Determination of non-uniformity correction factors for cylindrical ionization chambers close to ¹⁹²Ir brachytherapy sources

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• 作者：Tö ; lli ; H. ; Bielajew ; A. F. ; Mattsson ; O. ; Sernbo ; G.
• 刊名：Radiotherapy and Oncology
• 出版年：1995
• 出版时间：October, 1995
• 年：1995
• 卷：37
• 期：Complete
• 页码：S10
• 全文大小：103 K

文摘

When ionization chambers are used in brachytherapy dosimetry, the measurements must be corrected for the non-uniformity of the incident photon fluence. The theory for determination of non-uniformity correction factors, developed by Kondo and Randolph (Rad. Res. 1960) assumes that the electron fluence within the air cavity is isotropic and does not take into account material differences in the chamber wall. The theory was extended by Bielajew (PMB 1990) using an anisotropic electron angular fluence in the cavity. In contrast to the theory by Kondo and Randolph, the anisotropic theory predicts a wall material dependence in the non-uniformity correction factors. This work presents experimental determination of non-uniformity correction factors at distances between 10 and 140 mm from an Ir-192 source. The experimental work makes use of a PTW23331-chamber and Farmer-type chambers (NE2571 and NE2581) with different materials in the walls. The results of the experiments agree well with the anisotropic theory. Due to the geometrical shape of the NE-type chambers, it is shown that the full length of the these chambers, 24.1mm, is not an appropriate input parameter when theoretical non-uniformity correction factors are evaluated.