穿透型参考电离室在立体定向放疗的相对剂量学中的应用

The application of transmission reference ionization chamber in the relative dosimetry of stereotatic radiotherapy

目的探讨Stealth穿透型参考电离室在立体定向放疗的相对剂量学中的实际应用价值。方法在IBA ■Blue Phanto m水箱中使用2种方法对于配备Brianlab■圆锥形限光筒的Varian ■ Novalis 6 MV光子射线进行相对剂量测定。第1种方法无Stealth穿透型参考电离室,单独使用SFD半导体电离室配合“Step by Slep”逐点测量;第2种方法有Stealth穿透型参考电离室,使用SFD半导体电离室配合"Continuous"连续测量测量内容包括直径4、15 mm限光筒下中心轴百分深度剂量(PDD)曲线和离轴剂量比(OAR)曲线并记录每次测量所需时间.结果对于配备直径4 mm及15 mm的X刀限光筒的6 MV光子射线,逐点测量和连续测量所得的射野中心轴PDD曲线及10cm深度处OAR曲线吻合度较好,差异在1%以内。连续测量PDD曲线及OAH曲线所需时间大幅缩短,较逐点测量平均缩短为13. 1%和20.7%结论Stealth穿透型参考电离室在立体定向放疗相对剂量学中的应用可以在保证剂量结果准确性前提下大幅提高测量效率.

Objective To investigate the applieatio n value of a transmission referr nee stealth ionization chamber in the relative dosimetry of stereotactic radiotherapy. Methods The relative dosage of Varian R Novalis 6 MV photon rays equipped with Brainlab ■ conical applicators was determined by two different approaches in the IBA ■ Blue Phantom. One approach was designed to utilize IBA ■ SFD3G semiconductor ionization chamber alone in the "step by step" measurenirnt mode, whereas the other method was to utilize IBA ■ SFD as the field detector combined with stealth ionization chamber as the reference detector in the "continuous" measurement mode. The central axial percentage depth dose ( PDD) and off axis ratio (OAR) in a diameter of 4 and 15 mm were measured and the time spent on each measurement was recorded. Results The PDDs at the cenlral axis and OARs at a depth of 10 cm for both conical applicators were in good agreement between the two measurement approaches with a dose difference of< 1%. The time spent on PDDs and OARs measurement with stealth ionization chamber was shortened by 13. 1% and 20. 7% compared with those without Stealth ionization chamber. Conclusion Stealth ionization chamber can be applied in the relative dosimetry of stereotactic radiotherapy with high dose accuracy and high efficiency.