An assessment of set up position for MRI scanning for the purposes of rectal cancer radiotherapy treatment planning.

INTRODUCTION: A magnetic resonance (MR) scanner for radiotherapy treatment simulation was commissioned in our department in June 2013. Practical set up and MR image quality trade-offs using a variety of patient positions and immobilisation devices routinely used in the treatment planning of rectal cancer patients were considered. The study also aimed to investigate the MR compatibility of the device materials with a focus on temperature changes during routine clinical examinations.

METHODS: Ten volunteers were scanned: (1) Prone on a Civco Contoura Bellyboard (BBB), (2) Prone on a Civco MR Series Bellyboard (WBB), (3) Prone with no bellyboard and (4) Supine. All scans were performed with a T2 weighted (T2 -w) turbo spin echo (TSE) sequence. Images were scored by five assessors for: (1) ease of identifying specific organs, (2) overall image quality and (3) signal to noise ratio (SNR). Temperature changes were measured for each volunteer in each position.

RESULTS: Both expert scores and SNR analysis demonstrated that images obtained in the supine position allowed for easier and clearer delineation of the organs. Image factors such as artefacts and noise, along with the overall image quality, also performed better in the supine position. The carbon fibre bellyboard did not demonstrate significant heating during scanning with the T2 -w TSE transverse sequence.

CONCLUSIONS: A supine position was determined to be superior to the other positions in a majority of comparisons. The volunteers did not experience any increased temperature changes during scanning on the bellyboard in comparison to the other positions.