A quantitative three-dimensional dose attenuation analysis around Fletcher-Suit-Delclos due to stainless steel tube for high-dose-rate brachytherapy by Monte Carlo calculations

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 Task Group No. 43 Report. In this study, the effect of high-dose rate 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.

Physics-aspects of dose accuracy in high dose rate (HDR) brachytherapy: source dosimetry, treatment planning, equipment performance and in vivo verification techniques

This study provides a review of recent publications on the physics-aspects of dosimetric accuracy in high dose rate (HDR) brachytherapy. The discussion of accuracy is primarily concerned with uncertainties, but methods to improve dose conformation to the prescribed intended dose distribution are also noted. The main aim of the paper is to review current practical techniques and methods employed for HDR brachytherapy dosimetry. This includes work on the determination of dose rate fields around brachytherapy sources, the capability of treatment planning systems, the performance of treatment units and methods to verify dose delivery. This work highlights the determinants of accuracy in HDR dosimetry and treatment delivery and presents a selection of papers, focusing on articles from the last five years, to reflect active areas of research and development. Apart from Monte Carlo modelling of source dosimetry, there is no clear consensus on the optimum techniques to be used to assure dosimetric accuracy through all the processes involved in HDR brachytherapy treatment. With the exception of the ESTRO mailed dosimetry service, there is little dosimetric audit activity reported in the literature, when compared with external beam radiotherapy verification.

Independent evaluation of an in-house brachytherapy treatment planning system using simulation, measurement and calculation methods

Accuracy of treatment planning systems may significantly influence the efficacy of brachytherapy. The purpose of this work is a detailed, varied and independent evaluation of an in-house brachytherapy treatment planning software called STPS. Operational accuracy of STPS was investigated. Geometric tests were performed to validate entry and reconstruction of positional information from scanned orthogonal films. MCNP4C Monte Carlo code and TLDs were used for simulation and experimental measurement, respectively. STPS data were also compared with those from a commercial planning system (Nucletron PLATO). Discrepancy values between MCNP and STPS data and also those of PLATO and STPS at Manchester system dose prescription points (AL and AR) of tandem and ovoid configurations were 2.5% ± 0.5% and 5.4% ± 0.4%, respectively. Similar results were achieved for other investigated configurations. Observed discrepancies between MCNP and STPS at the dose prescription point and at 1 cm from the tip of the vaginal applicator were 4.5% and 25.6% respectively, while the discrepancy between the STPS and PLATO data at those points was 2.3%. The software showed submillimeter accuracy in its geometrical reconstructions. In terms of calculation accuracy, similar to PLATO, as attenuation of the sources and applicator body is not considered, dose was overestimated at the tip of the applicator, but based on the available criteria, dose accuracy at most points were acceptable. Our results confirm STPS's geometrical and operational reliability, and show that its dose computation accuracy is comparable to an established commercial TPS using the same algorithm.