Dosimetric analysis of intracavitary brachytherapy applicators: a practical study.

Purpose: Intracavitary brachytherapy is one of the important methods of gynecological cancer treatment. The effect of attenuation is not considered in the dose calculation method released by the American Association of Physicists in Medicine (AAPM) Task Group No. 43 Report (TG-43). In this study, the effect of high-dose rate (HDR) brachytherapy applicators on dose distribution was measured using Gafchromic films and well-type ionization chamber.

Materials and methods: A plan created by the treatment planning system was first executed using a well-type ionization chamber with a water equivalent elasto-gel in place for charge collection. Again, same plan was executed using central tandems of various angulations with different diameters of vaginal cylinders and charge collection was measured. For in vitro dose measurements this plan was also executed on tandem and vaginal cylinder assembly with Gafchromic films fixed on the surface of vaginal cylinder.

Results: The results show that the central tandem when used with different vaginal cylinders resulted in increase in effective attenuation of the beam. The central tandem of 300 angulations when used with a 35-mm diameter vaginal cylinder results in maximum attenuation whereas the 0º tandem when used with 20-mm diameter vaginal cylinder results in least attenuation of the beam.

Conclusion: Due to the attenuation by various applicators used in brachytherapy for the treatment of gynecological cancers, it can be concluded that the difference between practical dose and the treatment planning system calculated dose should be considered for the correct estimation of the dose to the target and the organs-at-risk.