Dosimetric study on middle ear with three whole-brain radiotherapy techniques / 中国辐射卫生

ABSTRACT

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.