The Radiobiological Impact of Dental Root Filling Material in Intensity-Modulated Radiation Therapy (IMRT) in Patients with Nasopharyngeal Carcinoma

Regarding the possibility of perturbation due to the presence of dental root filling material (DFM) in treatment planning of patients with nasopharyngeal cancer, we aimed to evaluate the impact of this material on tumor control probability (TCP) and normal tissue complication probability (NTCP) using dose volume histograms (DVHs) of tumor and organ at risks, measured via treatment planning system. The optimization process of two intensity modulated radiotherapy (IMRT) techniques was performed by means of Prowess treatment planning system using 7- and 9-field 6-MV photons in two groups of 15 patients with nasopharyngeal cancer, with a difference in the presence or absence of DFM. After preparing DVHs, analysis and comparing of equivalent uniform dose (EUD), TCP, and NTCP were performed using Niemierko’s equivalent. Findings: In 9-field IMRT, there was statically significant decrease in mean EUD, TCP, and conformity index (CI) of tumor in patients with DFM; but there was no significant differences in homogeneity index (HI). Moreover, due to presence of DFM, there was statically significant increase in mean EUD and NTCP of mandible in both 7- and 9-field techniques, and in NTCP of left optic nerve in 9-field IMRT. Although for right eye, there was a statically significant decrease in NTCP by 7-field IMRT technique, due to presence of DFM. The effect of the presence of DFM on IMRT depends on field angles, and leads to significant decrease in TCP target volume, significant increase in NTCP of and EUD mandible and NTCP of left optic nerve, and significant decrease in NTCP of right eye.