Non-invasive pre-clinical MR imaging of prostate tumor hypoxia for radiation therapy prognosis

Abstract

Purpose: To investigate the usefulness of Oxygen-Enhanced Magnetic Resonance Imaging (OE-MRI) changes in signal intensity related to oxygen challenge for predicting tumor response to radiation therapy. Methods : Dynamic MR signal changes were acquired using Varian 4.7T small animal MR scanner prior to image-guided radiation therapy (IGRT) of small ( n = 6) and large subcutaneous ( n = 5) prostate tumors in adult male rats. An interleaved blood-oxygen level dependent (BOLD) and tissue-oxygen level dependent (TOLD) data acquisition or (IBT) was performed using a baseline of medical air as positive control and using medical oxygen as a breathing challenge. BOLD used a 2-D multi-slice spoiled gradient-echo with multi-echo sequence. TOLD used a 2-D multi-slice spoiled gradient-echo sequence. Voxel changes in signal intensity were determined by a correlation coefficient mapping technique. Irradiation technique planned consisted of 1F × 15 Gy AP/PA or 2F × 7.5 Gy AP/PA to the gross tumor volume (GTV). Tumor growth measurements were recorded over time to assess the response to IGRT. Results: BOLD and TOLD signals variously illustrated positive or negative impulse responses in the tumor ROI due to inhaling medical oxygen. Correlation coefficient mapping demonstrated heterogeneity in tumors after inhaling medical oxygen. BOLD and TOLD signals exhibited increased changes in signal intensities after the first fraction of dose. Multi-fractionation had minimum effect until the second fraction of dose was applied. Tumor growth delays were observed when inhaling medical oxygen during IGRT. Conclusion : OE-MRI is a non-invasive imaging modality that can provide insight to the oxygen status of tumors. Observed increase percent changes in BOLD and TOLD signal intensities after the first fraction of dose suggest tumors experienced reoxygenation. OE-MRI could be used for predicting tumor response to IGRT when using medical oxygen for increasing GTV radiosensitivity, suggesting patient stratification for clinical implementation. ------------------------------ Cite this article as: White DA, Mason RP. Non-invasive pre-clinical MR imaging of prostate tumor hypoxia for radiation therapy prognosis. Int J Cancer Ther Oncol 2014; 2(2):020243. DOI: 10.14319/ijcto.0202.43