*3.1. Density Measurement of DSF-Based R. spp. Particleboard Phantoms*

Figure 4 displays the variation of average densities with point distribution of DSFbased *R.* spp. composite particleboard phantom slabs. It is seen that the constructed particleboard phantoms exhibit acceptable quality values of average densities to those of water (1.00 gcm<sup>−</sup>3) and solid water phantom (1.04 gcm−3) in the range between 0.99 ± 0.01 –1.04 ± 0.03 gcm−3, making them potentially suitable for use in the fabrication of tissueequivalent phantom materials. This is attributed to better adhesive-coated particles that provide intimate contact with the mat's wood particles and, thus, increase the bonding capabilities of the particleboards. This revealed that the combination of DSF/NaOH/IA-PAE with an increased percentage concentration of IA-PAE up to 15 wt% leads to an improvement in the average mass density of the particleboards approaching the value of water. These findings are in good agreement with previous studies of the average density of particleboard phantoms for dosimetric applications at high photon and electron energies utilized in radiation therapy [5,10].

**Figure 4.** Average density with point distributions of DSF/NaOH/IA-PAE/*R.* spp. composite particleboard phantoms.

### *3.2. Evaluation of RAPs*

The experimental computation has been performed in order to obtain the total LAC and MAC values for photon energies of 0.662 and 1.250 MeV and compared with those of

solid water phantom and theoretical values of water using cross-section data (XCOM), as displayed in Table 4. The errors in density, thickness, incident, and transmitted gamma-ray intensities were used to evaluate the uncertainties in experimental MAC. The dependency of MAC values on photon energies can be explained by the dominance of partial photon interactions (e.g., photoelectric absorption, coherent scattering, incoherent scattering, and pair production) with the samples. As we know, the photoelectric effect dominates below, and pair production dominates above 1 MeV, whilst Compton scattering dominates at around 1 MeV [8,33]. The calculated values of LAC ranged from 0.059–0.083 cm−<sup>1</sup> for 0.662 MeV photon energy, while for 1.250 MeV, the observed LAC values were within 0.043–0.056 cm−1. Additionally, the observed total MAC values for these photon energies ranged between 0.059–0.082 cm2g−<sup>1</sup> at 0.662 MeV, whereas for 1.250 MeV, the MAC values were found to range between 0.041–0.056 cm2g−1. The estimated errors in experimental total MAC values for all the samples were less than 0.028%. As observed from Figure 5a, the difference of total MAC values with the incident photon energy for all composite particleboard samples and those of solid water phantom and water (XCOM) is almost identical as IA-PAE concentration increases with A15, depicting higher MAC values for both photon energies, potentially providing a useful approximation of tissue-equivalent phantom materials. As expected, by increasing the incident photon energy, the total MAC values in all samples decreased slightly. This behavior may be due to the incoherent scattering process, which becomes the dominant mechanism in this region [34]. This can be ascribed to the fact that the Compton scattering cross-section is inversely proportional to the incoming photon energy (E−1) and varies linearly with atomic number. In all the investigated samples, by increasing the incident photon energy, the highest HVL and MFP values were found for samples containing A0 and A5, while the lowest values were found for water (XCOM) and solid water phantom (Figure 5b,c). It was also observed that, in all samples and for all energies, A15 has the lowest HVL and MFP values with approximately no noticeable difference relative to those of solid water phantom and water (XCOM), which implies a higher radiation absorption ability. A comparison between the calculated values shows reasonable agreement with 15 wt% IA-PAE, solid water phantom, and theoretical values of water (XCOM), as depicted by the *χ*<sup>2</sup> values (Table 5). It can be seen that, among the selected samples, A15 provided the least values of *χ*<sup>2</sup> (0.044). This revealed, with an insignificant difference, the closest value of RAPs to those of solid water phantom and the theoretical value for water (XCOM).


**Table 4.** LAC and MAC values of DSF/NaOH/IA-PAE/*R.* spp. particleboards and solid water phantoms in comparison with water (XCOM).

**Figure 5.** RAPs of DSF-based composite phantoms, water (XCOM), and solid water phantom against gamma energies: (**a**) MAC, (**b**) HVL, and (**c**) MFP.

**Table 5.** *χ*<sup>2</sup> values for MAC of DSF-based *R.* spp. particleboards and solid water phantoms.


*3.3. Dosimetric Characteristics of DSF-Based R. spp. Particleboard Phantoms*

3.3.1. Measurement of Photon Beam Quality Index

The tissue-phantom ratio (TPR20,10) remains the most appropriate parameter for ascertaining the beam quality of a clinical photon beam. It is believed that material with near TPR20,10 to water has similar RAPs to those of water and soft tissue [35]. The measured TPR20,10 values of DSF-based *R.* spp. particleboards (sample A15), solid water, and water phantoms for 6 and 10 MV photon beams with the use of IC are presented in Tables 6 and 7. The result indicates that the percentage discrepancies of sample A15 in comparison to those of solid water and water phantoms are in the range between 0.29–0.72% for 6 MV photons. Likewise, the discrepancies for the 10 MV photon beam are within the acceptable range of 0.26–0.65%. These results are in good agreement with previous work on the TPR20,10 of renewable resources in the respective photon energy ranges [5,10].


