Background:The aim of this study is to design and fabricate a thorax phantom with irregularly shaped trapezoidal slots across the left side of the chest wall, allowing for the creation of unwanted air gaps under the bolus. Method: Surface dose (D surf ) measurements were made with Gaf Chromic EBT3 films at air gaps (0.0, 5.0, 10.0 and 15.0 mm) under gel bolus of thickness (5.0 mm & 10.0 mm), for 3DCRT technique (2 and 3 field) with clinical 6 MV photon beam under uniform and non-uniform air gap condition. The obtained values were compared with TPS estimated ones. Results: In the presence of 15.0 mm uniform air gap, the mean estimated and measured D surf values with two and three field techniques decreased by 14.0 % to 15.2% and 14.7% to 17.4% under 5.0 mm and 10.0 mm bolus applications respectively. In presence of non-uniform air gap condition, the effect on D surf was minimal (3 to 3.5%) compared with the uniform air gap condition. Conclusions: Based on the study's findings, it is recommended that when using bolus in clinical radiotherapy applications, special care be taken to avoid unwanted air gaps under the bolus in order to achieve a uniform surface dose across the treatment region, where a customized 3D printed bolus may be a better option.
Background: Aim of this study is to evaluate the efficacy of inhomogeneity corrections calculated by radiotherapy treatment planning system (TPS) using various densities of materials. Materials and Methods: Gammex Computed tomography electron density inserts (EDI's; 14 no's) were used to generate the CT to ED curve with high speed GE CT scanner by noting down the respective HU values of each rod. Treatment plans were generated in XiO TPS with three inhomogeneous phantoms (comprising combination of water, lung and bone equivalent slabs) with different field sizes and for EDI (8 no's) inserted in slots of acrylic tray and validation was carried out using 2D array detector with 20cm×20cm field size for 200 MU. Point dose and fluence measurements were carried with inhomogeneous phantoms combinations and EDI's (placed on the locally fabricated box filled with water medium). Results: The mean percentage deviations with standard deviation of calculated point doses against measured ones obtained with 2D array detector at iso-center plane for all three inhomogeneous phantom combinations were found to be -1.13%±0.13%, -3.51%±0.14% and -0.63%±0.27% respectively. On point doses measured under each individual EDI, over all percentage deviation with standard deviation observed is -2.04% ± 1.1%. Conclusion: The described method can be implemented in any newly established radiotherapy department as a routine quality measure of TPS to verify its efficacy in performing of inhomogeneity calculation.
HDR brachytherapy source (Ntekim et al., 2010). The anisotropy, radial dose function, and qualitative isodose distributions produced by the Co-60 source have been reported to be comparable to those produced by the Ir-192 source (Strohmaier et al., 2011). Other studies on
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