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

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, invitro 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 (=0.44 Gy-1, standard CI: 0.41-0.49 Gy-1) and are relatively insensitive to dose fractionation (/=16 Gy, standard CI: 12-34 Gy). The estimated repair half-time is 23min (standard CI: 10-97min) with some evidence that a small portion of the sublethal damage is repaired more slowly. Conclusion: The reported radiosensitivity parameters ( and /) are larger than those derived from other invitro experiments and clinical data. In contrast, the half-time for sublethal damage repair (23min) is close to the one derived from clinical data (16min). For such short repair half-times, the effectiveness of IMRT treatments may be substantially improved by decreasing the fraction delivery time.