Kitazato Yumiko, Kuga Noriyuki, Shirieda Katsutoshi, Enzaki Masahiro, Nakaguchi Yuji, Shimohigashi Yoshinobu, Kawasaki Toshihisa, Toyoda Masahiko, Kawahara Daisuke, Araki Fujio, Kawamura Shinji
Department of Image Inspection, Sagara Perth Street Clinic, Hakuaikai Social Medical Corporation.
Department of Radiology, University of Miyazaki Hospital.
Nihon Hoshasen Gijutsu Gakkai Zasshi. 2017;73(4):309-316. doi: 10.6009/jjrt.2017_JSRT_73.4.309.
Recently, intensity-modulated radiation therapy (IMRT) is used worldwide, highly accurate verification of the location using image-guided radiation therapy (IGRT) has become critical. However, the use of cone-beam computed tomography (CBCT) to ascertain the location each time raises concerns about its influence on radiotherapy dosage and increased radiation exposure. The purpose of this study was to measure the absorbed dose using nine kilovoltage (kV) devices and two megavoltage (MV) devices (total 11 devices) at eight facilities, compare the absorbed dose among the devices, and assess the characteristics of the respective devices to ensure optimal clinical operation. For the measurement of the absorbed dose, a farmer-type ionization chamber dosimeter, calibrated using a Co and an IMRT dose verification phantom manufactured from water-equivalent material RW3, was used to measure the absorbed dose at nine points in the phantom for two regions, the pelvic and cephalic region. The average absorbed dose of the pelvic region was 3.09±0.21 cGy in kV-CBCT (OBI), 1.16±0.16 cGy in kV-CBCT (XVI), 5.64±1.48 cGy in MV-CBCT (4 MV), and 6.33±1.54 cGy in MV-CBCT (6 MV). The average absorbed dose of the cephalic region was 0.38±0.03 cGy in kV-CBCT (OBI), 0.23±0.06 cGy in kV-CBCT (XVI), 4.02±0.72 cGy in MV-CBCT (4 MV), and 4.46±0.77 cGy in MV-CBCT (6 MV). There was a difference in the absorbed dose at the measured points as well as in the dose distribution in the phantom cross section. No major difference was observed in the absorbed dose among identical devices, but a difference was identified among the devices installed at multiple facilities. Therefore, the angle of rotation should be paid attention to when CBCT is taken, and the image-taking conditions should be determined. In addition, it is important to handle the devices only after ascertaining the absorbed dose of each device.
近年来，调强放射治疗（IMRT）在全球范围内得到应用，使用图像引导放射治疗（IGRT）对位置进行高精度验证变得至关重要。然而，每次使用锥形束计算机断层扫描（CBCT）来确定位置都会引发对其对放射治疗剂量的影响以及辐射暴露增加的担忧。本研究的目的是在八个机构使用九台千伏（kV）设备和两台兆伏（MV）设备（共11台设备）测量吸收剂量，比较各设备之间的吸收剂量，并评估各设备的特性，以确保最佳临床操作。为测量吸收剂量，使用了一种经钴校准的农夫型电离室剂量仪以及一个由水等效材料RW3制成的IMRT剂量验证体模，在盆腔和头部两个区域的体模中的九个点测量吸收剂量。盆腔区域的平均吸收剂量在kV-CBCT（OBI）中为3.09±0.21 cGy，在kV-CBCT（XVI）中为1.16±0.16 cGy，在MV-CBCT（4 MV）中为5.64±1.48 cGy，在MV-CBCT（6 MV）中为6.33±1.54 cGy。头部区域的平均吸收剂量在kV-CBCT（OBI）中为0.38±0.03 cGy，在kV-CBCT（XVI）中为0.23±0.06 cGy，在MV-CBCT（4 MV）中为4.02±0.72 cGy，在MV-CBCT（6 MV）中为4.46±0.77 cGy。测量点处的吸收剂量以及体模横截面中的剂量分布存在差异。在相同设备之间未观察到吸收剂量的重大差异，但在多个机构安装的设备之间发现了差异。因此，进行CBCT扫描时应注意旋转角度，并确定图像采集条件。此外，在确定每个设备的吸收剂量后再操作设备很重要。
