9 Reporting in Brachytherapy: Dose and Volume Specification

206 Reporting in Brachytherapy

8.5 Organs At Risk (OAR): Reference points and volumes

8.5.1 Definition In brachytherapy for uterine carcinoma, the most relevant organs at risk are the rectum, the sigmoid, the bladder, the bowel and the vagina (section 2.6). 8.5.2 ICRU bladder and rectum reference points At the time of publication of ICRU Report 38 (43), an estimation of the dose to “organs at risk” could only be derived from standard orthogonal radiographs of the application. Therefore, reference points were defined in relation to the sources as seen on radiographs (16). 8.5.2.1 Bladder reference point It is related to a Foley balloon in the trigone of the bladder. The balloon is filled with 7 cm 3 of radio- opaque fluid. The catheter is pulled downwards to bring the balloon against the urethra (Fig 6.29). On the lateral radiograph, the bladder reference point is obtained on an AP line drawn through the centre of the balloon. The reference point is taken on this line at the posterior surface of the balloon. On the AP radiograph, the reference point is taken at the centre of the balloon.

Fig 6.29 : Determination of the reference points for bladder and rectum as proposed by Chassagne and Horiot [16].