医用加速器碳纤维治疗床和固定底板盆腔部位对旋转射野及固定野吸收剂量的影响

Effect of carbon fiber treatment-table of medical accelerator and pelvic cavity with fixed baseplate on absorbed dose of rotating field and fixed field

目的:分析探讨医用加速器碳纤维治疗床和固定底板对旋转射野吸收剂量的影响。方法:采用同中心SCD100 cm照射,X射线能量为6 MV,每个射野机器跳数设置为100 MU,治疗床前后移动距离150 cm,将标准固体水模置于治疗床和固定底板上,使用FC65-G电离室测量吸收剂量,计算不同入射弧度和角度时治疗床及固定底板对X射线的透射率(F)值。分别采用旋转弧和固定野照射,旋转弧照射时将360°均分成4弧、8弧和12弧,记为弧度(ARC)4、ARC8和ARC12;固定野照射时,机架顺时针方向每隔10°测量190°~180°机架角转一周的吸收剂量,记为Fixed 36。结果:ARC4、ARC8和ARC12的3组实验中,射野面积越大,F值越高。固定野照射实验中,射野为10 cm×10 cm和20 cm×20 cm、机架角度为120°和对称方向240°时F值最小,分别为92.21%和92.96%。结论:治疗床在IMRT和VMAT治疗中的剂量衰减明显,基于治疗床和固定底板对固定野照射吸收剂量影响的基础上,对比分析旋转照射野穿透治疗床和固定底板的透射率,可为制作放射治疗计划时提供有益的参考。

Objective:To investigate effect of carbon fiber treatment-table of medical accelerator and pelvic cavity with fixed baseplate on absorbed dose of rotating field and fixed field.Methods:Adopted co-concentricity radiation with SCD100 cm,and the power of X-ray was 6 MV,and the hop count of each machine was 100 MU.The displacement distance between back and forth treatment-table was 150cm,and the solid water phantom of standard was placed at treatment-table and fixed baseplate,and the FC65-G ionization chamber was used to measure the absorbed dose,and the transmittivity values of treatment-table and fixed baseplate for X-ray at different radian and angle of incidence were calculated.The rotation arc and fixed field were respectively adopted in radiation.When rotation arc was used in radiation,360°was averagely divided into 4 arcs,8 arcs and 12 arcs and they were marked as ARC4,ARC8 and ARC12.When fixed field was used in radiation,the absorbed dose was measured per 10°as clockwise of rack from 190°to 180°when angle of rack rotated one round,and they were recorded as Fixed 36.Results:In the experiments of ARC4,ARC8 and ARC12,the F value of transmittivity was higher when the field area was larger.In the fixed field experiment,the transmittivities reached the minimum when fields were 10cm×10cm and 20cm×20cm,and when the angle of rack was 120°and the symmetry direction was 240°.And the transmittivities respectively were 92.21%and 92.96%.Conclusion:The dose attenuations of treatment-table in the intensity modulated radiation therapy(IMRT)and volumetric modulated arc therapy(VMAT)are significant.Based on the effects of treatment-table and fixed baseplate on absorbed dose of fixed field radiation,the analysis for transmittivity of rotation radiation field on treatment table and fixed baseplate can provide beneficial references for formulating radiotherapy plan.