4.4 Measurement of %dd(10,10)x

Similar to the determination of TPR20,10(10) from measurements of TPR20,10(S), the %dd(10,10)x can be determined from the %dd(10) for S cm � S cm msr field size using the analytic relation provided by Palmans [90]. Figure 15 illustrates the experimental setup for the measurement of %dd(10, S) for S cm � S cm beam size and measurement depths of maximum dose (zmax) and 10 g/cm<sup>2</sup> at a source-to-surface distance of 100 cm.

Lead foil is not required in the measurements of %dd(10,S) for WFF radiation beams (below 10 MV). However, the use of lead foil of 1 mm thickness is recommended for %dd(10,S) measurements in FFF radiation beams; in order to remove the electron contamination and analytic expression, Eq. (27) is used to calculate %dd(10,10)Pb. Then %dd(10,10)x can be obtained from %dd(10,10)Pb using the relation provided by AAPM Task Group report 21.

The %dd(10,10)x can be calculated using the following expression:

$$\% \, dd(10, 10) \, = \frac{\% \, dd(10, \mathbb{S}) + \\$0c(10 - \mathbb{S})}{1 + c(10 - \mathbb{S})} \tag{27}$$

where 4 cm <sup>≤</sup> <sup>S</sup> <sup>≤</sup> 12 cm and C = (53.4 <sup>∓</sup> 1.1) � <sup>10</sup>�<sup>3</sup> .

## 5. Determination of absorbed dose

In case of radiation-emitting equipment, where field beam of 10 cm � 10 cm (fref) can be established, the dose measurement is performed using the

TPR20,10(10) for 10 cm � 10 cm can be derived using the following relationship:

Dependence of TPR20,10(S) on the field size S, for beam size ranging between 4 and 12 cm and photon energies

Theory, Application, and Implementation of Monte Carlo Method in Science and Technology

The experimental set-up to be used for measurement of TPR20,10(S).

Figure 14.

62

Figure 13.

between 4 and 10 MV.

This relation is valid when 4 cm <sup>≤</sup> <sup>S</sup> <sup>≤</sup> 12 cm, where C = (16.15 <sup>∓</sup> 0.12) � <sup>10</sup>�<sup>3</sup>

ð26Þ

.

recommendation provided by task group series (TRS) 398 and other equivalent protocols [1–7]. However, in radiation equipment where fref setting is not feasible, fmsr is used. The full width at half maximum of fmsr must satisfy small-field condition.

$$F\text{WHM} \ge \text{ } 2\,\, r\_{LCPE} + \,\, d\tag{28}$$

where is the detector reading for fmsr reworked for influential quan-

tities, is the detector calibration factor in terms of absorbed dose to water in fref beam and Q0 quality of beam, is the correction factor for difference in detector response of detector in beam quality Q0 in field size fref and response of detector in beam quality Q in fref beam size, and is the beam quality correction factor to account for the difference between the response of detector in beam quality Q, fref beam size and beam quality Qmsr, and beam size of fmsr.

Prospective Monte Carlo Simulation for Choosing High Efficient Detectors for Small-Field…

In order to determine the dose deposited in water for FFF radiation beam, the

where is the correction for beam quality for difference in response of the detector in beam QWFF, beam size fref and response of detector in quality of beam Q0, and beam size of fref. It can be taken from the international dosimetry protocols [1, 2, 7], and is the factor of correction for variation in response of the detector in the FFF and WFF radiation fields. It can be obtained from Monte Carlo studies. Figure 16 summarizes the different conditions

Schematic summary of the determination of absorbed dose in case of small beams considering the case of machine specific reference field according to the formalism given by TRS 483. The arrows and formulas labeled

(1), (2) and (3) refer to Section 6.1.1, 6.1.2 and 6.1.3, respectively.

discussed above for the determination of dose deposited in water.

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following relation can be used:

DOI: http://dx.doi.org/10.5772/intechopen.89150

Figure 16.

65

## 5.1 Measurement of absorbed dose in fmsr
