Tomiyama Yuuki, Araki Fujio, Oono Takeshi, Hioki Kazunari
Graduate School of Health Sciences, Kumamoto University, 4-24-1 Kuhonji, Kumamoto, Japan,
Radiol Phys Technol. 2014 Jul;7(2):303-9. doi: 10.1007/s12194-014-0266-1. Epub 2014 May 6.
Our purpose in this study was to implement three-dimensional (3D) gamma analysis for structures of interest such as the planning target volume (PTV) or clinical target volume (CTV), and organs at risk (OARs) for intensity-modulated radiation therapy (IMRT) dose verification. IMRT dose distributions for prostate and head and neck (HN) cancer patients were calculated with an analytical anisotropic algorithm in an Eclipse (Varian Medical Systems) treatment planning system (TPS) and by Monte Carlo (MC) simulation. The MC dose distributions were calculated with EGSnrc/BEAMnrc and DOSXYZnrc user codes under conditions identical to those for the TPS. The prescribed doses were 76 Gy/38 fractions with five-field IMRT for the prostate and 33 Gy/17 fractions with seven-field IMRT for the HN. TPS dose distributions were verified by the gamma passing rates for the whole calculated volume, PTV or CTV, and OARs by use of 3D gamma analysis with reference to MC dose distributions. The acceptance criteria for the 3D gamma analysis were 3/3 and 2 %/2 mm for a dose difference and a distance to agreement. The gamma passing rates in PTV and OARs for the prostate IMRT plan were close to 100 %. For the HN IMRT plan, the passing rates of 2 %/2 mm in CTV and OARs were substantially lower because inhomogeneous tissues such as bone and air in the HN are included in the calculation area. 3D gamma analysis for individual structures is useful for IMRT dose verification.
本研究的目的是对感兴趣的结构（如计划靶体积（PTV）或临床靶体积（CTV））以及危及器官（OAR）进行三维（3D）伽马分析，以用于调强放射治疗（IMRT）的剂量验证。在Eclipse（瓦里安医疗系统公司）治疗计划系统（TPS）中，使用解析各向异性算法并通过蒙特卡罗（MC）模拟计算了前列腺癌和头颈部（HN）癌患者的IMRT剂量分布。在与TPS相同的条件下，使用EGSnrc/BEAMnrc和DOSXYZnrc用户代码计算MC剂量分布。前列腺癌的处方剂量为76 Gy/38次分割，采用五野IMRT；HN癌的处方剂量为33 Gy/17次分割，采用七野IMRT。通过3D伽马分析，参照MC剂量分布，利用整个计算体积、PTV或CTV以及OAR的伽马通过率来验证TPS剂量分布。3D伽马分析的验收标准为剂量差异3/3以及一致性距离2%/2 mm。前列腺IMRT计划中PTV和OAR的伽马通过率接近100%。对于HN IMRT计划，CTV和OAR中2%/2 mm的通过率显著较低，因为计算区域中包含了HN中诸如骨骼和空气等不均匀组织。对单个结构进行3D伽马分析对IMRT剂量验证很有用。
