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, 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 (alpha = 0.44 Gy(-1), standard CI: 0.41-0.49 Gy(-1)) and are relatively insensitive to dose fractionation (alpha/beta = 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 (alpha and alpha/beta) are larger than those derived from other in vitro experiments and clinical data. In contrast, the half-time for sublethal damage repair ( approximately 23 min) is close to the one derived from clinical data ( approximately 16 min). For such short repair half-times, the effectiveness of IMRT treatments may be substantially improved by decreasing the fraction delivery time.