钻机换源后射野的质量控制与质量保证

目的：测量换源后钴机的灯光野与射野的符合性和射野半影大小，评价其能否适合运用于临床治疗。方法：选择5个射野面积分别为：3 cm × 3 cm，5 cm × 5 cm，10 cm × 10 cm，15 cm × 15 cm，20 cm × 20 cm；在深度为82、85、90 cm三个深度放置剂量验证胶片，钴机照射每张胶片时间为1 min；分析每张剂量验证胶片半影（P80% ～ 20%）大小以及灯光野与射野的符合性。结果：半影大小随照射野面积和深度增大而增大，最小为6 mm，最大为16.8 mm；灯光野与射野的符合性在y轴上较好，在x轴方向，灯光野相对于射野向x负方向偏移，最大为1.2 mm。结论：该钴机改装后，半影大小以及灯光野与射野的符合性达到GBZT161-2004医用γ射束远距治疗防护与安全标准，可用于临床治疗。

Quality control and quality assurance of the source-changed cobalt machine

Objective： To measure the penumbra of field and check the alignment of light field with radiation field （ALFRF） to make sure the source-changed cobalt machine wis suitable for clinic therapy. Methods： Films placed at the depths of 2 cm, 5 cm, and 10cm with the field sizes of 3 cm × 3, 5 cm × 5 cm, 10 cm × 10 cm, 15 cm × 15 cm, 20 cm × 20 cm2 were irradiated for 1 minute, then the penumbra （P80%～20%） were measured and ALFRF were checked. Results： The width of penumbra increased with the increase of the size of field and depth; the maximal was 16.8 mm and the minimal was 6 mm. In y-axis, the ALFRF was better and in x-axis, the light field moved slightly to the left, and the maximal distance between the light field and radiation field was 1.2 mm. Conclusion： The penumbra of field and the ALFRF accord with the safe criterion of GBZT 161-2004, and the source-changed cobalt machine can be used for clinical radiotherapy.