9 Reporting in Brachytherapy: Dose and Volume Specification

Reporting in Brachytherapy 199

-a horizontal line tangential to the highest point of the acetabulum, -a vertical line tangential to the inner aspect of the acetabulum.

On a lateral radiograph, the highest points of the right and left acetabulum, in the cranio-caudal direction, are joined and the lateral projection of the pelvic-wall reference point is located mid-way between these points. The dose at the pelvic reference point should be reported. The pelvic-wall reference point is related to fixed bony structures, and not to the applicator as is point B.

8.3.4 Lymphatic trapezoid

Fig 6.26 : Determination of the lymphatic trapezoid. On the left is an anteroposterior view and on the right a lateral view (see text). (From Fletcher (25))

Different points identified by means of the lymphatic trapezoid of Fletcher [25] are intended to be representative of the absorbed dose to the mid-external iliac-, low-common iliac- and low para-aortic lymph nodes. The lymphatic trapezoid is obtained as follows (Fig 6.26): -a line is drawn from the junction of S1-S2 to the top of the symphysis, -then a line is drawn from the middle of that line to the middle of the anterior aspect of L4, -a trapezoid is constructed in a plane passing through the transverse line in the pelvic brim plane and the midpoint of the anterior aspect of the body of L4, -a point 6 cm lateral to the midline at the inferior end of this figure is used to give an estimate of the dose rate to mid-external iliac lymph nodes (labelled R.EXT and L.EXT for right and left external respectively), -at the top of the trapezoid, points 2 cm lateral to the midline at the level of L4 are used to estimate the dose to the low para-aortic areas (labelled R.PARA and L.PARA), -the midpoint of a line connecting these 2 points is used to estimate the dose to the common iliac lymph nodes (labelled R.COM and L.COM).