Modelling Internal Hepatic Movement With an External Abdominal Marker

Modelling Internal Hepatic Movement With an External Abdominal Marker Block for Use With a Real Time Position Monitoring System for Respiratory Gating

This study tests the feasibility and reproducibility of patient-specific motion models. These will be used for quantification of safe margin reduction. Patient-specific motion models will be built by post-processing 4D MRI data with non-rigid registration. By comparing these models between visits, model reproducibility will be assessed, and the methodology refined.

The study will use a real time position management (RPM) system for respiratory gating. The RPM system senses the respiration motion of the patient by tracking a pair of reflective markers on a lightweight "marker block" constructed of a synthetic material. This block is placed on the patient's abdomen.

During Radiotherapy, the beam is only switched on at pre-determined phases of respiration. The appropriate phase of respiration is determined by the RPM system. This implies a reliable correlation of external block motion to internal hepatic movement. This correlation is not a simple one, and requires "modeling".

Inclusion Criteria:

• Histologically confirmed adenocarcinoma compatible with primary disease in the colon or rectum
• Aged 18 years or older
• Unequivocal contrast-enhanced CT and/or MRI evidence of malignant single or multiple metastases in the liver, metastases at other sites will not be an exclusion criterion
• WHO performance status 0-2 and life expectancy of at least 12 weeks
• Informed written consent

Exclusion Criteria:

• Pregnancy or breast feeding
• Evidence of ascites
• Patients unable for whatever reason to lie flat
• Patients unable to give fully informed consent
• Age< 18 years