Abstract
PurposeThe objective of this study was to evaluate the dosimetric feasibility of using hippocampus (HPC) sparing intensity-modulated radiotherapy (IMRT) in patients with locally advanced nasopharyngeal carcinoma (NPC).Materials/MethodsEight cases of either T3 or T4 NPC were selected for this study. Standard IMRT treatment plans were constructed using the volume and dose constraints for the targets and organs at risk (OAR) per Radiation Therapy Oncology Group (RTOG) 0615 protocol. Experimental plans were constructed using the same criteria, with the addition of the HPC as an OAR. The two dose-volume histograms for each case were compared for the targets and OARs.ResultsAll plans achieved the protocol dose criteria. The homogeneity index, conformity index, and coverage index for the planning target volumes (PTVs) were not significantly compromised by the avoidance of the HPC. The doses to all OARs, excluding the HPC, were similar. Both the dose (Dmax, D2%, D40%, Dmean, Dmedian, D98% and Dmin) and volume (V5, V10, V15, V20, V30, V40 and V50) parameters for the HPC were significantly lower in the HPC sparing plans (p<0.05), except for Dmin (P = 0.06) and V5 (P = 0.12).ConclusionsIMRT for patients with locally advanced NPC exposes the HPC to a significant radiation dose. HPC sparing IMRT planning significantly decreases this dose, with minimal impact on the therapeutic targets and other OARs.
Highlights
Several clinical studies have suggested that radiation-induced hippocampus (HPC) injury may play a considerable role in the neurocognitive decline of patients after cranial irradiation, deficits in learning, memory, and spatial processing [1,2]
Recent preclinical studies have demonstrated that a neural stem cell compartment in the HPC is central to the pathogenesis of neurocognitive deficits observed after cranial irradiation [3,4]
Due to the important role of the HPC in neurocognitive function, clinical trials, such as Radiation Therapy Oncology Group (RTOG) 0933, have been conducted in an effort to decrease the dose to the HPC during cranial irradiation and to mitigate radiation-induced neurocognitive toxicity [5]
Summary
Several clinical studies have suggested that radiation-induced hippocampus (HPC) injury may play a considerable role in the neurocognitive decline of patients after cranial irradiation, deficits in learning, memory, and spatial processing [1,2]. Deficits in cognitive function have been reported in patients with NPC after radiotherapy. Lee et al [7] found that after a median of 5.5 years after radiation, 16 NPC patients demonstrated poorer memory and social comprehension than a similar group of patients who were evaluated prior to irradiation. Other studies have shown that irradiation of the HPC is associated with pronounced cognitive impairment in the learning and memory domains in patients receiving radiotherapy for NPC [8,9]
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