Modern radiation therapy techniques are exceptionally flexible in the deposition of radiation dose in a target volume. Complex distributions of dose can be delivered reliably, so that the tumor is exposed to a high dose, whereas nearby healthy structures can be avoided. As a result, an increase in curative dose is no longer invariably associated with an increased level of toxicity. This modern technology can be exploited further by modulating the required dose in space so as to match the variation in radiation sensitivity in the tumor. This approach is called dose painting. For dose painting to be effective, functional imaging techniques are essential to identify regions in a tumor that require a higher dose. Several techniques are available in nuclear medicine and radiology. In recent years, there has been a considerable research effort concerning the integration of magnetic resonance imaging (MRI) into the external radiotherapy workflow motivated by the superior soft tissue contrast as compared to computed tomography. In MRI, diffusion-weighted MRI reflects the cell density of tissue and thus may indicate regions with a higher tumor load. Dynamic contrast-enhanced MRI reflects permeability of the microvasculature and blood flow, correlated to the oxygenation of the tumor. These properties have impact on its radiation sensitivity. New questions must be addressed when these techniques are applied in radiation therapy: scanning in treatment position requires alternative solutions to the standard patient setup in the choice of receive coils compared to a diagnostic department. This standard positioning also facilitates repeated imaging. The geometrical accuracy of MR images is critical for high-precision radiotherapy. In particular, when multiparametric functional data are used for dose painting, quantification of functional parameters at a high spatial resolution becomes important. In this review, we will address these issues and describe clinical developments in MRI-guided dose painting.

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Dynamic contrast‐enhanced (DCE) MRI is useful for diagnosis, treatment monitoring and follow‐up of prostate cancer. However, large differences have been reported in the parameter range of the transfer constant Ktrans, making longitudinal studies and comparison of DCE‐MRI findings between studies difficult. Large part of this inconsistency in Ktrans values can be attributed to problems with the accurate measurement of the arterial input function (AIF) from the magnitude signal (AIFMAGN). Phase‐based AIF measurements (AIFPHASE) have been proposed as a more robust alternative to AIFMAGN measurements. This study compares AIFPHASE with AIFs measured with DCE‐CT (AIFCT), and the corresponding Ktrans maps in 12 prostate cancer patients. The shape of AIFPHASE and AIFCT are similar, although differences in the peak height and peak width exist as a result of differences in injection protocol. No significant differences in Ktrans values were found between the DCE‐MRI and DCE‐CT exams, with median Ktrans values of 0.10 and 0.08 min−1 for healthy peripheral zone tissue and 0.44 and 0.36 min−1 for regions suspected of tumor respectively. Therefore, robust quantification of Ktrans values from DCE‐MRI exams in the cancerous prostate is feasible with the use of AIFPHASE. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.

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Accurate prostate tumour detection with multiparametric magnetic resonance imaging: Dependence on histological properties, Acta Oncologica, 53:1, 88-95,