Palta J R, Hogstrom K R, Tannanonta C
Med Phys. 1984 Jul-Aug;11(4):498-501. doi: 10.1118/1.595543.
The McCall method has been used to measure neutron leakage from the Mevatron 77, 18- and 15-MV photon beams. Gold foil activation has been used employing a beta counting technique for the 18-MV beam and a gamma counting technique for both the 18- and 15-MV beam. The two counting techniques were used to evaluate their relative merit. The measurements were made at various locations in the patient-treatment plane for different field sizes. The results show that the thermal-neutron dose equivalent contributes only about 1%-2% of the total neutron dose equivalent. At 100 cm, the neutron dose equivalent for the 18-MV beam is approximately six times that of the 15-MV beam, slightly exceeding the 0.1% of the useful beam criteria used by some of the regulatory agencies. In light of the uncertainty in fluence to dose equivalent conversion factors, the increased dose equivalent above 0.1% is insignificant.
麦考尔方法已被用于测量米瓦特龙77的18兆伏和15兆伏光子束的中子泄漏情况。对于18兆伏的射线束，采用了金箔活化法并运用β计数技术；对于18兆伏和15兆伏的射线束，则采用了γ计数技术。运用这两种计数技术来评估它们各自的优缺点。在患者治疗平面的不同位置针对不同的射野大小进行了测量。结果表明，热中子剂量当量仅占总中子剂量当量的约1% - 2%。在100厘米处，18兆伏射线束的中子剂量当量约为15兆伏射线束的六倍，略超过一些监管机构所采用的有用射线标准的0.1%。鉴于注量到剂量当量转换因子存在不确定性，高于0.1%的剂量当量增加量微不足道。
