Investigating γ H2AX as a Biomarker of Radiosensitivity Using Flow Cytometry Methods.

Background and Purpose. This project examined the in vitro   γ H2AX response in lymphocytes of prostate cancer patients who had a radiosensitive response after receiving radiotherapy. The goal of this project was to determine whether the γ H2AX response, as measured by flow cytometry, could be used as a marker of individual patient radiosensitivity. Materials and Methods. Patients were selected from a randomized clinical trial evaluating the optimal timing of Dose Escalated Radiation and short-course Androgen Deprivation Therapy. Of 438 patients, 3% developed Grade 3 late radiation proctitis and were considered to be radiosensitive. Blood was drawn from 10 of these patients along with 20 matched samples from patients with Grade 0 proctitis. Dose response curves up to 10 Gy along with time response curves after 2 Gy (0-24 h) were generated for each sample. The γ H2AX response in lymphocytes and lymphocyte subsets was analyzed by flow cytometry. Results. There were no significant differences between the radiosensitive and control samples for either the dose course or the time course. Conclusions. Although γ H2AX response has previously been demonstrated to be an indicator of individual patient radiosensitivity, flow cytometry lacks the sensitivity necessary to distinguish any differences between samples from control and radiosensitive patients.