Analysis of placement error affecting target volume in intensity-modulated radiotherapy for nasopharyngeal carcinoma / 中国医师进修杂志

ABSTRACT

Objective:To investigate the effect of placement error on target volume and critical structure in intensity modulated radiation therapy (IMRT) in patients with nasopharyngeal carcinoma.Methods:The study period was from January 2018n to March 2019.The 60 patients with nasopharyngeal carcinoma who were treated in Zhejiang Cancer Hospital for this period and received radiation therapy were treated with simultaneous integration and intensity-modulated radiation therapy.The total tumor volume and clinical setting were set. The target volume and low-risk lymph node area were 70.0, 59.4 and 54.0 Gy respectively, with a total of 33 divisions; 3, 5 and 10 mm were moved around the top, bottom, left and right to simulate the placement error; the average dose, the maximum dose, the planned target volume and >110% and <93% prescription dose were evaluated. For both parotid glands, the average dose and >50% parotid gland dose was evaluated; the maximum dose and 2 cc spinal cord tolerance dose were analyzed.Results:Compared with no displacement, the maximum percentage change in the average dose of the total tumor volume (GTV-70 Gy) at the center displacement of 3 mm was smaller (2.2%), and the maximum percentage changes of the average dose at the center displacement of 5mm and 10mm were 6.4% and 16.0% respectively.; Analysis of clinical target volume (CTV) and planned target volume (PTV) dose volume analysis of different displacements showed that the average volume of CTV-54 Gy was (112.06 ± 55.92) cc (range 50.6-243.8 cc), compared to V54 (%) The maximum percentage changes of center displacements of 3, 5 and 10 mm were 1.5%, 6.8% and 23.8%. The positioning error of 3mm along the posterior and lateral sides can significantly affected the dose of the spinal cord; the positioning error along the lateral and anterior directions could significantly affect the dose of the parotid glands on both sides. The maximum average dose produced by the left displacement under the same conditions was (46.38 ± 5.35) Gy.Conclusions:In the intensity-modulated radiotherapy for nasopharyngeal carcinoma, the position error should be confirmed regularly at the same time to achieve a better target volume dose and improve the treatment effect.