9 Reporting in Brachytherapy: Dose and Volume Specification

Reporting in Brachytherapy 165

the manufacturer should be mentioned. However, any variation between the published conditions and that actually used should be mentioned. If new types of sources, applicators or techniques are used, a full description is needed.

3.5 The “Systems“ The term “system” (ICRU, Report 38,(43)) denotes a set of rules taking into account the source strengths, geometry and method of application in order to obtain suitable dose distributions over the volume(s) to be treated. For reporting, the system includes recommendations for specifying the application and possibly, as in the Manchester System, for calculating the dose rate (or the dose) at specific points. The “historical“ systems mentioned in the present chapter were developed in a period where computer treatment planning and dose computations were not yet available. In brachytherapy applications, a “system“ ensures safety insofar as it implies application rules and is based on clinical experience. If a system is followed, it must be followed for (1) prescription, (2) application of the sources in space and time and (3) reporting. If a standard system has been followed, it must be specified and this facilitates reporting. If it is not the case, the source pattern should be described completely and unambiguously. Development of computers and easy availability of complete dose distribution (which is per se a benefit) tends to increase the use of “no system“ applications.

4 Specification of the Source “Strength” (Intensity) in Brachytherapy

A clear distinction should be made between specification of the sources, dealt with in this section, and specification of the doses to the patient organs or tissues, dealt with in sections 6, 7 and 8.

4.1 Reference Air Kerma Rate (RAKR) As a general recommendation (ICRU, Reports 38 and 58 (43,45)), the “strength” (intensity) of photon emitting radioactive sources for brachytherapy should always be specified in terms of the quantity ”Reference Air Kerma Rate“ (RAKR). The problem of specification of sources in brachytheray is an important one. A new concept has been introduced with the aim of replacing the activity (contained or ”apparent“) in a source by the “output“ from the source. This concept has been discussed by several authors, and the quantity Reference Air Kerma Rate has been increasingly adopted by different organizations and commissions (2,4,9,11,15,17,21,41,60,61,69,71,72,98,114). 4.1.1 Definition The Reference Air Kerma Rate (RAKR) of a brachytherapy source is the air-kerma rate, in vacuo , at a reference distance of 1 meter from the source centre, on its transverse axis due to photons of energy greater than δ.