9 Reporting in Brachytherapy: Dose and Volume Specification

158 Reporting in Brachytherapy

2 Clinical Aspects – Volumes It is difficult to report a treatment correctly without a clear idea about the prescription. An accurate and complete view of the aim of the treatment, rationale and prescription is needed to understand the choice of treatment parameters and thus to report the treatment in a relevant way. The clinical status of the patient should be reported as completely as possible, including tumour location and extent, pathology, general status, etc. This information should be reported according to recognized international classification (3,102,103,117). The definition of volumes is of utmost importance, both in external-beam planning and in brachytherapy planning, and the process consists of several steps. Different volumes are defined in this section. The GTV and CTV (44,47) are pure oncological concepts and are thus independent of the treatment strategy, discipline or technique. The Planning Target Volume (PTV) (section 2.3) is in general of lower importance in brachytherapy compared to external beam therapy because the radioactive sources and the target volumes are usually fixed to each other and one does not need to deal with the problem of day to day treatment set up variations. The concepts of Treated Volume and Irradiated Volume are discussed in sections 2.4 and 2.5, respectively. Lastly, the organs at risk in brachytherapy are presented in section 2.6. 2.1 Gross Tumour Volume (GTV) 2.1.1 Definition The Gross Tumour Volume (GTV) is the gross palpable, visible or demonstrable extent and location of the malignant growth. The shape, size and location of the GTV may be evaluated by various diagnostic methods : clinical examination i.e., inspection and palpation, endoscopy, and imaging techniques such as radiography, CT, MRI, PET, ultrasound, or other techniques, depending on the location and type of pathology.

The GTV may consist of : - the primary tumour (GTV-T), - metastatic lymphadenopathy (GTV-N), or - distant metastases (GTV-M). In brachytherapy applications, the GTV is mainly the primary tumour, thus GTV-T.

According to the above definition, there is no GTV after complete ′ gross ′ surgical resection. There is no GTV when there are only a few individual cells or ′ subclinical ′ involvement, even histologically proven. 2.1.2 Recommendations for reporting The methods used to determine the GTV should meet the requirements for scoring the tumour according to the TNM (102,103) and American Joint Committee on Cancer (3) systems, and the definition of the GTV is then in full agreement with the criteria used for the TNM classification.