Evaluation of the effect of dental filling material on IMRT treatment planning in patient with nasopharyngeal cancer

Introduction: Presence of dental filling material (DFM) such as amalgam in treatment patient with nasopharyngeal cancer (NPC) is common. Streaking artifact Arising from this high density material in computed tomography (scan), may lead to perturbation in dose calculation and dose delivery. Widespread performance of intensity-modulated radiotherapy (IMRT) for NPC using anterior beams that pass through the part severely affected by artefacts prior to reaching the target volume, raise concern about the effect of dental amalgam. This study quantifies the effect of dental amalgam on dose distribution target volume and organ at risk, normal tissue complication probability (NTCP) and tumor control probability (TCP). Materials and Methods: IMRT optimization two groups of ۱۵ early-stage NPC patients with or without dental amalgam by prescribe ۷۰ Gy to planning target volume performed by using the prowess panther treatment planning system. We used one plan nine field arrangement (F۹E) and three plan of seven field (F۷, F۷E, F۷P) arrangement with different angle. The dose volume histograms (DVHs), monitor units (MUs), Homogeneity index (HI), conformity index (CI) and TCP of PTVs, NTCP spinal cord, brain stem and parotid gland were analyzed. Results: Mean dose PTV in F۷, FVE, F۷P and F۹E plan were ۷۱.۲۵±۱.۵۵, ۷۲.۰۶±۰.۹۶, ۷۱.۶۵ ±۱.۲۸ and ۷۱.۸۲±۰.۵۳ respectively in patients with DFM and ۷۱.۵۲±۱.۰۲, ۷۱.۵۱ ± ۰.۶۱, ۷۱.۳۰ ± ۰.۶۱ and ۷۱.۹۵ ± ۰.۸۰ in patient without DFM, Showing slight increase in mean dose of target volume. V۹۵ of PTV shows insignificant different in two group. Mean TCP in F۷, FVE, F۷P and F۹E plan were ۹۵.۰۶±۰.۴۵%, ۹۵.۱۸±۰.۵۴%, ۹۴.۹۳ ±۰.۶۸% and ۹۵.۰۵±۰.۴۲% in patient with DFM and ۹۴.۸۶±۰.۶۲%, ۹۴.۷۴ ± ۰.۴۳%, ۹۴.۸۰ ± ۰.۵۸% and ۹۵.۵۰ ± ۰.۴۰% in patient without DFM that shows insignificant different in two group. Mean HI of PTV-۷۰ in four plans in presence of DFM shows a slight decrease compared than the other. Mean and maximum dose Spinal cord, brain stem and parotid and their NTCP in presence of DFM show a slight decrease. Conclusion: According to the results, dental amalgam led to slight increase in TCP, mean dose target volume and slight decrease in mean dose some OARs and their NTCP. Average dose target volume and some organ at risk that consider for this study demonstrates no meaningful    difference exist in DVH and biological parameter in two group of patient.

کلیدواژه ها:

Nasopharyngeal carcinoma ، Intensity Modulated Radiation Therapy ، Dental filling material ، Treatment Planning ، Dose Distribution