20 Prostate Cancer

Prostate Cancer

9

THE GEC ESTRO HANDBOOK OF BRACHYTHERAPY | Part II: Clinical Practice Version 1 - 01/12/2014

a. TRUS, stepper unit showing cradle for ultrasound in position and template holder

Cradle

Template holder

Control wheel for forward and backward movement of cradle

Fig 21.5: TRUS for LDR implant Urethra is placed along row D and the inferior border is within row 1

In the past the volume study was done separately and followed later by the actual implantation, the so called preplanning. A dis- advantage of this technique is the difference in position of the patient, the volume study in this setting often being performed without anaesthesia unlike the implant procedure. One advan- tage of preplanning is to test for pubic arch interference and to exclude those patients with a large volume for whom antiandro- gen cytoreduction is indicated. It also enables the precise num- ber of seeds required to be calculated and is essential if preloaded needles are to be ordered. In most centres today preplanning has been replaced by a ‘one- step’ procedure with the volume study done on the treatment table under anaesthesia directly before the insertion of the nee- dles.This eliminates positional errors, but takes more time in the operating room. Improved implant dosimetry over the conven- tional ‘two stage’ approach has been demonstrated which could translate into improved biochemical control [22][23]. Interactive planning is a further development in which the plan- ning process is performed real time during the insertion of the needles. This is usually based on a preplan and as the needles are placed in position their precise location is mapped with adjust- ments made in the plan as the implant progresses to optimise the actual distribution achieved. The distance from the outer wall of the bladder base to template is determined. This is used as a reference for retraction of the nee- dle tip from the base. The radioactive seeds are inserted through 20 cm long 18 gauge needles. These can either be preloaded or afterloaded once correctly positioned within the prostate. The planned loading pattern indicates the X and Y co-ordinates of each needle, the number of seeds in each needle and the re- traction of each needle tip from the reference base plane for the location of each seed (the Z co-ordinate).

b. Ultrasound positioned on cradle being passed per rectum in preparation for implant

Fig 21.4

8.1 Permanent implants Since intra-operative planning is the most widely used technique and the preplanning technique is not much different, only this technique is described here. To reduce prostate movement during the procedure two or three stabilising needles may be inserted; A volume study is performed in which transverse images of the prostate are taken every 5 mm from base to apex. Superimposed on the ultrasound image is a template matrix. The volume is de- fined on each ultrasound slice (Fig 21.5) and the images are en- tered into a dedicated treatment planning system to determine the exact number and position of seeds required to deliver the prescribed minimal peripheral dose to the margins of the tar- get volume. With many systems 3D images can be acquired for delineation of the prostate contour, resulting in a more accurate prostate volume.