Intensity-modulated radiation therapy in nasopharyngeal carcinoma: virtual touch tissue quantification of submandibular gland

Objectives: The present study is to evaluate Virtual Touch Tissue Quantification (VTQ) technique in the prevention of submandibular gland damage in patients with Nasopharyngeal Carcinoma (NPC) after Intensity-Modulated Radiation Therapy (IMRT). Material and method: A total of 61 patients diagnosed with NPC were treated with IMRT. All the patients underwent Ultrasonography (US) while submandibular volume was determined and VQT examination while Shear Wave Velocity (SWV) was measured. For IMRT, the total cumulative dose of PGTVnx was 69.52-74.32 Gy/30-32f in 6-6.5 w. The follow-up lasted for 6 months. The doses of submandibular glands were analysed by Dose-Volume Histogram (DVH) on TPS system. The parameters were analysed by paired samples t-test, independent t-test, Pearson correlation, Receiver Operating Characteristics (ROC) curves and multiple logistic regression analysis using SPSS 22.0 software. Results: The volumes of submandibular glands in the planning target volume were decreased at the beginning of radiotherapy (P<0.05). The mean volumes of submandibular glands decreased from 9.485 ± 1.622 cm3 to 6.987 ± 1.069 cm3 at the end of radiotherapy, and 5.986 ± 0.827 cm3 at the 6th month after radiotherapy (P<0.05). The SWV value was 1.68 ± 0.21 m/s before radiotherapy, 2.38 ± 0.19 at the end of radiotherapy, and 2.52 ± 0.47 m/s at the 6th month after radiotherapy, respectively (P<0.05). The doses of Dmax, Dmean and D50 were 70.08 ± 4.08 Gy, 58.24 ± 3.66 Gy and 52.87 ± 2.18 Gy, respectively. The incidence rates of xerostomia were 59.02% and 54.10% at the end of radiotherapy and the 6th month after radiotherapy, respectively. The threshold values of Dmean and D50 for diagnosing postradiation xerostomia were 40.42 Gy and 36.38 Gy, respectively. Conclusions: The present study demonstrates that VQT technique can be used in the evaluation of the submandibular glands damages. It is effective in the prevention of postradiation xerostomia.