Fabrication of Alternative Bolus for Cobalt-60 Teletherapy Using Two Locally Available Materials

Abayomi Moses Olaosun,Caleb Ayoade Aborisade,Denen Eric Shian,Fatai Akintunde Balogun,Iyobosa Blessing Uwadiae

doi:10.11648/j.ep.20200401.13

Abstract

Bolus is a tissue equivalent material which is use in radiation therapy in order to eliminate skin sparing effect of higher energy photon beams that always reduce the surface dose. There are several commercially bolus material such as Superflab, Aquaplast and gels for use but literature have shown that they are expensive and are not readily available in developing countries. This work presents the fabrication of an alternative bolus for Cobalt-60 Teletherapy using two locally available materials (Beeswax and Petroleum jelly). Beeswax was liquefied at a temperature of 60°C followed by the addition of Petroleum jelly at ratio 3:1 by weight for proper molding and flexibility. In order to determine the depth of maximum dose, Thermoluminescent Dosimeter (TLD) chips were inserted in between ten bolus materials of thickness 0.5 cm that were arranged in layers and placed on a solid water phantom. This was then irradiated with Cobalt-60 radiation source using field size ranging from 5 cm x 5 cm to 10 cm x 10 cm field size. For all the field size, maximum absorbed dose was found to be at 0.5 cm depth. This depth of maximum dose was compared to two tissue equivalent materials in use in radiation therapy: water and Superflab for Cobalt-60 Teletherapy and found to be in agreement. The percentage dose deviation when compared with water for 1 cm, 2 cm, 3 cm, 4 cm and 5 cm were less than 2%. The flexibility of the bolus material and the analysis of the absorbed dose measured have shown that the fabricated bolus material of thickness 0.5 cm can be used as an alternative bolus material for Cobalt-60 Teletherapy.

Highlights

In radiation therapy, the use of megavoltage photon beams usually exhibit skin sparing effect
Skin sparing effect is a major challenge for superficial tumours because it always causes the dose at the skin surface to be lower when compared to the maximum dose at a certain depth below the skin surface during treatment [2]
According to Walker (2005), bolus is defined as a tissue equivalent materials which when it is positioned around the irradiated area it results in an additional build up causing the maximum dose to occur at the skin surface [3]

Summary

Introduction

The use of megavoltage photon beams usually exhibit skin sparing effect. This skin sparing effect is advantageous in the treatment of tumours below the skin surface [1]. Skin sparing effect is a major challenge for superficial tumours because it always causes the dose at the skin surface (dsurf) to be lower when compared to the maximum dose at a certain depth (dmax) below the skin surface during treatment [2]. According to Walker (2005), bolus is defined as a tissue equivalent materials which when it is positioned around the irradiated area it results in an additional build up causing the maximum dose to occur at the skin surface [3]. It is expected that the thickness of bolus material for Cobalt-60 energy beam source should be about 0.5 cm since maximum dose usually occurs at a depth

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