Feasibility of hippocampal dose-volume parameters associated with memory decline in intensity-modulated radiotherapy for supratentorial tumors.

The purpose of the present retrospective study was to evaluate the feasibility of hippocampal dose-volume parameters associated with memory decline for intensity-modulated radiotherapy (IMRT). In total, 18 patients who underwent IMRT for supratentorial tumors were analyzed. Prescribed doses of IMRT in 30 fractions were 60 Gy to planning target volume (PTV) 1 of the local area and 48-51 Gy to PTV2 of the extended local area. Based on previous literature, the present study investigated dose-volume parameters of the bilateral hippocampi: D40% of 13.1 Gy, D50% of 29.6 Gy, and V55Gy of 5.0%. It was evaluated which of the parameters was most achievable, and unfavorable factors that interfere with reaching these parameters were identified. As a result, D40% of 13.1 Gy, D50% of 29.6 Gy and V55Gy of 5.0% were achieved in 17, 67 and 33% of patients, respectively. For D50% of 29.6 Gy, PTV2 ≥500 cc (P=0.004) and tumor in temporal/corpus callosum/basal ganglia (P=0.009) were significant unfavorable factors. In conclusion, D50% of 29.6 Gy was most achievable. In daily clinical practice, it should be primarily attempted to achieve D50% of 29.6 Gy of the bilateral hippocampi.