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British Journal of Radiology (2006) 79, S2-S15
© 2006 British Institute of Radiology
doi: 10.1259/bjr/41321492
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New developments in MRI for target volume delineation in radiotherapy

V S Khoo, FRACR, FRCR, MD 1,2 and D L Joon, FRACR 3

1 Royal Marsden Hospital, Institute of Cancer Research, Fulham Road, London SW3 6JJ, 2 University of Manchester, Manchester, UK, 3 Austin Health Radiation Oncology Centre, Heidelberg Repatriation Hospital, Victoria, Australia


Figure 1
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  		Figure 1. A comparison of sagittal views of the pelvis for prostate radiotherapy with(a) CT reconstructed from 2.5 mm slices and (b) MR image obtained in-plane in the same patient. Some of the relevant structures of interest for radiotherapy are labelled on the MR image. These structures are not visualized well enough on CT to provide confident determination of the prostate boundaries for radiotherapy.

 

Figure 2
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  		Figure 2. A comparison of coronal views of the pelvis for prostate radiotherapy with(a) CT reconstructed from 2.5 mm slices and (b) MR image obtained in-plane in the same patient. Definition of the prostate gland boundaries and the adjacent structures is better visualized on MRI than with CT.

 

Figure 3
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  		Figure 3. A case from a study of meningiomas of the skull base evaluating the differences between MRI and CT assessment of the clinical target volume(CTV) for radiotherapy. The 3D reconstructed view of the CT-defined CTV (red outlines) and MR-defined CTV (yellow outlines) illustrates the spatial differences in CTV definition by the two different imaging modalities where the MR-defined CTV demonstrates tumour extending laterally along the petrous ridge that was not seen using CT [15].

 

Figure 4
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  		Figure 4. A case of a base of tongue cancer imaged with(a) CT and (b) MRI showing a large mass on the left side of the oropharynx involving the base of tongue and the left tonsillar fossa with invasion of the left parapharyngeal space. The base of tongue mass extends past the midline. These features are better visualized using MRI than CT.

 

Figure 5
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  		Figure 5. A comparison of transaxial co-registered views of the pelvis for prostate radiotherapy with (a) CT and (b) MR in the same patient. The boundaries of the prostate are better visualized using MR than with CT, notably the anterior rectal wall/recto-vesical fasia and prostate capsule.

 

Figure 6
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  		Figure 6. Co-registered (a) CT and (b) MRI scans showing a rectal cancer in the lower rectum extending to the anorectal junction with invasion of the left posterolateral wall. This is easily seen on the T2 weighted MRI scan as a hyperintense signal region that is not visible on CT.

 

Figure 7
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  		Figure 7. An illustration of various forms of distortion in MRI using a phantom consisting of a coplanar array of water-filled tubes embedded within in a circular solid plastic (PMMA) block. System distortion effects are seen in the apparent curvature of the tubes at A and their disappearance at B, which was due to warping distortion of the imaging plane. Magnetic susceptibility differences due to the presence of the plastic support block at C give rise to object-induced distortions in the form of discontinuities at the point where each tube enters the support block [10]. (Reproduced with permission from Elsevier).

 

Figure 8
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  		Figure 8. A case example of the use of ultrasmall paramagnetic iron oxide(USPIO) in MRI to evaluate pelvic lymph nodes in a man with prostate cancer. In this case, the lymph nodes (thick arrow) pre-USPIO (a) returned a negative MR signal following USPIO administration (thin arrow (b)) indicating normal lymph node architecture. This was later confirmed on lymph node sampling.

 




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