Clinical applications for diffusion magnetic resonance imaging in radiotherapy

Abstract

In this article, we review the clinical applications of diffusion magnetic resonance imaging (MRI) in the radiotherapy treatment of several key clinical sites, including those of the central nervous system, the head and neck, the prostate, and the cervix. Diffusion-weighted MRI (DWI) is an imaging technique that is rapidly gaining widespread acceptance owing to its ease and wide availability. DWI measures the mobility of water within tissue at the cellular level without the need of any exogenous contrast agent. For radiotherapy treatment planning, DWI improves upon conventional imaging techniques, by better characterization of tumor tissue properties required for tumor grading, diagnosis, and target volume delineation. Because DWI is also a sensitive marker for alterations in tumor cellularity, it has potential clinical applications in the early assessment of treatment response following radiation therapy.

Fig 1

Diffusion abnormality index (DAI) of a patient with a brain metastasis treated with whole brain radiation therapy. DW MRI was obtained both pre RT (left column) and at the end of RT (right column). Top row: color-coded ADC maps; middle row: DAI maps; bottom row: zoomed DAI maps of the tumor. The tumor volume showed no significant change from pre RT to the end of RT. However, the DAI increased by 75% from pre RT to end of RT, suggesting tumor progression which was confirmed by post-Gd T1-weighted MRI one month post RT.

Fig 2

Tract-based statistical analysis (TBSS) of diffusion tensor images in patients receiving whole brain radiation therapy. There was a significant decrease in FA in the left inferior cingulum (left) and fornix columns (right) from pre RT to end of RT. Hot colors indicate a significant decrease in FA on the TBSS skeleton, and blue represents the TBSS skeleton without significant changes.

Fig 3

A 72-year-old patient with a serum PSA level of 4.1 ng/mL, the T2W imaging (left panel) showed a hypointense area in the left peripheral zone (arrow); discrimination of cancer from BPH in the transition zone was difficult. The ADC map (right panel) depicted a cancer focus in the anterior prostate as a hypointense area (arrow). Pathologic results revealed a cancer focus well correlated with the finding of the ADC map, but no malignancy was found in the left peripheral zone. Reprinted with permission from Miao et al in Eur J Radiol 2007;61:297–302.

Fig 4

A 66-year-old patient with prostate cancer: presurgical PSA, 5.52 ng/mL, clinical stage, T1C; surgical Gleason score, 3+4; and pathologic tumor volume, 4.77cm³. Whole-mount step-section histopathologic map shows prostate gland (a) Only one (of 12) slices shown; tumor was present on seven slices. (b) Closest transverse T2-weighted image corresponding to matching pathologic slice. (c) ADC map of slice in b. Reprinted with permission from Mazaheri et al in Radiology 2009;252:449–57.