21 Urinary Bladder Cancer

Urinary Bladder Cancer

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THE GEC ESTRO HANDBOOK OF BRACHYTHERAPY | Part II: Clinical Practice Version 1 - 21/04/2015

After the procedure, a Foley catheter is introduced to remain in place during the irradiation period. Because of the straight path between the bladder wall and the abdominal wall, kinking of the catheters seldom occurs with this technique (Fig 22.11). However, even with the laparoscopic technique it is advisable to place a synthetic or metal wire in the catheter to prevent kinking during the course of the treatment. A further development of the Arnhem technique is the robot-as- sisted laparoscopic implantation technique, which facilitates ac- cess to difficult bladder locations such as the bladder neck. Fur- thermore the console makes it possible to look at the endoscopic intravesical and laparoscopic views simultaneously.

report 58 recommendations, the ratio prescription isodose over the Mean Central Dose (85% in a non-dwell time optimized Par- is system implant) should always be recorded and reported (26). One to two days after the suprapubic approach or a few hours postoperatively after a laparoscopic procedure, a CT-scan is done for treatment planning. Catheters can be reconstructed from the CT-scan. The markers or spacers indicate the target volume length. Marking the target volume length is necessary to decide on the position of dwell sources that are activated. Contouring of the CTV can be done by delineating the full blad- der wall in between the spacers or titanium markers.

Fig 22.11: Orthogonal x ray of a laparoscopic interstitial bladder implant. The nearly straight plastic tubes leave the abdomen laterally in the abdominal walls, avoiding any risk of kinking of the tubes.

Fig 22.12: Bladder wall implant with stepping source afterloading catheters. Intravesical spacers assure equidistant parallelism of the implanted source carriers.

9. TREATMENT PLANNING

For optimal dosimetry, catheters should be placed parallel and equidistantly (Fig 22.12). One method is by implanting accord- ing to the rules of the Paris system (See chapter 7). Source spacing at the time of implantation is chosen so that the full thickness of the bladder wall is treated (Fig 22.13). The thick- ness of the bladder wall is measured with a circular calliper (Fig 22.14) or any other measuring device. If the area is difficult to reach, then the thickness can be estimated between finger and thumb or measured on a recent CT/MR image. CT or MR imaging should be performed before the TURB or at least 4 weeks after TURB. Catheter spacing of 10 to 20 mm will result in a treated volume of 5 to 12 mm thick. Provisional dosimetry can be done according to the Paris-system implanta- tion rules by calculating the proper catheter spacing (see chapter 7) to guarantee adequate coverage of the target thickness (Fig 22.15). For 3D dosimetry on CT-scan, geometrical optimization and slight dwell time adaptations can be done for optimisation of the dose distribution to correct for inaccuracies of implantation. Another method of dosimetry is by prescribing to dose points (25). With this method, the dose points are 5-7 mm from the sources, depending on the bladder wall thickness. It is impor- tant to verify the coverage of the target volume on the planning CT-scan and to evaluate the high-dose volumes. For example the 150% isodose volumes around the individual catheters (source tracks) should not merge with each other and preferably not be larger than 7-8 mm in transverse diameter to avoid necrosis. Whatever the prescription isodose chosen, following the ICRU

Fig 22.13: CT-scan overview of a bladder implant in the left dorsal wall just cranial to the trigonum.

Fig 22.14: Circular calliper to measure tumour size and bladder wall thickness.