Nair R P, Menon N S, Kartha M
Rev Interam Radiol. 1981 Jan;6(1):17-20.
The primary concern of all involved in the management of radiotherapeutic patients is that the tumor dose delivered to each and every patient in one institution is identical to that delivered anywhere else. Despite the advocacy 1,2,3,4 for the calibration of high energy photon beams at 5 cm depth or beyond in a water phantom to reduce the effect of electron "contamination" from collimators, filters, applicators, etc., the "in-air" method of calibration is still in vogue in many institutions in the United States and elsewhere. The introduction of S.I. units in radiology is likely to create ambiguity in proper conversion factors from exposure to absorbed dose which can be avoided if field instruments are calibrated in terms of absorbed dose in water under specified conditions. The present study shows that the estimated error can be as much as 7% low when the "in-air" method of calibration is used instead of measurements in a large water phantom at 5 cm depth for cobalt-60 photon beams and hence recommends that the procedure for "in-air" calibration for high energy photon beam should be discontinued.
参与放射治疗患者管理的所有人首要关心的是，在一个机构中给予每位患者的肿瘤剂量与在其他任何地方给予的剂量相同。尽管有观点主张在水模体中5厘米深度或更深位置校准高能光子束，以减少来自准直器、滤过器、施源器等的电子“污染”影响，但“空气校准”方法在美国和其他地方的许多机构中仍然流行。放射学中引入国际单位制可能会在从照射量到吸收剂量的适当转换因子方面造成混淆，如果在特定条件下根据水的吸收剂量校准野外仪器，这种混淆是可以避免的。本研究表明，对于钴-60光子束，使用“空气校准”方法而不是在5厘米深度的大水模体中进行测量时，估计误差可能低至7%，因此建议停止高能光子束的“空气校准”程序。
