can be enhanced by fusing with Magnetic resonance imaging (MRI) datasets which are superior in differentiation of lesions among soft tissues. However, registration of the 4D-CT & MRI image dataset can still be challenging due to motion phase difference. Scan time of MRI would also be vital for the comfort of patients with immobilization devices for radiotherapy during image acquisition.
Objectives :
To develop a vendor-neutral approach to acquire respiration phase correlated MRI image dataset with short scan time for improving delineation of moving target and enhancing the patient comfort in RT setting.
Methodology :
The patient with RT immobilization devices undergoes two scan sequences in 8 minutes. Audio guidance is provided for regulation of the respiration. The first sequence is a 4-minute T1 b-TFE cine-MR coronal scan of the diaphragm region. The patient’s respiration rate is usually 20 per minute, therefore around 80 breathing cycles are included. The diaphragm displacement in cranial-caudal direction from the images are binned into 10 phases by an in-house program. 10 delays from the expiration phase are then calculated in terms of milliseconds. The second sequence is a 4-minute T2W 3D navigated TSE sequence accelerated with SENSE. With the navigator echo technique, the diaphragm position is monitored and when it reaches the maximal expiration level, data acquisition is triggered. By applying the calculated phase delay to the trigger, a set of respiratory-phased MR images can be acquired.
Result & Outcome :
We demonstrated an audio-guided navigator-based MRI approach in RT setting. Validation on phantom and clinical trial results are promising. 15 Hepatocellular Carcinoma (HCC) case studies were conducted. Breathing rates ranged from 18 to 20 rpm. 20 or 30% phase of the 4D-CT were selected for treatment planning. Calculated phase delays ranged from 900 to 1300ms. Rigid image registrations were performed and no deformable registration was needed. In future development, together with synthetic CT technology, 4D-CT can be replaced and RT planning images can be solely based on MR data hence reducing radiation dose to patients.
