9 Reporting in Brachytherapy: Dose and Volume Specification

Reporting in Brachytherapy 183

7.2.3 Shape of volumes The volume encompassed by an isodose close to the sources (see below Treated- and Reference Volumes, section 6.7.5) has a “cigar” or cylindrical shape, depending on the distribution of radioactivity in the source. For a wire source with homogeneous linear activity, or for a series of seeds with equal activities, the diameter decreases as the extremities are approached (“cigar” shape). This can be deliberately compensated for by increasing the activity near the end of the linear source (e.g., seeds of different activities, moving source with different dwell times, etc.). 7.3 Clinical aspects The definitions and general recommendations for reporting from section 2 (p. 158) are applicable (compare for more details Chapter 24 on Oesophagus. However, the organs suitable for intraluminal brachytherapy have a central lumen containing the applicator. The dose to the volume occupied by the lumen and the applicator is obviously not relevant. Therefore, the main dimensions to evaluate and to report are the length and the tissue depth (thickness). 7.3.1 Length and depth of the GTV, CTV, PTV The length and depth of the GTV, CTV, and PTV should be reported (see Fig 24.3, 24.6, 24.8; 32.4). The lengths of the GTV, CTV and PTV are defined at the level of the mucosa (in contrast to the Treated- and Reference Volume, which are defined at the reference depth, see section 7.5). The depths of the GTV, CTV and PTV are defined in relation to the luminal surface. As discussed previously (see Section 2), delineation of the CTV and PTV depend on the judgement and experience of the radiation oncologist. 7.3.2 Lumen - Lumen diameter The organs suitable for intraluminal brachytherapy have a lumen and, depending on the site, the lumen diameter may be measured using appropriate diagnostic procedures, such as radiographs with contrast medium, endoscopy, CT, MRI, US. If the lumen is completely filled by the applicator, the lumen diameter becomes identical to the applicator diameter (vagina, oesophagus, see 7.4.2). The reference lumen diameter is defined in the central plane (see section 7.4.1). If this is not relevant (e.g., due to the presence of tumour stenosis which is maximal distally or proximally), an average lumen diameter should be chosen around the central plane. 7.3.3 Specific clinical aspects in endovascular brachytherapy Although the concepts defined above for intraluminal brachytherapy are in general applicable to endovascular brachytherapy, some of them need modification and new definitions have been introduced by the GEC ESTRO (86). Lesion length The lesion length is defined as the stenotic or occluded length of the vessel segment. Its proximal and distal ends must be specified according to strict criteria (e.g., >50% reduction of the lumen diameter as seen on the angiogram). The lesion length must be reported so that patients can be compared related to their prognosis.