Low-dose hyperradiosensitivity: is there a place for future investigation in clinical settings?

In vitro radiation doses of below 0.5 Gy have been shown to be more effective than higher doses per unit dose in killing clonogenic cells of many epithelial tumor cell lines. This phenomenon is known as low-dose hyperradiosensitivity. Preclinical studies have now suggested that there is synergism between chemotherapy and low-dose fractionated radiotherapy (LD-FRT). To test the clinical efficacy of this approach, we prospectively evaluated concurrent palliative chemotherapy and LD-FRT in patients with various types of epithelial tumors.

Patients suffering from relapses or metastases of epithelial tumors were scheduled to receive concurrent LD-FRT (two fractions of 0.4 Gy per day) and chemotherapy. Radiologic assessments were performed after three cycles of chemotherapy plus LD-FRT.

Between June 2006 and October 2007, 12 patients with lung cancer, 7 patients with head-and-neck tumors, 2 patients with breast cancer, and 1 patient with esophageal carcinoma, for a total patient population of 22, underwent concomitant LD-FRT and chemotherapy. All patients but 3 (86%) had received previous treatments for their cancer. The median total dose of LD-FRT delivered was 800 cGy (range, 320-1280 cGy). The overall response rate was 45% (42% in previously treated patients). Grade 3-4 hematologic toxicities (Radiation Therapy Oncology Group ratings) were observed in 2 patients. At a median follow-up of 6.5 months, however, no local toxicity was observed.

In our experience, concurrent LD-FRT and chemotherapy was well tolerated. Because the response rate seems promising, prospective Phase II studies of the strategy are now under way.