Dosimetric evaluation of Gammamed High Dose Rate intraluminal brachytherapy applicators

Abstract

Background

A survey of the literature on intraluminal brachytherapy reveals that even for a given tumour site, the dose prescribed varies considerably from one centre to another for multiple reasons: the treatment intent, the association with external beam therapy or not, the dose rate, the technique used and the point of dose specification. There is no common language in the literature as to how doses should be recorded and reported.

Aim

The purpose of this study was to dosimetrically evaluate various intraluminal brachytherapy applicators for the Gammamed high dose rate afterloading system.

Materials/Methods

Dosimetric evaluation was carried out for 8mm, 10mm, 12mm and 14mm diameter intraluminal applicators available with the Gammamed high dose rate after-loading system. Treatment planning for these applicators was carried out with the Abacus treatment planning system for active source length and 8cm, 10cm and 12cm. All evaluations were carried out for a prescription dose of 5Gy at the reference point of 1cm from the source axis. Reference volume length (RVL), treated volume (TV) and hyperdose sleeve radius (HSR) were noted down from the isodose plans. Iterative, geometric and equal times optimization routines were carried out for all evaluations with step size of 0.5cm.

Results

The isodose curves showed tapering pattern towards the distal and proximal regions. The reference volume lengths were larger than active source lengths for 8mm and 10mm diameter applicators. Reference volume lengths were smaller than active source lengths for 12mm and 14mm diameter applicators hyperdose sleeve radius decreases with increase in diameter of the applicator. For 14mm diameter applicators, the hyperdose sleeve radius was smaller than the radius of the reference isodose. Iterative optimization routine gave a better average in terms of reference volume length for all four diameter applicators.

Conclusions

We evaluated the dosimetric parameters for various intraluminal applicators available with the Gammamed high dose rate remote afterloading system. The values of RVL and HSR were within acceptable limits for the four applicators considered in this study.