Refined Sievert Integral for The Calculation of Dose Distribution Around the New Bebig Co-60 High Dose Rate Brachytherapy Source

ABSTRACT

A very good reason why calculation of dose distribution is important is that it is essential to plan and replicate the treatment prior to the actual delivery of the radiation dose to the tumour. In modern radiation therapy, computer software is used for performing treatment planning. Different algorithms are employed at every stage of treatment including dose calculation algorithms. The dose calculation used for the HDRplus TPS is the TG43 formalism and just like every other TPS, the HDRplus, version 3.0.5, may produce erroneous results, (Daskalov, 1998) and it is essential to eliminate or reduce these errors through a quality control procedure of manual calculations. This will further improve treatment outcomes since TPS approximations are used in executing treatment. The Sievert integral algorithm is commonly used in radiotherapy treatment planning systems (RTPS) for evaluation of dose around brachytherapy sources and it is an established tool for 125I, 169Yb, 137Cs and 192Ir (Bhola et al, 2012). The source under consideration is the new model (Co0.A86) of the BEBIG 60Co HDR source, hence the need to establish the Sievert as a valid tool for quality control for the output of the TG43 based HDRplus TPS using this source.

From the results obtained, the percentage deviation range of the dose output from the Sievert integral in comparison to that of the output from the TPS is 0.03 – 10.51% with a mean of 3.13% for angle range of 0 o < θ < 70o . The Sievert integral breaks down at respectively large angles and therefore neglecting the breaking point oblique direction, i.e. , the range becomes 0.03 – 5.63% with a mean value of 2.55% for the angle range of 0 o < θ < 48o . Following the ICRU report 24 that percentage deviation of dose values calculated should not exceed ±5% of the true value, the Sievert integral has proven to be a valid tool for quality control of the HDRplus using the range with less error. 1 C