基于Trilogy加速器的周边剂量学研究  

Peripheral dosimetry of a Trilogy accelerator

作　　者：杨波[1] 庞延田 孙显松 董婷婷[1] 罗春丽[1] 王冠群[1] 李洪明[1] 胡克[1] 邱杰[1] 张福泉[1] 

机构地区：[1]中国医学科学院北京协和医学院北京协和医院放疗科,北京100730

出　　处：《中华放射肿瘤学杂志》2016年第10期1108-1112,共5页Chinese Journal of Radiation Oncology

摘　　要：目的：研究不同条件下Trilogy加速器的周边剂量及Diode半导体电离室测量的可行性。方法在固体水测量模体中使用CC13空气电离室和Diode半导体电离室测量不同距离（1～31 cm共13个测量点）、深度（3、10、15 cm ）、射野大小（10、20、30 cm ）、楔形板（ W15、W45、VW15、VW45）、射线能量（6、18 MV）下的周边剂量分布。移除散射模体，测量其周边剂量与漏射剂量Dleakage和模体散射剂量 Dscat er之间关系。模拟宫颈癌放疗患者使用 VMAT、IMRTstepshoot、IMRTsliding window照射CRIS仿真模体，测量乳腺、甲状腺及晶体周边剂量。剂量归一于等中心点处。结果周边剂量随测量距离增加逐渐减小（由距射野边缘1 cm处的13.41％降至31 cm处0.25％），射野边缘相同距离处随深度增加基本无差异，30 cm射野约为10 cm射野的2倍。随物理楔形板角度增加逐渐增大，与开放野相比略增加1％；随虚拟楔形板角度增加而减小，与开放野相比降低2％～3％。6、18 MV X线下分别由1 cm处13.35％、11.06％衰减至31 cm处0.23％、0.20％。近射野边缘处Dscat er占主导地位，随距离由1 cm增加至25 cm，Dscat er所占比例约从62.45％降至5.71％。6 MV X线下所有测量结果中CC13电离室与Diode电离室的最大百分比偏差＜1％。 VMAT、IMRTstepshoot、IMRTsliding window模式下乳腺、甲状腺、晶体的分别为6.72、2.90、2.37 mGy，7.39、4.05、2.48 mGy，9.17、4.61、3.21 mGy。结论 CC13空气电离室和6 MV半导体电离室测量周边剂量具有较好一致性和可行性。临床治疗中了解周边剂量与不同照射条件关系有助于减少照射野外OAR剂量，采用屏蔽防护技术可进一步减少剂量沉积。Objective To determine the peripheral dose （ PD） of a Trilogy accelerator under different conditions and the feasibility of PD measurement using the semiconductor diode ionization chamber. Methods In a solid water phantom, a CC13 air-filled ionization chamber and a semiconductor diode ionization chamber were used for PD measurements with different distances （13 measurement locations within 1.31 cm） , depth （ 3, 5, 15 cm） , field sizes （ 10, 20, 30 cm） , wedge （ W15, W45, VW15, VW45） , and beam energy （6, 18 MV）. The relationship of PD with PDleakage and PDscat er was determined by removing the scatter phantom. Simulating the patients with cervical cancer undergoing radiotherapy, a CIRS phantom received volumetric modulated arc therapy （ VMAT） , step.shoot intensity.modulated radiotherapy （ IMRT） , and sliding.window IMRT to measure PDs of the breast, thyroid, and lens. All the data were normalized to the isocenter. Results PD was gradually reduced with the increase in distance （ 13.41% at 1 cm from the edge to 0.25% at 31 cm from the edge） . With a fixed distance from the edge of the radiation field, there was no significant difference in PD between different depths. A radiation field with a size of 30 cm had a PD about two-fold higher than that with a size of 10 cm. PD increased with the increase in the physical wedge angle and increased by 1% compared with the open field;PD decreased with the increase in the virtual wedge angle and decreased by 2-3% compared with the open field. PD decayed from 13.35% at 1 cm to 0.23% at 31 cm under 6 MV X-ray and from 11.06% at 1 cm to 0.20% at 31 cm under 18 MV X-ray. Dscat er was dominant in the regions close to the edge of radiation field and decreased from 62.45% at 1 cm to 5.71% at 25 cm. In all measurements under 6 MV X-ray, the maximum proportion difference between CC13 ionization chamber and diode ionization chamber was less than 1%. PDs of the breast, thyroid, and lens were 6.72, 2.90, and 2.37 mGy in VMAT mode, 7.39, 4.05, and 2.48

关 键 词：周边剂量 半导体电离室 空气电离室 固体水 仿真模体 

分 类 号：R730.55[医药卫生—肿瘤]