Kouno Tomohiro, Araki Fujio, Nakaguchi Yuji, Oono Takeshi
Graduate School of Health Sciences, Kumamoto University.
Nihon Hoshasen Gijutsu Gakkai Zasshi. 2013 Jul;69(7):753-60. doi: 10.6009/jjrt.2013_jsrt_69.7.753.
Image-guided radiotherapy (IGRT) is an increasingly commonly adopted technique. As a result, however, total patient dose is increasing rapidly, especially when kV-cone beam computed tomography (CBCT) is applied. This study investigated the dosimetry of kV-CBCT using a Farmer ionization chamber with a (60)Co absorbed-dose calibration factor. The absorbed-dose measurements were performed using an I'mRT phantom (RW3, IBA) which is employed for dose verification of intensity-modulated radiotherapy (IMRT). The I'mRT phantom was used as a substitute for head and pelvis phantoms. The kV-CBCT absorbed dose was evaluated from a beam quality conversion factor of kV to (60)Co and the ionization ratio of the I'mRT phantom and water, calculated using the Monte Carlo method. The dose distribution in the I'mRT phantom was also measured using a radiophotoluminescent glass dosimeter (RGD). The absorbed doses for the pelvis phantom (full scan) ranged from 2.5-4 cGy for kV-CBCT and 4-8 cGy for MV-CBCT. TomoTherapy resulted in a lower dose of approximately 1.3 cGy due to fan-beam. For the head phantom (half scan), the doses ranged from 0.1-0.7 cGy for kV-CBCT and 3-5 cGy for MVCBCT. The results for RGD were similar to ion chamber measurements. It is necessary to decrease the absorbed dose of the organs at risk every time IGRT is applied.
图像引导放射治疗（IGRT）是一种越来越常用的技术。然而，结果是患者的总剂量正在迅速增加，尤其是在应用千伏锥形束计算机断层扫描（CBCT）时。本研究使用具有（60）钴吸收剂量校准因子的 Farmer 电离室研究了千伏 CBCT 的剂量学。吸收剂量测量使用 I'mRT 体模（RW3，IBA）进行，该体模用于调强放射治疗（IMRT）的剂量验证。I'mRT 体模被用作头部和骨盆体模的替代品。千伏 CBCT 的吸收剂量通过千伏到（60）钴的射束质量转换因子以及使用蒙特卡罗方法计算的 I'mRT 体模与水的电离比来评估。I'mRT 体模中的剂量分布也使用放射光致发光玻璃剂量计（RGD）进行测量。对于骨盆体模（全扫描），千伏 CBCT 的吸收剂量范围为 2.5 - 4 cGy，兆伏 CBCT 为 4 - 8 cGy。螺旋断层放射治疗（TomoTherapy）由于扇形束导致较低的剂量，约为 1.3 cGy。对于头部体模（半扫描），千伏 CBCT 的剂量范围为 0.1 - 0.7 cGy，兆伏 CBCT 为 3 - 5 cGy。RGD 的结果与电离室测量结果相似。每次应用 IGRT 时都有必要降低危及器官的吸收剂量。
