Kanai Tatsuaki, Fukumura Akifumi, Kusano Yohsuke, Shimbo Munefumi, Nishio Teiji
National Institute of Radiological Sciences, 9-1, Anagawa 4-chome, Inage-ku, Chiba-shi, 263-8555 Chiba, Japan.
Phys Med Biol. 2004 Mar 7;49(5):771-81. doi: 10.1088/0031-9155/49/5/008.
The calibration coefficients of a parallel plate ionization chamber are examined by comparing the coefficients obtained through three methods: a calculation from a 60Co calibration coefficient, N(D, omega, 60Co), a cross-calibration of a parallel plate ionization chamber using a cylindrical ionization chamber at the plateau region of a mono-energetic beam and a cross-calibration of the chamber using a cylindrical chamber at the middle of the SOBP of the therapeutic beams. This paper also examines reference conditions for determining absorbed dose to water in the cases of therapeutic carbon and proton beams. In the dose calibration procedure recommended by IAEA, irradiation fields should be larger than 10 cm in diameter and the water phantom should extend by at least 5 cm beyond each side of the field. These recommendations are experimentally verified for proton and carbon beams. For proton beams, the calibration coefficients obtained by these three methods approximately agreed. For carbon beams, the calibration coefficients obtained by the second method were about 1.0% larger than those obtained by the third method, and the calibration coefficients obtained by cross-calibration using 290 MeV/u beams were 0.5% lower than those obtained using 400 MeV/u beams. The calibration coefficient obtained by the first method agreed roughly with the results obtained by SOBP beams.
通过比较三种方法获得的系数，来检验平行板电离室的校准系数：从钴 - 60校准系数N(D, ω, 60Co)进行计算、在单能束的坪区使用圆柱形电离室对平行板电离室进行交叉校准以及在治疗束的扩展布拉格峰（SOBP）中部使用圆柱形电离室对该室进行交叉校准。本文还研究了在治疗碳束和质子束情况下确定水中吸收剂量的参考条件。在国际原子能机构（IAEA）推荐的剂量校准程序中，照射野直径应大于10 cm，水模体应在野的每一侧至少向外延伸5 cm。这些建议已针对质子束和碳束进行了实验验证。对于质子束，通过这三种方法获得的校准系数大致一致。对于碳束，第二种方法获得的校准系数比第三种方法获得的大约大1.0%，使用290 MeV/u束进行交叉校准获得的校准系数比使用400 MeV/u束获得的低0.5%。第一种方法获得的校准系数与SOBP束获得的结果大致相符。
