Incidental Dose to the Hippocampus in Nasopharyngeal Carcinoma Patients Treated with Intensity-modulated Radiation Therapy/Volumetric Modulated Arc Therapy

A BSTRACT Introduction: Radiotherapy has a crucial role in treating nasopharyngeal carcinoma (NPC). The use of intensity-modulated radiation therapy/volumetric modulated arc therapy (IMRT/VMAT) technique in treating NPC has improved the outcome and reduced the toxicities. The nasopharynx is in proximity to the medial temporal lobe which may lead to a high risk of radiation injury to the hippocampus in patients with NPC. Damage to the hippocampus is known to alter learning and memory and likely to cause cognitive problems. Objectives: The objective of this study was to evaluate the incidental dose to the hippocampus in patients with NPC undergoing IMRT/VMAT. Materials and Methods: The study population comprised 21 patients with NPC treated with concurrent chemoradiation therapy to a total dose of 66–70 Gy using IMRT/VMAT technique. The right and left hippocampus were retrospectively delineated on the axial slices from the simulation computed tomography scan for each patient using the established anatomical guidelines with magnetic resonance imaging co-registration. The mean hippocampus volume, V 3 Gy , V 20 Gy , V 40 Gy , and V 60 Gy and the average mean (D mean ), minimum (D min ), and maximum (D max ) dose to the hippocampus were analyzed. Results: The mean hippocampus volume was 3.76 cm 3 . The average D mean , D min , and D max to the hippocampus were 15.677 Gy, 5.327 Gy, and 36.78 Gy, respectively. The mean V 3 Gy, V 20 Gy, V 40 Gy , and V 60 Gy were 88.64%, 33.04%, 4.81%, and 0.08%, respectively. Conclusion: The hippocampus is exposed to significant doses during the treatment of NPC by IMRT/VMAT. This warrants the need to delineate the hippocampus as an organ at risk while treating all head and neck cancers where the clinical target volumes reach the base of the skull to prevent neurocognitive decline.