16 Cervix Carcinoma

342 Cervix Cancer

Therefore, changes may be helpful to increase the usefulness of the ICRU 38 recommendations for the future. Furthermore, as shown in a recent GEC ESTRO-survey on the use of these ICRU 38 recommendations (97), major parameters, in particular TRAK and 60 Gy reference volume have been poorly reported in clinical practice and in published work, and hardly ever from centres using HDR brachytherapy. Furthermore, there has been no common language for reporting time dose pattern between the traditions based on LDR, MDR, and HDR brachytherapy. Therefore, a more comprehensive approach must be developped taking into account the different dose rates applied and the different imaging methods which are being increasingly used. The concept of „Reference Volume“ was introduced by the ICRU on the background of LDR brachytherapy. The dose level selected to define the reference volume may need to be adapted to take into account the development of HDR and PDR. When modifying the time-dose pattern, weighting factors have to be evaluated (based on established biological models) and applied to the quantity “absorbed dose” to obtain another quantity, the “Biologically Weighted Dose”, that has to be correlated with the biological/clinical effects. It must be kept in mind, when modifying the time-dose pattern, that the weighting factor is not a unique/single value, but varies significantly with dose, dose rate, tissue or effect. Therefore, the tissue/effect for which the weighting factor is evaluated (and the numerical value of this weighting factor) should always be reported in addition to the (physical) absorbed dose. In order to allow integrating the traditional methods of reporting based on point concepts and more recent methods based on volume concepts, different „levels for reporting“ are identified in brachytherapy, in the same way as proposed for external beam therapy in ICRU Report 50 (see chapter 6). At level 1 - 2, doses at accurately defined „point A“ and ICRU recommended reference points can be reported, while for the same applications , level 2-3 includes reporting the dimensions of volumes encompassed by different isodose surfaces (including isodose through point A, 60-Gy Reference Volume, Treated Volume, Organ Volumes). In any case, reporting at level 2 shall always include all information that should be reported at level 1. Reporting on points and volumes will allow for a common language which makes either practice understandable to everyone. As an example for such proposal, the direct correlation between the “60 Gy volume”, the “85 Gy volume” and the “dose to point A” is illustrated for a given source geometry (Fig 14.16). The volume concept stays closely connected to the reporting of doses at specific points, such as a well defined “point A” (level 1). The different levels for reporting will have to be clearly defined and will become integrated. Dose to points and volumes in the target and in critical organs will become determinable in a valid, reliable and reproducible way, if in addition to traditional practice, the potential of modern imaging and computer technology is adequately taken into account (for more detail see chapter 6 on reporting, in particular 6.8).