Enhancing Radiotherapy Bolus Characteristics through Comparative Analysis of Added Sawdust and Bagasse Powder: A Comprehensive Study of Physical and Mechanical Properties

Research has been successfully conducted on the manufacture of synthetic bolus for radiotherapy made of silicone rubber containing polydimethyl siloxane and alginate as well as the addition of bagasse and wood sawdust. The purpose of this study was to determine the characterization of radiotherapy bolus by analyzing the comparison of the addition of bagasse and wood sawdust through its physical and mechanical properties. The methods used in this research are bolus sample preparation, characterizations of physical and mechanical properties and analysis of characterizations results. From the physical properties, the results of the characterizations of this research obtained that in the density test the bolus synthesis with the addition of bagasse at a thickness of 1.5 cm and 2 cm was 0.6 g/cm3 and 0.55 g/cm3 respectively, while the bolus synthesis with the addition of wood sawdust at a thickness of 1.5 cm and 2 cm had a density of 0.86 g/cm3 and 0.75 g/cm3 respectively. In porosity testing, the 1.5 cm thick synthetic bolus with the addition of bagasse and wood sawdust has a porosity of 6.6% while the bolus with a thickness of 2 cm in the addition of bagasse and wood sawdust has a porosity of 5%. In the water absorption test, the synthetic bolus in the addition of bagasse with a thickness of 1.5 cm and 2 cm has a water absorption of 11.11% and 9.09%, respectively. Bolus synthesis with the addition of wood sawdust with a thickness of 1.5 cm and 2 cm had a water absorption of 7.69% and 6.66%, respectively. From the mechanical properties, tensile strength testing of the synthesized bolus of 1.5 cm and 2 cm thickness with the addition of bagasse has a tensile strength value of 0.56 MPa and 0.38 MPa, respectively. while the tensile strength of the synthesized bolus with the addition of wood sawdust of 1.5 cm and 2 cm thickness is 0.42 MPa and 0.33 MPa, respectively. In the elongation at break test, the synthesis bolus with the addition of bagasse at a thickness of 1.5 cm and 2 cm was 92.33%, 52.69% respectively and the bolus with the addition of wood sawdust at a thickness of 1.5 cm and 2 cm had a large elongation at break of 93.49% and 106%. And in the elastic modulus test, the synthesis bolus in the addition of bagasse with a thickness of 1.5 cm and 2 cm is 0.611 MPa and 0.723 MPa respectively while the elastic modulus in the synthesis bolus with the addition of wood sawdust with a thickness of 1.5 cm and 2 cm is 0.465 MPa and 0.319 MPa respectively. From the physical and mechanical tests that have been carried out, the synthetic bolus with the addition of bagasse and wood sawdust at a thickness of 1.5 cm given the codes A1 and B1 can be said to have good material and has high elasticity compared to the synthetic bolus with a thickness of 2 cm both from the addition of bagasse and wood sawdust given the codes A2 and B2.


Introduction
Radiotherapy is an alternative method of treating cancer that utilizes ionizing radiation [1].One of the emitters of ionizing radiation is the Linear Accelerator (Linac), which produces high-energy photons and electrons used for cancer treatment [2].The compensation network used in photon and electron therapy is called a bolus [3].Bolus is a soft and rigid material with properties equivalent to human body tissue.Boluses are applied to the skin surface to increase the surface dose, decrease the depth dose, and even out uneven tissue.In addition, boluses reduce skin tissue damage in the area around the cancer, reduce radiation penetration, and provide an even dose distribution on uneven surfaces [4].So that the bolus has the potential to be developed into a medical product for therapeutic applications.Radiotherapy is a method of treating cancer that utilizes radiation treatment.The percentage of dose on the skin's surface is not 100%; the maximum dose is obtained only at a certain depth; therefore, efforts are needed so that the cancer tissue reaches the maximum dose while the surrounding normal tissue gets the minimum dose.The optimum dose in cancer can be obtained by planning and using the right technique.So, the use of a bolus is one of the techniques commonly used in radiotherapy.Therefore, efforts are needed in such a way that the cancer tissue reach the maximum dose while the surrounding normal tissue Acquiring the minimum dose.Materials that are often used as a bolus are wax (paraffin wax), polystyrene, leucite, super stuff and super flab, while super flab is the best because it is transparent, flexible and water-like (water equivalent) [5].The medical bolus materials that have been used as research are boluses made of aquaplast, elastic-gel, rayon fabric, polydimethyl siloxane, natural rubber [6].An alternative material that can be used in bolus production are silicone rubber (SR) and alginate [7].The preference for sawdust and bagasse as bolus fillers is because sawdust and bagasse contain cellulose, hemicellulose and lignin and when combined with polydimethyl siloxane and alginate can absorb the dose of ionizing radiation fired to the body surface.Alginate is a group of polysaccharides extracted from brown seaweed [8].Alginate is a hydrocolloid which is widely used as a thickener, gelling agent, stabilizer and emulsifier [9].In this study, the authors hope that the manufacture of medical bolus from bagasse powder and wood sawdust has good material strength in terms of elasticity and lasts for a long period of time besides in the process of making this bolus relatively quickly formed compared to other studies that are less elastic.

