Dose distribution verification for GZP6 sources: a comparison of Monte Carlo, radiochromic film, and GZP6 treatment planning system

SUMMARY Background: Treatment planning systems (TPSs) are used for dose calculations in dose delivery by afterload- ing brachytherapy machines. Such planning systems usually use simplified algorithms in their dose calculations. Verification of dose distributions produced by TPS is of clinical importance and is part of a quality assurance program. In this study, the dose distributions generated by GZP6 TPS for two GZP6 sources were verified. Methods: The evaluation was based on the inter comparisons between the isodose curves obtained through Monte Carlo simulations, radiochromic film measurements, and GZP6 treatment planning system. MCNPX Monte Carlo code was used to simulate the sources. Dose measurements were performed in a perspex phantom using Gafchromic® EBT radiochromic films. Comparisons between the results obtained from MC, RCF, and TPS were performed by gamma function calculations with 5% dose/2 mm distance criterion. Results: Based on gamma calculations our results showed that there was good agreement between the dose distribu- tions obtained by the three aforementioned methods in both transverse and longitudinal planes for the GZP6 source No.2. However, for source No. 5, the agreement was good in the transverse plane but it was low in the longitudinal plane. Conclusion: The results showed that dose distributions certified by the GZP6 TPS for the GZP6 source No. 2 were validated. However, for source No. 5 some discrepancies were observed. Accurate knowledge of the activity of each active pellet in the source No. 5 can clarify the cause of the discrepancies.