Choline PET/MR of prostate cancer is a mismatch, but a valuable one

Quantitative values of simultaneous F-18 choline PET and diffusion-weighted imaging (DWI) do not correlate in the assessment of intermediate prostate cancer—perhaps because the measurements characterize different tumor biology, according to a study published last month in PLOS ONE.

A team of researchers including Axel Wetter, MD, from the department of diagnostic and interventional radiology and neuroradiology at the University Hospital Essen in Essen, Germany, evaluated the standard uptake value (SUV) of F-18 choline PET and apparent diffusion coefficient (ADC) of simultaneous MR in patients with intermediate primary prostate carcinoma to gain a better understanding of the relationship between the two values.

F-18 choline is still an investigational radiotracer and more research would be required before choline PET/MR could enter general clinical practice in this context. Some studies have indicated that choline PET may not have the specificity needed to discern tumor tissue from healthy tissue, but some data suggest that choline performs better for the evaluation of prostate cancer.

“Particularly for the detection and characterization of intermediate and high risk prostate carcinomas choline PET seems to be advantageous,” wrote the researchers. “Furthermore, choline PET appears to allow a monitoring of hormonal treatment by indicating a decrease in choline metabolism as a response to hormonal therapy.”

A total of 35 patients were included in the prospective study and underwent choline PET/MR. Of these, 21 were noted as high risk and not taking hormone therapy. Results of the study revealed 32 lesions. However, SUV was found to have no link to ADC, unlike some previous studies that showed an inverse correlation between ADC and grade of malignancy. ADC also has been gaining attention for its apparent usefulness in treatment monitoring.

“In oncologic imaging, the ADC can be used as an indicator of therapeutic response during chemotherapy, as it has been reported that ADC values tend to rise under ongoing treatment,” wrote Wetter et al. “This can be explained with a disintegration and decrease of tumor cells leading to an alleviation of water diffusion. The successful application of DWI for evaluation of treatment response has been shown for a variety of different tumors, including liver metastases, gynecological malignancies and head and neck cancer.”

The lack of correlation between measurements does not cast a negative light on the pairing. In fact, it could be their strength.

“The fact that SUVs and ADC values do not correlate in primary prostate cancers might offer a complementary value of both methods in such a way that both methods reflect different types of response to therapy and therefore might allow a more differentiated evaluation of treatment success.”