Materials and Methods
The materials used are alginate, silicone rubber (SR) RTV 52 which contains polydimethyl siloxane as a matrix in the manufacture of radiotherapy boluses, bluesil 60R catalyst as an ingredient to accelerate the hardening of radiotherapy boluses, alginate as an adhesive in the manufacture of radiotherapy boluses, wood sawdust and bagasse.The manufacture of radiotherapy bolus in this research is made from silicone rubber RTV 52, alginate and wood sawdust and bagasse.In addition to these basic materials, Catalyst bluesil 60R catalyst is also needed to accelerate the hardening process of the radiotherapy bolus.All materials were weighed with variations in composition ratio which can be seen in Table 1  The first step is sawdust and bagasse were soaked with distilled water for 2 x 24 hours.Then the sawdust and bagasse were dried in an oven at 80ºC for 24 hours to remove the water content.Then, they were ground with a ball mill for 2 hours at a speed of 250 rpm and then filtered using a sieve measuring 200 mesh or 0.074 mm so that the result sawdust and bagasse powder.Each of the materials that make up the radiotherapy bolus, namely silicon rubber, alginate, catalyst, was weigh with the composition that has been shown in the table 1. Mixed in the bowl and mixed to mix the mixture evenly using a mixer at room temperature for 5 minutes until the mixture became homogeneous and there was no agglomeration.Then it poured into the acrylic glass mold.Then poured into an acrylic glass mold measuring (11 x 11 x 1) cm 3 with each bolus thickness composition of 1.5 cm and 2.0 cm.The last step is that the bolus sample is dried in an oven at 25 o C for 2 days.After the samples were formed, characterization was made to test the physical and mechanical properties of the bolus.Physical properties testing includes testing density, porosity and water absorption in the bolus.Furthermore, the mechanical properties tested consisted of tensile strength, elongation at break and modulus of elasticity.

Results And Discussion
With remark ρ is density (g/cm 3 ); m is mass (g); and v is volume of sample (cm 3 ).
The results of radiotherapy bolus density testing that have been obtained can be seen in the figure below: Figure 1 shows the density value of the synthesized bolus in various compositions with the addition of sawdust and bagasse.The density of the addition of bagasse in sample codes A1 and A2 has a density of 0.6 g/cm 3 and 0.55 g/cm 3 , respectively.In sample codes B1 and B2, the addition of sawdust increased the density.The density values are 0.86 g/cm 3 and 0.75 g/cm 3 , respectively.The increase in the density value of wood sawdust is because the composition of sawdust is easily bound well by rubber silicate and alginate and easily forms homogeneity so that the synthesized bolus is denser than using bagasse powder.

Porosity testing
Porosity is the number of pores in a material that is calculated by finding the percentage (%) based on the absorbency of the material to water and water by finding the percentage (%) based on the material's absorption of water and ratio of the volume absorbed to the total volume of the sample.For calculate porosity with reference to ASTM C 20 -00, using equation ( 2) mb is the wet mass of the sample (g), mk is the dry mass of the sample (g), ρwater is the density of water (g/cm 3 ) and V is the total volume of the sample (cm 3 ).

Figure 2. Porosity of synthesized bolus
Figure 2 shows the porosity of synthesized bolus.The porosity of bagasse and sawdust with a thickness of 1.5 cm each A1 and B1 was obtained at 6.6% and the porosity of sawdust and bagasse with a thickness of 2 cm each A2 and B2 obtained a porosity of 5%.Bolus made from silicon rubber and alginate in each variation of the composition of the synthesized bolus has a higher porosity value of 17.12%.Tampubolon et al. 2019, When compared to the results of the porosity percentage in this study, it looks lower.This is because the air bubbles contained in the bolus synthesized with silicone rubber and alginate in mixing wood sawdust and bagasse are less homogeneous so that they can fill the void in the synthesized bolus.

Water absorption testing
Water absorption is the ability of a material to absorb water, where water absorption is directly proportional to the number of pores of a material.The test is based on ASTM C 20 -00.The equation (3) for calculating the water absorption of a material is: ݉݇ DSA is the water absorption (%), mb is the wet mass of the sample (g), mk is the dry mass of the sample (g).The water absorption obtained in this study is shown in the figure below: 6.6% 6.6% 7.0%  Figure 3 shows the value of water absorption of the material synthesized bolus.The value of water absorption of the bagasse thickness at 1.5 cm (A1) and thickness 2 cm (A2) respectively the value is 11.11% and 9.09 %.The value of water absorption of the wood sawdust thickness at 1.5 cm (B1) and thickness 2 cm (B2) respectively are 7.69% and 6.66 %.From the graph above, it can be concluded that the water absorption value of bagasse powder is higher than that of wood sawdust.

