## 4 Discussion  
The \(D_{w}\) measurements using the three dosimetry codes of practice showed comparable results. Minor discrepancies in measured absorbed doses arose from the characteristics of the photon beam used, the ionization chamber used, and the measurements of the influence quantities [6]. Two things correct chamber readings: perturbation factors that correct deviations from Bragg-Gray behavior and influence quantities that correct for nonreference conditions, including \(k_{pol}\), \(ks\), and \(k_{TP}\) correction factors. Different components of the perturbation factors included in the beam quality correction factors influenced the uncertainties. Although the two protocols use different beam quality specifics, the differences in absorbed dose measurements using \(TPR_{20,10}\) and \(\%dd\) (\(10\))\(x\) are small--about 0.5% for external beam radiotherapy and \(\leq\)1% for calibrations in primary and other standard laboratories [17]. Thus, the effect of different beam quality indexes is small compared with the overall uncertainties [6; 17]. Our results emulated previous studies, which reported discrepancies in absorbed dose measurements among the three protocols that varied from 0.23% to 0.7% [9; 17; 18]. The results were ascribed to the differences in methods used for beam quality determination and measurements of chamber influence parameters. Figure 2 presents ratios of the measured \(D_{w}\) obtained with three dosimetry protocols, (a) AAPM TG-51/IAEA TRS-398, (b) IAEA TRS-398/DIN 6800-2, and (c) AAPM TG-51/DIN 6800-2. The obtained chamber-to-chamber variation was 0.09% in TRS-398/TG-51, 0.03% in TRS-398/DIN, and 0.02% in TG-51/DIN 6800-2. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Chamber**} & \multicolumn{3}{c}{**6 MV**} & \multicolumn{3}{c}{**20 MV**} & \multicolumn{3}{c}{**4 MV**} & \multicolumn{3}{c}{**10 MV**} \\ \cline{2-13}  & **TRS** & **TG-51** & **DIN** & **TRS** & **TG-51** & **DIN** & **TRS** & **TG-51** & **DIN** & **TRS** & **TG-51** & **DIN** \\ \hline \multicolumn{13}{c}{\(k_{pol}\)} \\ NACP & 0.9981 & 0.9981 & 0.9982 & 0.999 & 0.999 & 0.999 & 0.999 & 0.9971 & 0.999 & 0.9978 & 0.9978 & 0.9978 \\ CC15 & 0.9994 & 0.9995 & 0.9994 & 0.9994 & 0.9995 & 0.9994 & 0.9988 & 1.0002 & 0.9988 & 0.9998 & 0.9998 & 0.9998 \\ FC65-G & 0.9989 & 0.9987 & 0.9989 & 0.9989 & 0.9989 & 0.9989 & 0.9989 & 0.9989 & 0.9989 & 0.9989 & 0.9989 \\ \multicolumn{13}{c}{\(k_{\rm T}\)} \\ NACP & 1.0062 & 1.0062 & 1.0033 & 1.0071 & 1.0073 & 1.0045 & 1.0036 & 1.0032 & 1.0028 & 1.0026 & 1.0027 & 1.0023 \\ CC15 & 1.0043 & 1.0043 & 1.0031 & 1.0043 & 1.0043 & 1.0031 & 1.0026 & 1.0017 & 1.0023 & 1.0027 & 1.0028 & 1.0023 \\ FC65-G & 1.0025 & 1.0027 & 1.0022 & 1.0033 & 1.0035 & 1.0027 & 1.0025 & 1.0027 & 1.0022 & 1.0033 & 1.0035 & 1.0027 \\ \multicolumn{13}{c}{\(k_{\rm T}\)} \\ NACP & 1.0041 & 1.0041 & 0.9973 & 1.0041 & 0.9973 & 1.0041 & 1.0127 & 1.0058 & 1.0127 & 1.0127 & 1.0058 & 1.0127 \\ CC15 & 1.0135 & 1.0066 & 1.0135 & 1.0135 & 1.0066 & 1.0135 & 1.0128 & 1.006 & 1.0128 & 1.0128 & 1.006 & 1.0128 \\ FC65-G & 1.0130 & 1.0061 & 1.013 & 1.013 & 1.0061 & 1.0130 & 1.0061 & 1.0130 & 1.0130 & 1.0061 & 1.0130 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Correction factors for the polarity effect (\(kpol\)), ion recombination (\(ks\)), and temperature and pressure correction factors (\(k_{TP}\)). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**MV** & **Ionization Chamber** & **TRS-398/ TG-51** & **TRS-398/DIN 6800-2** & **TG-51/DIN 6800-2** \\ \hline \multirow{4}{*}{4} & FC65-G & 0.9999 & 1.0010 & 1.0011 \\  & CC15 & 1.0022 & 1.0012 & 0.9990 \\  & NACP-02 & 1.0021 & 1.0011 & 0.9990 \\  & FC65-G & 1.0177 & 1.0051 & 0.9935 \\
6 & CC15 & 1.0104 & 1.0033 & 0.9930 \\  & NACP-02 & 1.0098 & 1.0050 & 0.9952 \\  & FC65-G & 1.0077 & 1.0039 & 0.9962 \\
10 & CC15 & 1.0086 & 1.0044 & 0.9958 \\  & NACP-02 & 1.0077 & 1.0047 & 0.9970 \\  & FC65-G & 1.0103 & 1.0088 & 0.9985 \\
20 & CC15 & 1.0079 & 1.0079 The cylindrical chambers demonstrated a chamber-to-chamber dose variation of 0.09%.