Radiation-induced DNA double-strand breaks in peripheral leukocytes and therapeutic response of heel spur patients treated by orthovoltage X-rays or a linear accelerator

PURPOSE: Biodosimetric assessment and comparison of radiation-induced deoxyribonucleic acid (DNA) double-strand breaks (DSBs) by γH2AX immunostaining in peripheral leukocytes of patients with painful heel spur after radiation therapy (RT) with orthovoltage X‑rays or a 6-MV linear accelerator (linac). The treatment response for each RT technique was monitored as a secondary endpoint. PATIENTS AND METHODS: 22 patients were treated either with 140-kV orthovoltage X‑rays (n = 11) or a 6-MV linac (n = 11) with two weekly fractions of 0.5 Gy for 3 weeks. In both scenarios, the dose was prescribed to the International Commission on Radiation Units and Measurements (ICRU) dose reference point. Blood samples were obtained before and 30 min after the first RT session. γH2AX foci were quantified by immunofluorescence microscopy to assess the yield of DSBs at the basal level and after radiation exposure ex vivo or in vivo. The treatment response was assessed before and 3 months after RT using a five-level functional calcaneodynia score. RESULTS: RT for painful heel spurs induced a very mild but significant increase of γH2AX foci in patients’ leukocytes. No difference between the RT techniques was observed. High and comparable therapeutic responses were documented for both treatment modalities. This trial was terminated preliminarily after an interim analysis (22 patients randomized). CONCLUSION: Low-dose RT for painful heel spurs with orthovoltage X‑rays or a 6-MV linac is an effective treatment option associated with a very low and comparable radiation burden to the patient, as confirmed by biodosimetric measurements.