9 Reporting in Brachytherapy: Dose and Volume Specification

184 Reporting in Brachytherapy

Interventional length The interventional length is defined as the angioplasty length or the distance covering any part of the vessel where the intervention took place. The interventional length must be reported so that patients can be compared in relation to the efficacy of endovascular brachytherapy (Fig 32.4). The concept of interventional length may have some analogy with the concept of GTV in oncology. Length and depth of the Clinical Target Volume In endovascular brachytherapy, the length and depth of the Clinical Target Volume (CTV) is the length or depth to irradiate: it should include the whole injured part of the vessel wall (Fig 32.4). The length of the injured vessel wall is larger than the interventional length because dissection may occur in the vessel wall beyond the inflated balloon length. 7.4 Reference points for reporting intraluminal brachytherapy Following the ICRU (48), a clear distinction should be made between specification of the sources (at a distance from the source (section 4.3, p. 187) and specification of the dose to the patient (see Fig 6.19 and 6.20B,C) For reporting irradiation of the patient (or the Target Volume), a set of 3 reference depths/points (independent of the treatment technique) are defined: ►the surface (mucosa) itself (Fig 6.18-20); ►the Minimum Target Dose. ►a reference depth of 5 mm in the tissues, from the surface (mucosa) (Fig 6.18-20); Before defining the reference points, lengths and volumes to be reported, it is necessary to define the “central plane” of the application to which these points, lengths and volumes are referred. 7.4.1 Central plane The central plane of an intraluminal application is the plane perpendicular to the axis of the organ lumen, half way between the proximal and distal ends of the PTV. This definition is analogous to the definition of the central plane of an interstitial implant (see section 6.2.3). The central plane is used for prescribing and reporting. The reference points, lengths and volumes to be reported should be defined in the central plane. The central plane is also used to define the average lumen diameter, as indicated in section 7.3.2). 7.4.2 Dose at the luminal surface The dose at the mucosa represents the highest (maximum) dose in the PTV, and is thus clinically relevant in relation to tumour effects and/or complications. Reporting the dose at the luminal surface, in the central plane, is therefore recommended. If, because there is a large irregular tumour, the mucosal dose in the central plane itself is not representative, an average mucosal dose around the central plane may be more relevant to report.