Isobe Tomonori, Mori Yutaro, Takei Hideyuki, Sato Eisuke, Tadano Kiichi, Kobayashi Daisuke, Tomita Tetsuya, Sakae Takeji
Faculty of Medicine, University of Tsukuba.
University of Tsukuba Hospital.
Igaku Butsuri. 2016;36(3):156-160. doi: 10.11323/jjmp.36.3_156.
Conversion from CT value to density is essential to a radiation treatment planning system. Generally CT value is converted to the electron density in photon therapy. In the energy range of therapeutic photon, interactions between photons and materials are dominated with Compton scattering which the cross-section depends on the electron density. The dose distribution is obtained by calculating TERMA and kernel using electron density where TERMA is the energy transferred from primary photons and kernel is a volume considering spread electrons. Recently, a new method was introduced which uses the physical density. This method is expected to be faster and more accurate than that using the electron density. As for particle therapy, dose can be calculated with CT-to-stopping power conversion since the stopping power depends on the electron density. CT-to-stopping power conversion table is also called as CT-to-water-equivalent range and is an essential concept for the particle therapy.
从CT值转换为密度对于放射治疗计划系统至关重要。一般来说，在光子治疗中CT值会转换为电子密度。在治疗性光子的能量范围内，光子与物质之间的相互作用以康普顿散射为主，其截面取决于电子密度。通过使用电子密度计算比释动能率（TERMA）和核来获得剂量分布，其中比释动能率是从初级光子转移的能量，核是考虑散射电子的体积。最近，引入了一种使用物理密度的新方法。预计该方法比使用电子密度的方法更快且更准确。对于粒子治疗，由于阻止本领取决于电子密度，因此可以通过CT到阻止本领的转换来计算剂量。CT到阻止本领的转换表也称为CT到水等效范围，是粒子治疗的一个重要概念。
