Reirradiation Tolerance of the Human Brain

Purpose

To give an overview of current available clinical data on reirradiation of glioma with respect to the tolerance dose of normal brain tissue.

Methods and Materials

Clinical brain reirradiation studies from January 1996 to December 2006 were considered on radiation-induced late adverse effects—i.e., brain tissue necrosis. The studies were analyzed by using the linear quadratic model to derive information on the cumulative biologic effective tolerance dose (BED_cumulative) and equivalent doses in 2-Gy fractions (normalized total doses, NTD_cumulative) for the healthy human brain.

Results

The NTD_cumulative in conventional reirradiation series (NTD_cumulative of 81.6–101.9 Gy) were generally lower than in fractionated stereotactic radiotherapy (FSRT) (NTD_cumulative of 90–133.9 Gy.) or LINAC-based stereotactic radiosurgery series (NTD_cumulative of 111.6–137.2 Gy). No correlation between the time interval between the initial and reirradiation course and the incidence of radionecrosis was noted. The analysis showed the prescribed NTD_cumulative to increase with decreasing treatment volume, which is allowed by modern conformal radiation techniques.

Conclusion

Radiation-induced normal brain tissue necrosis is found to occur at NTD_cumulative >100 Gy. The applied reirradiation dose and NTD_cumulative increases with a change in irradiation technique from conventional to radiosurgery re-treatment, without increasing the probability of normal brain necrosis. Taken together, modern conformal treatment options, because of their limited volume of normal brain tissue exposure, allow brain reirradiation for palliative treatment of recurrent high grade glioma with an acceptable probability of radionecrosis.

Reirradiation, Tolerance dose, Brain, Late side effects, Normalized total dose