Monitoring Radiation Therapy of Prostate Cancer by MRSI

Imaging procedures, such as magnetic resonance imaging (MRI) and magnetic resonance spectroscopic imaging (MRSI) may help doctors predict a patient's response to treatment and help plan the best treatment.

With six out of 10 years of data analyzed, DCTD-sponsored researchers have determined that pre-treatment endorectal MRI/MRSI findings using a standardized metabolic scoring system are predictive of outcome after external beam radiotherapy for prostate cancer, and that baseline MRI/MRSI data can be used for the planning of high dose brachytherapy. However, in order to use baseline MRI/MRSI data for radiation planning, it was necessary to correct for translations, rotations and deformations produced by the inflatable endorectal coil used in the staging MRI/MRSI exam.  Early after radiation therapy, prostatic citrate and polyamine levels were reduced or lost, followed by a slower decrease of choline and creatine, eventually resulting in an absence of all metabolism (metabolic atrophy).  Metabolic atrophy also significantly correlated with effective therapy using five-year PSA data as the standard of reference.  While regions of residual prostate cancer was identified by 3 or more consecutive voxels of elevated choline to creatine (Cho/Cr ≥ 1.5) with an overall accuracy of 81 percent using post radiation biopsy results as the standard of reference. After effective therapy, the metabolic resolution of cancer occurred earlier than PSA nadir.  Additionally, the time course of metabolic changes after therapy were different for brachytherapy and external beam radiation therapy. Preliminary ex vivo HR-MAS spectroscopic, pathologic and immunohistochemical data from post radiation biopsy samples suggest that residual disease can be distinguished from dying cancer and radiation atypia based on changes in total choline containing phospholipids containing metabolites and the phosphocholine (membrane synthesis) to glycerophosphocholine (membrane degradation) ratio.   All of the in vivo and ex vivo MRI/MRSI data has been incorporated into a web-based HIPPA compliant data base allowing for effective tracking of radiation patients, efficient data analysis, and the ability to share this data with outside researchers for further analysis and publication.

If the results of the first 6 years of research hold using 10-year outcome data, MRI/MRSI biomarkers may be useful for both selecting and planning radiation therapy, and assessing therapeutic effectiveness in individual patients.  This would have a significant impact on patient management and therapeutic trials of new approaches to radiation therapy.

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