BeamModulator新型多叶准直器半影的测量

目的 探讨医科达Synergy-S直线加速器配备的微型多叶准直器的半影特性。 方法 利用PTW MP3 三维水箱和PinPoint电离室分别在水中和空气中测量6、10和18 MV X线的射野离轴比曲线,数据处理后得到半影,分析半影随射线能量、模体深度以及叶片位置的变化。结果 6 MV X线在空气中的半影比水中最大剂量深度处的半影小2 mm;叶片端面的半影比叶片侧面的半影大1 mm左右。微型多叶准直器的半影大小与射线能量、模体深度以及叶片位置均有关。相同照射条件下,射线能量从6 MV提高到18 MV,半影增加1~1.5 mm;模体深度从d_max增加至10 cm,半影增加了1.5 mm;叶片位置不同,半影相差1.5~2 mm。结论 叶片的半影与其机械设计与使用条件密切相关。吸收剂量计算和治疗计划设计时需要充分考虑多叶准直器的半影特性。

Penumbra measuremnts of BeamModulatorTM multileaf collimator

Objective To evaluate the penumbra of a new multileaf collimator equipped with Elekta Synergy accelerator.Methods The penumbra were derived from beam profiles measured in air and water using PinPoint ion chamber with PTW MP3 water phantom. Variations of penumbra with X-ray beam energy, depth in water, and leaf position were investigated.Results The penumbra in air for 6 MV X-ray was 2 mm less than that at depth of maximal dose in water. The penumbra of leaf side was 1 mm less than that of the leaf end. The penumbra had close relationship with beam energy, depth in water and leaf position. Penumbra was increased with beam quality and water depth. The leaf position had great influence on the penumbra.Conclusions The penumbra of the multileaf collimator is related to its original design and radiation delivery technique. Special considerations should be taken into during treatment planning. Regular measurement should be performed to guarantee the delivery quality.