20 Prostate Cancer

Prostate Cancer

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

It is usual to start implantation with the anterior needles in or- der to minimise ultrasound interference during the course of the implant. Each needle is inserted into the preplanned co-ordinate and advanced until it is visible in the ultrasound plane, which is set to define the depth (Z co-ordinate). An alternative way of defining the needle position is by sagital imaging with the ultra- sound probe. With pre-loaded needles, the seeds are immediately deposited in the prostate. With an afterloading technique, either all needles or each row by row is placed in position before the seeds are deposited. The afterloaded seeds can be single seeds as with a Mick applicator or the FIRST system or stranded or linked seeds which are connected to reduce the possibility of seed migration and loss during voiding [24]. There is no firm evidence to show better results with one technique or the other, although one study has shown an advantage with no seed migration seen after the use of stranded seeds [25]. Once the implant has been completed the coverage of the pros- tate can be checked both by ultrasonography and fluoroscopy. With fluoroscopy the number of seeds can be counted to ensure all seeds can be accounted for before leaving the implant area. Cystoscopy can be performed at the end of the implant to re- move any loose seeds. This is not absolutely necessary as it is a rare event and they will usually pass spontaneously and most centres no longer include cystoscopy. The bladder catheter can be removed at the end of the procedure although after spinal anaesthesia it may be preferred to retain it until sensation has returned.. 8.2 Temporary HDR implants Temporary brachytherapy uses implanted applicators (catheters or needles) which are then loaded using the remote control af- terloader. This may be given before or after a course of external beam therapy with no evidence to suggest one approach is better than the other or as monotherapy within a clinical protocol. The principles of transrectal ultrasound pre-planning and needle placement under ultrasound guidance are similar to those used for permanent seed implants [26]. The patient is set up with the TRUS in position and using a stepping frame with a template; the urethral plane is defined along the central row which is then avoided when inserting catheters. The distance between the low- est row of sources and the rectum should be maximised and the this lowest row of catheters should if required cover the semi- nal vesicles. In the majority of techniques rigid needles or plastic catheters are used which are maintained in position by a perineal template. The usual principle of applicator placement to cover the CTV uniformly is achieved by placing applicators at approxi- mately 1cm spacing around the periphery of the gland with a sec- ond inner core to provide dose to the central gland. As with LDR seed implants the periurethral zone will be kept free of seeds. If the seminal vesicles are to be included in the implant then it is important when setting the patient up to ensure that the base row of the template includes these structures. Free hand implanted catheters with the template removed may be used by experienced teams to maximise seminal vesicle and peripheral cover. The first possible source dwell position lies some millimetres from the catheter tip and therefore the tip of the catheters needs

to be pushed well up to the bladder base to make sure that the base of the prostate is adequately covered. This can be monitored by cystoscopy which will demonstrate tenting of the bladder mucosa as the tip of the catheter reaches the base. Others rec- ommend that the catheters pass through the bladder base com- pletely to ensure adequate coverage of the base of the prostate. On completion of the implant imaging is required to define the CTV and the source positions within the catheters. In cases where plastic needles are used, the obturators used for needle insertion and guidance have to be removed prior to final image acquisition for the treatment planning. Imaging may use TRUS with the patient still anaesthetised in the operating room and in lithotomy position [17, 26] or CT/MR following transfer after recovery from the anaesthetic. This data will then be used for the treatment planning process to optimise the dwell positions of the source within the catheters so that the dose to the urethra and rectum can be minimised while at the same time ensuring adequate cover of the tumour with a boost to sites of macroscop- ic disease if they are identified. When multiple fractions are delivered through a single implant the tip of the catheters may move in relation to the bladder base between fractions and it is important that there is a means of ensuring accurate catheter position based on re-imaging before each fraction employing good quality assurance procedures [27]. This may be avoided by using catheters with anchoring wings [28]. After completing the treatment, the needles and any in-vivo dosimetry devices can be removed. This is usually atraumatic with any superficial bleeding readily controlled by a short pe- riod of compression. The urethral catheter can also be removed although occasionally where the catheters are advanced to the bladder base bruising may result in haematuria which requires an additional period of bladder irrigation. Pulsed Dose Rate (PDR) afterloading brachy- therapy The technique for PDR brachytherapy is the same as for HDR brachytherapy using the same range of applicators and afterload- ing equipment.

9. TREATMENT PLANNING 10. DOSE, DOSE RATE, FRACTIONATION

LDR permanent implants Permanent seed implants can be performed either with Io- dine-125, Palladium-103 or Caesiun-131. The half-life of iodine is 59.49 days, 16.991 days for palladium and 9.689 days for cae- sium. Palladium and iodine emit photons of very low energy ra- diation (21 to 28 keV), where caesium emits photons of slightly higher energy (29 to 34 keV) so that radiation protection is eas- ily achieved [29][30]. Palladium and caesium are not popular in Europe, and the vast majority of implants are with iodine seeds. Typical initial seed strengths used for permanent prostate im- plants are in the range of 0.5-1.0 U (0.4-0.8 mCi) for Iodine-125,