**Table 6.** TPR20,10 measurement for DSF/NaOH/IA-PAE/*R.* spp. particleboards (sample A15), water, and solid water phantoms for 6 MV photons.

Note: W, S, and *R* depict the water, solid water, and DSF-based (DSF/NaOH/IA-PAE/*R.* spp.) phantoms.

**Table 7.** TPR20,10 evaluation for DSF/NaOH/IA-PAE/*R.* spp. particleboards (sample A15), water, and solid water phantoms for 10 MV photons.


Sample A15 with *p*-values of 0.071 and 0.069 for 6 and 10 MV photons showed no significant difference to those of water and solid water phantoms in the photon beam radiation quality, as presented in Tables 8 and 9. These findings demonstrated that DSF/NaOH-based *R.* spp. particleboard phantoms with 15 wt% IA-PAE (sample A15) provide the ascribable characteristics that are proper as appropriate tissue-equivalent phantom materials.

**Table 8.** Paired *t*-test of the TPR20,10 measurement for 6 MV photons.


**Table 9.** Paired *t*-test of the TPR20,10 measurement for 10 MV photons.


#### 3.3.2. Determination of PDD Photon Beams Using IC

The measured PDD values of 6 and 10 MV photon beams with the use of IC for sample A15, water, and solid water phantoms are shown in Figure 6. The computed profiles were normalized to the maximum dose in the depth-dose profile positioned symmetrically opposite the IC within the photon beam to ensure that the profiles being compared were identical to those of water and solid water phantoms. The dose first increases steadily below the surface dose (*ds*), reaches a maximum value (*dmax*) at *zmax*, then decreases almost gradually until it reaches *dext* at the patient's exit position. The discrepancies in the d\_max in comparison to those of water and solid water phantoms were at most 1.08% and 1.28% for 6 MV photons (Figure 6a). On the other hand, for 10 MV photons (Figure 6b), the observed percentage differences in the *dmax* were found to be 5.42% and 6.70% at the dose build-up region, which is the region from the phantom surface to the depth at d\_max and the equilibrium region. The greatest difference was recorded for 10 MV photons for all the phantoms, which is similar to previous observations by Yusof et al. [5] and Banjade et al. [10]. The observed values of the surface dose were found to range between 2.29% and 2.34% for 6 MV photons. Similarly, the surface dose values for 10 MV photons were found to be 4.69% and 5.29%, respectively. The PDD values for the examined particleboard phantoms at a depth beyond *dmax* indicates no significant difference with percentage difference within the limit of 0.09–0.16% for 6 MV, while for 10 MV photon, the variations in the depth beyond *dmax* were found to range between 0.37–0.70%, which is consistent with those of water and solid water phantoms.

**Figure 6.** PDD curves for water, solid water, and DSF/NaOH/IA-PAE/*R.* spp. particleboard phantoms using IC for: (**a**) 6 MV and (**b**) 10 MV photons.

#### 3.3.3. PDD Curves for Gafchromic EBT3 Radiochromic Films for Photon Beams

Figure 7 shows a comparison between the estimated PDD profiles for sample A15, water, and solid water phantoms for 6 MV and 10 MV photon beams using Gafchromic EBT3 radiochromic films. As shown in the Figures, the percentage variations in the *dmax* of the particleboard phantom, relative to those of water and solid water phantoms, were found to be 1.03% and 1.68% for 6 MV photons (Figure 7a), whereas the contrast between the measured PDD at all depths for 10 MV photon beams indicates good consistency with a difference within the range of 5.42% and 5.92% (Figure 7b). Overall, the results depict agreement with those of water and solid water phantoms in the build-up region for 6 MV photons with lower variations in the PDD values at *dmax*, whereas the variations were marginally higher for 10 MV photons with discrepancies found within 5% and 7%. This can be ascribed to the fact that the dominant free electron population originating in the buildup region continues to cause further interactions as a result of pair production, Compton scattering, and the photoelectric effect. High energy electrons are emitted as high energy photons (10 MV) interact with the phantoms and are absorbed by their interaction with

the phantom. The resulting electrons will reduce with depth inside the phantoms owing to the continuously reduced energy fluence of the photons. The corresponding results for the surface dose of fabricated particleboards with water and solid water phantoms were found to be within 2.23–2.44% and 4.48–4.84%. With regards to the depth beyond *dmax*, the PDD values showed agreement to those of water and solid water phantoms, with percentage deviation in the interval of 0.01–0.02% and 0.06–0.07%, respectively. These trends are similar to what was reported for IC performance.

**Figure 7.** PDD plots with the use of EBT3 film for water, solid water, and DSF/NaOH/IA-PAE/*R.* spp. particleboard phantoms ascertained for: (**a**) 6 MV and (**b**) 10 MV photons.
