Evaluation of Dosimetric Properties of Handmade Bolus for Megavoltage Electron and Photon Radiation Therapy

Abstract

Background: The use of boluses for radiation therapy is very necessary to overcome the problem of sending inhomogeneous doses in the target volume due to irregularities on the surface of the skin. The bolus materials for radiation therapy need to be evaluated. Objective:The present study aims to evaluate some handmade boluses for megavoltage electron and photon radiation therapy. Several dosimetric properties of the synthesized boluses, including relative electron density (RED), transmission factor, mass attenuation coefficient, percentage depth dose (PDD), and percentage surface dose (PSD) were investigated. Material and Methods:In this experimental study, we evaluated natural rubber, silicone rubber mixed either with aluminum or bismuth, paraffin wax, red plasticine, and play-doh as soft tissue equivalent. CT-simulator, in combination with ECLIPSE software, was used to determine bolus density. Meanwhile, Linear Accelerator (Linac) Clinac iX (Varian Medical Systems, Palo Alto), solid water phantom, and Farmer ionization chamber were used to measure and analyze of dosimetric properties. Results:The RED result analysis has proven that all synthesized boluses are equivalent to the density of soft tissue such as fat, breast, lung, and liver. The dosimetric evaluation also shows that all synthesized boluses have a density similar to the density of water and can increase the surface dose with a value ranging from 6-20% for electron energy and 30-50% for photon energy. Conclusion:In general, all synthesized boluses have an excellent opportunity to be used as an alternative tissue substitute in the surface area of the body when using megavoltage electron and photon energy.

Comparison of Absorbed Dose in Plasticine Bolus and Silicone Rubber Bolus

“…Plasticine itself is a compound made from mixing water, dyes, surfactants, lubricants, salts, starch-based binders, humectants, fragrances, and retrogradation inhibitors (Plurality, 2020). In the plasticine bolus, the relative electron density value was found to be equivalent to chest tissue to muscle, where the density value for chest tissue to muscle started from 0.976 cm/g3 to 1.043 cm/g3 (Endarko et al, 2020).…”

“…The constituent elements of siloxane inorganic polymeric bonds consist of silicon (Si), oxygen (O) atoms, and methyl bonds consisting of hydrogen (H) and carbon (C) atoms (Segura and Burillo, 2013). In the silicone rubber bolus, the relative electron density value was found to be equivalent to muscle tissue to bone, where the density value for muscle tissue to bone starts from 1.043 cm/g3 to 1.512 cm/g3 (Endarko et al, 2020).…”

“…Where, the sample dose is the dose when using a bolus, and the Open Field dose is the dose without a bolus (Endarko et al, 2020).…”

“…, where the depth for this 9 MeV energy is 2.1 cm. In theory, the thicker the bolus used, the lower the transmission factor value, if the transmission factor value is below 100%, the bolus can be said to be an absorbent material (Endarko et al, 2020).…”

“…The bolus used should have several characteristics including good elasticity, the absence of air bubbles on the surface of the bolus, when radiation is irradiated, it does not change shape and is also non-toxic. At this time, research on bolus materials continues to be developed using various materials such as natural rubber, superflab, plasticine, playdoh, paraffin wax, and silicone rubber (Endarko et al, 2020;Aras et al, 2020;Carina et al, 2020). The most commonly used bolus is a bolus made of plasticine, but this bolus has a rigid structure that can cause an air gap and is difficult to return to its original shape if pressed (Junaedi et al, 2016).…”