16. Cervix cancer - The GEC-ESTRO Handbook of Brachytherapy

Cervix cancer

19

THE GEC ESTRO HANDBOOK OF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 01/09/2023

Figure 18. ICRU rectal/recto-vaginal and bladder reference points Diagrammatic representation of the ICRU rectal and bladder reference points (from ICRU 38) and on MRI (from ICRU 89). The ICRU rectal reference point is located 5 mm behind the posterior vaginal wall on an AP line drawn from the centre of the vaginal sources (yellow circle). The ICRU bladder point is positioned at the posterior surface of the catheter balloon containing 7 cm3 of fluid on the AP line passing through the centre of the balloon. Note that both points are defined on the true axial plane i.e. perpendicular to the body axis. If para-axial slices are used for contouring, reconstructed sagittal images should be used to define these points on the axial plane.

Figure 19. ICRU vaginal reference points Sagittal view showing the vagina at the time of brachytherapy with an intracavitary applicator in place. At the level of the vaginal source, dose points lateral to the rings or ovoids can be defined at 0 mm and 5 mm from the applicator surface. The PIBS vaginal-dose point is defined as the point at which a line from the posterior-inferior border of the pubic symphysis crosses the applicator tandem. From there, two additional points 2 cm superior (PIBS+2) and inferior (PIBS-2) along the vaginal axis are defined (From ICRU 89).

Figure 20. Typical dose-volume histogram for (A) residual GTV-T, CTV-T_HR, CTV-T_IR and (B) OAR (From ICRU 89).