## 4 Discussion and Conclusions  
This work aimed to establish a protocol for measuring the dose in water delivered by small fields using TLD-100 micro-cubes. The results presented in this work can serve as the basis for such measurements and present a protocol for measuring the dose in water delivered by small fields (with diameters ranging from 4 to 20 mm), for a dose range between 0.5 to 3.0 Gy, using TLD-100 micro-cubes. The aspects to be highlighted and that must be taken Into account in this methodology are as follows:  
* It is necessary for the micro-TLDs of the dosimeters to undergo annealing for one hour at 400 \({}^{\circ}\)C and two hours at 100 \({}^{\circ}\)C.
* The use of radiochromic films is necessary for the audit in small photon beams to identify the position of the dosimeters during irradiation. * The use of five dosimeters is suggested, arranged as shown in Figure 1, for each irradiation in order to obtain the calibration curve and conduct the audit. * One face of the dosimeters should be marked so that the thermally stimulated face is always the same during the reading. * At the moment of reading, the nitrogen flow should be kept as low as possible in order to avoid movements of the dosimeter. * The sensitivity factor and the central dosimeter signal should be used to reduce the uncertainty. * The calibration curve of the square field size closest to the field to be studied should be used. By following this protocol, a considerable improvement in the reproducibility of the responses can be achieved, with a decrease in uncertainty of up to 7%--from 10 to 3%--when marking the dosimeters and using radiochromic dye film to determine the positions of the dosimeters in the center of the field. A pilot dosimetric audit was carried out using the proposed protocol over a linear accelerator using small circular collimator photon beams. The results shown in this work are in agreement with those reported in similar audits (as presented in Table 1). Some authors have reported differences of up to 22% between the measured and calculated doses, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Field Diameter (mm)** & **Measured Dose (Gy)** & **Percentage Difference (\%)** \\ \hline
20.0 & 1.97 \(\pm\) 3.6\% & 1.7 \\
17.5 & 1.95 \(\pm\) 3.6\% & 2.6 \\
15.0 & 2.06 \(\pm\) 1.5\% & 2.8 \\
12.5 & 2.06 \(\pm\) 1.5\% & 2.9 \\
10.0 & 2.05 \(\pm\) 1.5\% & 2.6 \\
7.5 & 1.96 \(\pm\) 1.5\% & 2.0 \\
6.0 & 2.04 \(\pm\) 1.5\% & 2.2 \\
4.0 & 1.96 \(\pm\) 1.5\% & 2.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: TLD-measured doses and the percentage difference relative to the prescribed dose. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Field Diameter (mm)** & **Field Output Factor** & **MU** & **Dose [Gy]** \\ \hline
20.0 & 0.883 \(\pm\) 0.002 & 227 & 2.004 \\
17.5 & 0.871 \(\pm\) 0.002 & 230 & 2.003 \\
15.0 & 0.856 \(\pm\) 0.003 & 234 & 2.003 \\
12.5 & 0.834 \(\pm\) 0.002 & 240 & 2.002 \\
10.0 & 0.784 \(\pm\) 0.002 & 255 & 1.999 \\
7.5 & 0.733 \(\pm\) 0.002 & 273 & 2.001 \\
6.0 & 0.677 \(\pm\) 0.002 & 295 & 1.997 \\
4.0 & 0.580 \(\pm\) 0.001 & 345 & 2.001 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Output factors for estimating the delivered dose and calculating the MU. while differences of 3% have been obtained with standard reference field sizes of 10 cm \(\times\) 10 cm [22; 23]. [PERSON] et al. [21] reported differences of up to 10% when analyzing cases of intensity-modulated fields. Finally, [PERSON] et al. [20] reported differences smaller than 5% for a 1 cm \(\times\) 1 cm field (the closest to the field sizes audited in this study) in 69% of the audited institutions, and lower than 2.9% in postal audit. In this work, the percentage difference between the delivered and measured doses was smaller than 3%, which is less than or equal to the differences reported in other works. The methodology used to audit small radiation fields proposed in this work was validated on the basis of the results obtained.