Clinical Measurements of Oxygen via Electron Paramagnetic Resonance (EPR) During and after Breast Radiation Therapy: Preliminary Results of Baseline Evaluations and Response to Hyperoxygenation - Abstract
Purpose/Objectives: During radiation therapy (RT), patients often develop radiation-induced toxicities. EPR oximetry is an effective method for measuring oxygen levels. We present first-in-clinic data with sequential and repeated measurements of oxygen in normal breast tissue during and after whole breast radiotherapy. Materials/Methods: Nine patients undergoing RT for breast cancer were enrolled in a pilot study for EPR oximetry. Normal breast tissue of patients were injected with the EPR reporter material prior to whole breast RT. Tissue oxygenation was assessed using a clinical EPR oximeter. Patients were measured every week during RT and every 2-3 month follow-ups using EPR oximetry. Results: All patients, an average of 8-9 measurements was taken for a total of 73 measurements across patients. During their RT, the average baseline pO2 value across patients was 7 ± 3mmHg. When hyperoxygenation was applied, there was a statistically significant rise of 27mmHg (p = 0.005). Following completion of RT, the baseline and hyperoxygenation values were 11 ± 2mmHg and 25 ± 6 mmHg, respectively (p = 0.01). For both baseline and hyperoxygenation, no significant difference was observed between measurements taken during and after radiation therapy (p>0.1). Conclusions: Our preliminary data from nine patients have validated the feasibility and reproducibility of EPR oximetry to measure temporal changes in the oxygenation of normal breast tissue during and after an RT course. The results indicate that EPR oximetry may be used to in clinical trials to investigate oxygen levels and their response to potentially hyperoxygenation interventions, which could be very useful in determining the clinical efficacy of radiosensitization and the mechanism of fibrogenesis.