RESUMO
OBJECTIVE: To compare the dosimetric parameters of different radiotherapy plans [helical tomotherapy (HT), volume-modulated arc therapy (VMAT), and fixed-field intensity-modulated radiation therapy (FF-IMRT)] for locally advanced nasopharyngeal carcinoma (NPC). METHODS: A total of 15 patients with locally advanced NPC were chosen for this retrospective analysis and replanned for HT, VMAT, and FF-IMRT. The prescribed planning target volume (PTV) dose for the primary tumor and metastatic lymph nodes was 70 Gy (2.12 Gy/fraction, delivered over 33 fractions). The prescribed PTV dose for the high-risk subclinical region was 59.4 Gy (1.8 Gy/fraction, delivered over 33 fractions). The dosimetric parameters of the PTV and organs at risk (OARs) and the efficiency of radiation delivery were assessed and compared using the paired-samples t-test. RESULTS: Compared with VMAT and FF-IMRT plans, HT plans significantly improved the mean conformity index (CI) and homogeneity index (HI). The HT plans reduced the maximum doses delivered to OARs, such as the brainstem, spinal cord, and optic nerves, and significantly reduced the volume delivered to the high-dose region, especially when examining the V 30 value of the parotid glands. However, VMAT reduced the treatment time and improved the efficiency of radiation delivery compared with HT. CONCLUSIONS: For locally advanced NPC, the results showed that HT and VMAT possessed better target homogeneity and conformity, reducing the dose delivered to OARs compared with conventional FF-IMRT, with HT achieving the best effect. Among the techniques studied, VMAT had the shortest radiation delivery time. The results of this study can provide guidance for the selection of appropriate radiation technologies used to treat patients with locally advanced NPC who are undergoing concurrent chemoradiotherapy.
RESUMO
Objective This study aims to compare the advantages and disadvantages of the three techniques in improving the target volume dose and protecting the auris media cavity and eustachian tube isthmus region by investigating the dosimetric differences of three whole-brain radiotherapy techniques. Methods Thirty patients with whole brain metastases were randomly selected to design fixed field intensity modulated radiotherapy (ff-IMRT) plan, volumetric arc modulated therapy (VMAT) and three-dimensional conformal radiotherapy (3DCRT) plan, and to meet a 95% PTV prescription dose (40 Gy). The dosimetric parameters and monitor units of the target volume and organ at risk (OAR) in the three groups of treatment plans were compared and analyzed. Results The Conformity Index (CI) of the ff-IMRT plan (0.93 ± 0.02) was better than the VMAT plan (0.89 ± 0.01) and the 3DCRT plan (0.73 ± 0.03), respectively, and the difference was statistically significant (P < 0.05). The Homogeneity Index (HI) of the three plans were ff-IMRT (0.05 ± 0.01)、VMAT(0.08 ± 0.1) and 3DCRT (0.08 ± 0.01), respectively, and the difference was not statistically significant (P > 0.05). The Gradient Index (GI) were ff-IMRT (1.77 ± 0.1), VMAT (1.61 ± 0.07), 3DCRT (1.39 ± 0.08), respectively. The difference was statistically significant (P < 0.05). The monitor units (MU) were ff-IMRT (1551.97 ± 85.02), VMAT (303.7 ± 24.28) and 3DCRT (226.2 ± 2.5), respectively, the difference was statistically significant (P < 0.05). The Dmax of the middle ear of the three plans were ff-IMRT (2557.54 ± 477.39) cGy, VMAT (3107.9 ± 362.28) cGy, 3DCRT (4055.37 ± 71.45) cGy, respectively. The Dmax of the eustachian tube isthmus were ff-IMRT (2425 ± 380.4) cGy, VMAT (2902.4 ± 526.3) cGy and 3DCRT (3862.7 ± 135.9) cGy, the difference were statistically significant (P < 0.05). Conclusion In whole-brain radiotherapy, ff-IMRT and VMAT significantly reduced the dose of the bilateral middle ear cavities and eustachian tube isthmus compared with 3DCRT. VMAT is recommended for WBRT for reducing the number of monitor units significantly.
