The value of magnetic resonance imaging in target volume delineation of base of tongue tumours – A study using flexible surface coils

Ahmed, Merina; Schmidt, Maria; Sohaib, Aslam; Kong, Christine; Burke, Kevin; Richardson, Cheryl; Usher, Marianne; Brennan, Sinead; Riddell, Angela; Davies, Mark; Newbold, Kate; Harrington, Kevin J.; Nutting, Christopher M.

doi:10.1016/j.radonc.2009.12.021

« Previous Next »Radiotherapy & Oncology
Volume 94, Issue 2 , Pages 161-167, February 2010

The value of magnetic resonance imaging in target volume delineation of base of tongue tumours – A study using flexible surface coils

Merina Ahmed
- Department of Radiotherapy, The Royal Marsden NHS Foundation Trust, London, UK
- Corresponding author. Address: Department of Radiotherapy, The Royal Marsden NHS Foundation Trust, Fulham Road, London SW3 6JJ, UK.
Maria Schmidt
- Cancer Research UK Clinical Magnetic Resonance Group, The Royal Marsden NHS Foundation Trust, Surrey, UK
Aslam Sohaib
- Department of Radiology, The Royal Marsden NHS Foundation Trust, London, UK
Christine Kong
- Department of Radiotherapy, The Royal Marsden NHS Foundation Trust, London, UK
Kevin Burke
- Department of Radiotherapy, The Royal Marsden NHS Foundation Trust, London, UK
Cheryl Richardson
- Cancer Research UK Clinical Magnetic Resonance Group, The Royal Marsden NHS Foundation Trust, Surrey, UK
Marianne Usher
- Cancer Research UK Clinical Magnetic Resonance Group, The Royal Marsden NHS Foundation Trust, Surrey, UK
Sinead Brennan
- Department of Radiotherapy, St. James’s Hospital, Dublin, Ireland
Angela Riddell
- Department of Radiology, The Royal Marsden NHS Foundation Trust, London, UK
Mark Davies
- Department of Radiotherapy, The Royal Marsden NHS Foundation Trust, London, UK
Kate Newbold
- Department of Radiotherapy, The Royal Marsden NHS Foundation Trust, London, UK
Kevin J. Harrington
- Department of Radiotherapy, The Royal Marsden NHS Foundation Trust, London, UK
- The Institute of Cancer Research, London, UK
Christopher M. Nutting
- Department of Radiotherapy, The Royal Marsden NHS Foundation Trust, London, UK
- The Institute of Cancer Research, London, UK

Received 19 October 2009; received in revised form 16 December 2009; accepted 20 December 2009. published online 25 January 2010.

Abstract

Introduction

Magnetic resonance imaging (MRI) provides superior diagnostic accuracy over computed tomography (CT) in oropharyngeal tumours. Precise delineation of the gross tumour volume (GTV) is mandatory in radiotherapy planning when a GTV boost is required. CT volume definition in this regard is poor. We studied the feasibility of using flexible surface (flex-L) coils to obtain MR images for MR–CT fusion to assess the benefit of MRI over CT alone in planning base of tongue tumours.

Methods

Eight patients underwent CT and MRI radiotherapy planning scans with an immobilisation device. Distortion-corrected T1-weighted post-contrast MR scans were fused to contrast-enhanced planning CT scans. GTV, clinical target and planning target volumes (CTV, PTV) and organs at risk (OAR) were delineated on CT, then on MRI with blinding to the CT images. The volumetric and spatial differences between MRI and CT volumes for GTV, CTV, PTV and OAR were compared. MR image distortions due to field inhomogeneity and non-linear gradients were corrected and the need for such correction was evaluated.

Results

The mean primary GTV was larger on MRI (22.2 vs. 9.5cm³, p=0.05) than CT. The mean primary and nodal GTV (i.e. BOT and macroscopic nodes) was significantly larger on MRI (27.2 vs. 14.4cm³, p=0.05). The volume overlap index (VOI) between MRI and CT for the primary was 0.34 suggesting that MRI depicts parts of the primary tumour not detected by CT. There was no significant difference in volume delineation between MR and CT for CTV, PTV, nodal CTV and nodal PTV. MRI volumes for brainstem and spinal cord were significantly smaller due to improved organ definition (p=0.002). Susceptibility and gradient-related distortions were not found to be clinically significant.

Conclusion

MRI improves the definition of tongue base tumours and neurological structures. The use of MRI is recommended for GTV dose-escalation techniques to provide precise depiction of GTV and improved sparing of spinal cord and brainstem.

Keywords: MRI, Volume delineation, Oropharynx