Mechanical Testing of Radiotherapy Bolus
In testing the mechanical properties there are tests of tensile strength, modulus of elasticity, and elongation at break shown at table 2 using equation ( 4): From eq (4) obtain modulus of elasticity at equation ( 5): (5) to determine the elongation at break, it is determined from the % Elongation at break using equation ( 6).
( Where ߝ is the strain, ‫0ܫ‬ is the length of the specimen initially (m), and ‫݂ܫ‬ is the length of the specimen after being loaded (m).

Table 2. Mechanical Properties Test
Table 2 is the result of calculations from mechanical testing, namely the stress and strain equations on the synthesis bolus.Mechanical testing was conducted to determine the effect of bagasse and wood sawdust on the mixture of silicone rubber and alginate.Mechanical properties include tensile strength, elongation and modulus of elasticity.Figure 4 (a) shows the tensile strength test values for the bolus material with the addition of bagasse A1 and A2 are 0.56 MPa and 0.38 MPa.While the results of tensile strength on the addition of wood sawdust B1 and B2 are 0.42 MPa and 0.33 MPa. Figure 4(b) shows the results of the percentage of elongation in each synthetic bolus added with bagasse A1 and A2 which are 92.33% and 52.69% respectively while the results of the percentage of elongation value of the synthetic bolus added with wood sawdust B1 and B2 are 93.49% and 106% respectively.Figure 4(c) shows the results of the modulus of elasticity of the synthetic bolus added with bagasse A1 and A2 of 0.611 MPa and 0.723 MPa respectively, while the synthetic bolus added with wood sawdust B1 and B2 have a modulus of elasticity of 0.465 MPa and 0.319 MPa respectively.Based on the test results of mechanical properties including tensile strength, elongation at break and modulus of elasticity, it shows that the tensile strength of the synthetic bolus with a thickness of 1.5 cm is more optimum than the tensile strength of the synthetic bolus with a thickness of 2 cm either with the addition of bagasse or wood sawdust.When compared to the research of Sianturi, et al. (2019) [10] , the synthetic bolus with a thickness of 1.5 cm or 15 mm has a tensile strength value of 3.834 MPa and a young modulus of 0.8252 MPa without the addition of bagasse or wood sawdust.While the results of the percentage of elongation of bolus with a thickness of 1.5 cm or 15 mm in the research was 147.243% [9] .The difference in mechanical test results in the research of synthetic bolus added with bagasse and wood sawdust greatly decreased the results of tensile strength, elongation and modulus of elasticity with the addition of bagasse and wood sawdust.This can be due to the content of cellulose and lignin in bagasse and wood sawdust which are still agglomerated / piled up or not completely dissolved and the different thickness on each side of the synthesis bolus in this study.However, when viewed in general in the results of mechanical tests in this study that the more optimum synthesis bolus is the addition of bagasse with a thickness of 1.5 cm.The thicker the bolus at a thickness of 2 cm, the tensile strength and elongation decrease.However, the modulus of elasticity increases slightly.This shows that the content of cellulose and lignin in bagasse is more than wood sawdust.

Conclusion
In this research, radiotherapy bolus made from silicone rubber (SR) RTV 52 containing polydimethyl siloxane alginate, and catalyst with the addition of bagasse and wood sawdust with thickness of 1.5 cm and 2 cm has been conducted Physical Testing of Radiotherapy Bolus and Mechanical Testing of Radiotherapy Bolus.Physical testing includes density, porosity and water absorption tests for each bolus with a thickness of 1.5 cm and 2 cm with each addition of bagasse and wood sawdust.When viewed from the thickness of the synthetic bolus that has been made, namely 1.5 cm, it is still said to be better and has a high value compared to the thickness of the bolus of 2 cm.So, in physical testing, the bolus that is said to be good is a synthetic bolus with a thickness of 1.5 cm.Mechanical testing of the bolus includes tensile strength test, percentage elongation and elastic modulus test of each bolus with a thickness of 1.5 cm and 2 cm and each addition of bagasse and wood sawdust.Based on the results of the mechanical test, the bolus with a thickness of 1.5 cm in the addition of bagasse and wood sawdust is said to have good quality, except that it needs better stirring to avoid clumping so that the mechanical test results can have a better value.In general, from the results of this study, it can be concluded that boluses with codes A1 and B1 are still said to have good material strength and have high elasticity compared to boluses with codes A2 and B2.

Acknowledgments
The 3.1 Physical Testing of Radiotherapy Bolus 3.1.1Density testing Density testing was conducted to determine the density of the radiotherapy bolus material by measuring the mass per unit volume.Density test referring to ASTM 134-95 can be calculated by using equation (1): ρ= ௩

Figure 3 .
Figure 3. Water absorption of Bolus Synthesized

Figure 4 .
Mechanical Testing Results of Bolus synthesis added with bagasse and wood sawdust authors would thank Universitas Sumatera Utara of Talenta Research Skema Terapan of Contract Number 193/UN5.2.3.1/PPM/KP-TALENTA/2022date at 09 AGUSTUS 2022 and General Hospital Adam Malik of North Sumatra, Medan for contributing to providing facilities, science of radiology and technical support for the implementation of this research to be completed.