9 Reporting in Brachytherapy: Dose and Volume Specification

172 Reporting in Brachytherapy

6.1.4 Need for a common language With the development of computer based dose calculation, there is more freedom for prescribing and performing brachytherapy applications. It is therefore important that a common language is available to report treatments and make exchange of information possible and reliable.

6.2 Dose distribution in interstitial therapy 6.2.1 General description

In interstitial therapy, the dose distribution is non-homogeneous and includes steep dose gradients and regions of high dose surrounding each source. The doses (and the dose gradients) decrease with the distance from the sources.

6.2.2 Local minimum doses Within the volume of the implant, however, there are regions where the dose gradient approximates a plateau (Fig 6.6).

Fig 6.6: Plateau dose region between radioactive sources. The dose distribution shows a plateau region of low dose gradient. In this example of three sources, 6 cm long and with 1.5 cm spacing, the dose varies by less than 2% in the grey region between the sources. (From Dutreix et al., [20])

1°) In an interstitial implant, the regions of plateau dose are equidistant between adjacent neighboring sources, for sources of identical activity. They are regions of „ local minimum doses“ . 2°) Variations between these local minimum doses can be used to describe the dose uniformity of an implant. 3°) A region of plateau dose is the place where the dose can be calculated most reproducibly and compared easily by different departments.