T2* Imaging Assessment of Neoadjuvant Radiation Therapy Combined With Pharmacological Ascorbate in Extremity Soft-Tissue Sarcomas: A Pilot Study.

Background: Extremity soft-tissue sarcomas (STS) are commonly treated with neoadjuvant radiation therapy followed by surgical resection. However, the pathological near-complete response rate is low (9-25%). Noninvasive imaging assessment that predicts treatment response before and during treatment is desirable to optimize treatment regimens. This pilot study aimed to investigate the application of a quantitative MRI parameter, T2*, in assessing neoadjuvant radiation therapy combined with pharmacological ascorbate in extremity STS. Methods: This prospective cohort study included seven patients diagnosed with extremity STS and scheduled to receive neoadjuvant radiation therapy combined with pharmacological ascorbate. T2* maps were obtained from each patient before treatment (baseline MRI), two weeks after initiating treatment (on-treatment MRI), and before surgery (pre-surgery MRI). The T2* values within the tumor region were transformed into z-scores with respect to the normal- appearing tissue region. The voxel-wise z-scores within the tumor region were thresholded to generate masks representing significantly high (z-score>1.96) and low z-score (z-score<-1.96) voxels. The means of the total z-scores and within each of the significantly high and low z-score mask were computed. Their correlations with percent necrosis from pathological examination were evaluated using Spearman's rank correlation coefficient r. A correlation was considered as moderate or strong when r is higher than 0.6 and 0.8, respectively. A correlation was considered as fair or weak when r is below 0.6. Results: For the baseline and on-treatment MRIs, the means of the significantly high z-scores of the T2* measurements showed moderate correlations with percent necrosis (r = 0.68 and 0.6; p = 0.11 and 0.24). For the pre-surgery MRI, the means of the total and significantly high z-scores showed strong correlations with percent necrosis (r = 0.8 and 0.9; p = 0.13 and 0.08). Tumor volume and baseline MRI-based percent necrosis showed fair or weak correlations (r = 0.3-0.54; p = 0.24-0.68). Conclusion: T2* measurements prior to treatment, two weeks after initiating treatment, and before surgery showed moderate to strong correlations with percent necrosis. These results support the potential for using T2* mapping to predict and assess response to neoadjuvant radiation therapy combined with pharmacological ascorbate in extremity STS. Level of Evidence: IV.

Assessment of Gadobutrol Safety in Combination with Ionizing Radiation Using a Preclinical MRI-Guided Radiotherapy Model.

MR-linac technology enhances the precision of therapeutic radiation by clarifying the tumor-normal tissue interface and provides the potential for adaptive treatment planning. Accurate delineation of tumors on diagnostic magnetic resonance imaging (MRI) frequently requires gadolinium-based contrast agents (GBCAs). Despite generally being considered safe, previous literature suggests that GBCAs are capable of contrast-induced acute kidney injury (AKI). It is unclear if the risk for AKI is enhanced when GBCAs are administered concurrently with ionizing radiotherapy. During irradiation, gadolinium may be liberated from its chelator which may induce AKI. The goal of this work was to determine if radiation combined with GBCAs increased the incidence of AKI. Using a preclinical MRI-guided irradiation system, where MRI acquisitions and radiation delivery are performed in rapid succession, tumor-bearing mice with normal kidney function were injected with GBCA and treated with 2, 8 or 18 Gy irradiation. Renal function was assessed on days three and seven postirradiation to assess for AKI. No clinically relevant changes in blood urea nitrogen and creatinine were observed in any combination of GBCA and radiation dose. From these data, we conclude that GBCA in combination with radiation does not increase the risk for AKI in mice. Additional investigation of multiple doses of GBCA administered concurrently with irradiation is warranted to evaluate the risk of chronic kidney injury.

Assessment of the Stability of Supraphysiological Ascorbate in Human Blood: Appropriate Handling of Samples from Clinical Trials for Measurements of Pharmacological Ascorbate.

Based on encouraging results from several early-phase clinical trials, there is renewed interest in the use of pharmacological ascorbate (i.e., intravenous administration resulting in >≈10 mM plasma ascorbate concentrations) in combination with standard-of-care cancer treatments including radiation and/or chemotherapy. Under normal, healthy physiological conditions, humans maintain plasma ascorbate concentrations in the range of 40-80 lM. However, in vivo antitumor activity requires supraphysiological plasma concentrations on the order of ≈20 mM. The stability of ascorbate in whole blood has been well studied. The goal of this work was to determine the appropriate handling methods of blood samples, after treatment with pharmacological ascorbate, which allow for the optimal measurement of ascorbate in plasma for dosing verification. Our findings indicate that ascorbate concentrations (mM) are relatively stable in whole blood collected in sodium heparin tubes and stored on ice (or at 4°C) for up to 24 h. After 24 h, ascorbate levels in plasma are relatively stable at 4°C for up to 72 h. At -20°C, plasma concentrations are relatively stable for 2-3 weeks, while at -80°C, ascorbate concentrations in plasma are stable for at least one month. In contrast, patient samples showed better stability when stored as whole blood compared to plasma at 4°C but increasing hemolysis over time may significantly skew ascorbate measurements. Additionally, patient samples can be reliably stored as plasma at -20°C for up to three weeks in either a frost-containing or frost-free environment. This information can guide the collection, processing and storage of clinical samples after pharmacological ascorbate infusions amenable to multi-center clinical trials.