International Journal of Radiation Oncology*Biology*Physics
Physics ContributionMagnetic Resonance Imaging Protocol Optimization for Delineation of Gross Tumor Volume in Hypopharyngeal and Laryngeal Tumors
Introduction
Delineation of the gross tumor volume (GTV) is the first and probably most important step in the radiotherapy treatment planning process. The capability of three-dimensional conformal therapy and especially intensity-modulated radiotherapy to conform the high-dose volume to the target volumes has further increased the importance of optimal imaging modalities. The introduction of computed tomography (CT) had a large impact on the accuracy of radiotherapy treatment, and CT is currently the standard imaging modality used for radiotherapy treatment planning of head-and-neck tumors. However, MRI has several benefits compared with CT, the most important being superior soft-tissue contrast. Other advantages of MRI are fewer dental-inlay artefacts compared with CT images and, in the case of laryngeal carcinoma, a higher sensitivity to detect tumor invasion of cartilage 1, 2. Other recent developments in MR imaging of laryngeal carcinoma include the potential to predict and monitor local tumor control 3, 4. A disadvantage of MRI, particularly in the region of the larynx, is the occurrence of motion artefacts caused by swallowing and tongue movements due to a longer scan time compared with CT (5).
In the literature there is no agreement on the value of MRI for the determination of the GTV in head-and-neck oncology. By 1988 Toonkel et al.(6) had already recommended MRI for patients needing complex radiotherapy planning for head-and-neck carcinoma. Rasch et al.(7) compared CT- and MR-based tumor delineations for advanced head-and-neck carcinoma and concluded that the delineated GTV and the interobserver variation were smaller for MR than for CT. Gordon et al.(8) investigated the interobserver variability of tumor volume determination for pharyngeal tumors and concluded that MRI-based tumor volumes are sufficiently reproducible. Geets et al.(9) compared MRI and CT for the delineation of pharyngeal–laryngeal tumors and concluded that MRI did not show a clinical advantage over CT in terms of volume determination and interobserver variability. The MR images in the latter study were, however, acquired using a multipurpose body coil in contrast to the other studies, which used dedicated head-and-neck coils generally used for diagnostic MRI. Unfortunately, the radiotherapy immobilization mask does not fit into the dedicated head-and-neck coils. Such a mask is required during MRI to guarantee the millimeter registration accuracy with CT images demanded for radiotherapy purposes.
We believe that these conflicting results can be explained by the relatively little attention paid to MRI protocol optimization, especially the choice of the optimal receiver coils. Currently various flexible surface coils are available, which allow optimal image quality in a dedicated region and are compatible with the use of an immobilization mask. Giron et al.(10) described the gain in signal-to-noise ratio (SNR) of these surface coils used in diagnosing laryngeal malignancies.
The aim of this study was to optimize and clinically test an MRI protocol for the delineation of hypopharyngeal and laryngeal GTVs for treatment planning purposes with the use of the radiotherapy positioning mask. Special attention was paid to the choice of the receiver coils. Furthermore, the influence of the magnetic field strength (1.5 T vs 3.0 T) on image quality was investigated.
Section snippets
Patient fixation
Magnetic resonance protocol optimization was done using a healthy volunteer with no pathology of the larynx. The final MRI protocol was tested on patients with hypopharyngeal and laryngeal carcinoma who were referred to our department for primary radiotherapy. The volunteer and the patients were fixed to a flat tabletop during MR scanning with the same immobilization mask that is used during radiotherapy treatment (five-point head-and-shoulder mask, Posicast PR5; Sinmed, Reeuwijk, The
Receiver coils
The image quality in terms of SNR at 1.5 T was greatly influenced by the type of receiver coil (Fig. 1). High-quality image values were obtained for the dedicated head-and-neck coil and surface coils. Images acquired with the body coil and the phased-array coil were not acceptable, mainly because the body coil senses a much larger volume than the surface coils. Images acquired using the surface coils yielded the highest SNR and CNR values, which were six to seven times higher than those for the
Discussion
The results of this study demonstrate that to utilize the full potential of MRI for radiotherapy purposes, the choice of receiver coils is crucial. The presence of the immobilization mask did not allow the use of dedicated head-and-neck coils that are used in diagnostic imaging. We found that the flexible surface coils offer a good alternative. They allow optimal image quality with sufficient coverage of the head-and-neck region. They can be easily mounted on the mask because of their flexible
References (11)
van den Brekel MW, Hermans R. Imaging of the larynx
Semin Roentgenol
(2000)- et al.
MRI assisted treatment planning for radiation therapy of the head and neck
Magn Reson Imaging
(1988) - et al.
The potential impact of CT-MRI matching on tumor volume delineation in advanced head and neck cancer
Int J Radiat Oncol Biol Phys
(1997) - et al.
Inter-observer variability in the delineation of pharyngo-laryngeal tumor, parotid glands and cervical spinal cord: Comparison between CT-scan and MRI
Radiother Oncol
(2005) - et al.
Variability of gross tumour volume delineation in head-and-neck cancer using CT and PET/CT fusion
Int J Radiat Oncol Biol Phys
(2006)
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Conflict of interest: none.