In vitro determination of radiation sensitivity parameters for DU-145 prostate cancer cells

Abstract

Purpose: The prolonged delivery times associated with intensity modulated radiation therapy (IMRT) may reduce treatment effectiveness of radiation therapy for cancers with short repair half-times. In this study, in vitro radiation experiments with DU-145 prostate cancer cells were designed to quantify the half-time of sublethal damage repair.Method and materials: A series of single-fraction and split-dose clonogenic survival experiments were performed and analyzed using the linear-quadratic (LQ) survival model with mono-/two-component exponential and reciprocal-time repair kinetic models.Results: Our data indicate that DU-145 cells are very radiosensitive (α = 0.44 Gy−1, standard CI: 0.41–0.49 Gy−1) and are relatively insensitive to dose fractionation (α/β = 16 Gy, standard CI: 12–34 Gy). The estimated repair half-time is 23 min (standard CI: 10–97 min) with some evidence that a small portion of the sublethal damage is repaired more slowly.Conclusion: The reported radiosensitivity parameters (α and α/β) are larger than those derived from other in vitro experiments and clinical data. In contrast, the half-time for sublethal damage repair (∼23 min) is close to the one derived from clinical data (∼16 min). For such short repair half-times, the effectiveness of IMRT treatments may be substantially improved by decreasing the fraction delivery time.