Freim J O, Feldman A
Med Phys. 1979 Nov-Dec;6(6):530-5. doi: 10.1118/1.594645.
Cobalt-60 dose determination can be accomplished by a variety of methods. This study investigates dose determination by actual "at-depth" measurement for the depths and field sizes desired as well as by "in-air" or "in-water" calibration measurements for both constant SSD and isocentric techniques. Comparison of the above dose determination methods reveals the existence of both depth-dependent and field size-dependent dose discrepancies between the individual methods studied. For many teletherapy units, the source of these discrepancies lies in the inapplicability of the tabulated percent depth dose and tissue-air ratio values employed. Appropriate percent depth dose and tissue-air ratios can be obtained by performing a series of at-depth dose determinations for a variety of depths and field sizes. When the appropriate values are employed, excellent agreement is found between all of the dose determination methods investigated.
钴-60剂量测定可通过多种方法实现。本研究调查了通过实际“深度处”测量来确定所需深度和射野大小的剂量，以及通过“空气中”或“水中”校准测量来确定等中心技术和固定源皮距技术的剂量。对上述剂量测定方法的比较表明，在所研究的各个方法之间存在与深度和射野大小相关的剂量差异。对于许多远距离治疗设备而言，这些差异的根源在于所采用的表格化百分深度剂量和组织空气比数值并不适用。通过针对多种深度和射野大小进行一系列深度处剂量测定，可获得合适的百分深度剂量和组织空气比。当采用合适的数值时，在所研究的所有剂量测定方法之间可发现极佳的一致性。
