Impact of Prolonged Fraction Delivery Time Modelling Stereotactic Body Radiation Therapy with High Dose Hypofractionation on the Killing of Cultured ACHN Renal Cell Carcinoma Cell Line

INTRODUCTION Stereotactic body radiotherapy delivers hypofractionated irradiation with high dose per fraction through complex treatment techniques. The increased complexity leads to longer dose delivery times for each fraction. The purpose of this study is to investigate the impact of prolonged fraction delivery time with high-dose hypofractionation on the killing of cultured ACHN cells. METHODS AND MATERIALS The radiobiological characteristics and repair half-time of human ACHN renal cell carcinoma cell line were studied with clonogenic assays. A total dose of 20 Gy was administered in 1, 2 or 3 fractions over 15, 30 or 45 min to investigate the biological effectiveness of radiation delivery time and hypofractionation. Cell cycle and apoptosis analysis was performed after 3-fraction irradiation over 30 and 45 min. RESULTS The α/β and repair half-time were 5.2 Gy and 19 min, respectively. The surviving fractions increased with increase in the fraction delivery time and decreased more pronouncedly with increase in the fraction number over a treatment period of 30 to 45 min. With increase in the total radiation time to 30 and 45 min, it was found that with the same total dose, 2- and 3-fraction irradiation led to more cell killing than 1-fraction irradiation. 3-fraction radiation induced G2/M arrest, and the percentage of apoptotic cells decreased when the fraction delivery time increased from 30 min to 45 min. CONCLUSION Our findings revealed that sublethal damage repair and redistribution of the cell cycle were predominant factors affecting cell response in the prolonged and hypofractionated irradiation regimes, respectively.