The Hippocampus Sparing Volume Modulated Arc Therapy does not Influence Plan Quality on Locally Advanced Nasopharyngeal Carcinoma Patients

Irradiation on hippocampus would lead to neuro-cognitive dysfunction in locally advanced nasopharyneal carcinoma (LA-NPC) patients accepting radiotherapy. Our study here aimed to investigate if undergoing hippocampus sparing (HS) volume modulated arc therapy (VMAT) would influence the plan quality in LA NPC patients. We designed three kinds of radiotherapeutic plans for 11 LA NPC patients: conventional VMAT (C-VMAT), HS-VMAT and HS intensity modulated radiation therapy with dynamic multileaf collimator (HS-dMLC). And the dose distribution on targets and surrounding organs at risk (OAR) were carefully evaluated. We found out that the expected doses on hippocampus were significantly lowered in HS-VMAT (899 ± 378 cGy) and HS-dMLC (896 ± 321 cGy) as compared to C-VMAT (1518 ± 337 cGy, p < 0.05), but meaningless difference was presented on plan quality of targets (p > 0.05). Moreover, lower radiation doses on brain stem were observed in HS-VMAT plan in comparison with C-VMAT plan (p < 0.05). However, there were no statistically meaningful diversities in the doses received by other OARs among all plans. Here we concluded that HS-VMAT presented promising advantages on protecting hipppcampus and brain stem as compared to C-VMAT and HS-dMLC, but enthusiastically had no effects on plan quality in LA-NPC patients.