Dosimetric study of influence of intensity modulated radiotherapy for nasopharyngeal carcinoma on hippocampal formation

Objective: To evaluate the dosimetric characteristics of hippocampal formation (HF) in the intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). Methods: Fifty-nine NPC patients underwent IMRT. Simultaneous integrated boost technology was used to determine the doses for the target areas. The dose ranges of the HF were collected by dose-volume histogram. The influence of T stage on the exposure doses (D_max, D_mean, D₂₀, V₁₀, V₂₀, V₃₀, and V₄₀) were compared. Results: The maximum dose for the HF (D_max) ranged from 11.1 to 78.2 Gy (F=24.2, P<0.05) and the D_mean ranged from 3.2 to 44.6 Gy (F=16.3, P<0.05). The D_max and D_mean of the T_1-2 stage patients were (40.8 ±9.4) Gy and (12.5 ±5.1) Gy, respectively, both significantly lower than those of the T_3-4 stage patients [(58.6± 14.8) Gy, (20.9± 9.3) Gy]. The mean exposed volume of the T₄ stage patients was significantly larger than that of the T₁ and T₂ stages patients. Conclusions: In the IMRT of NPC,the HF receives rather high irradiation dose. T stage is the main factor influencing the dose, especially T₃ and T₄ stages deserve serious attention. (authors)