20 Prostate Cancer

Prostate Cancer

13

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

T2-disease and extended to include any extracapsular or seminal vesicle extension in T3 disease. Other subvolumes containing areas of macroscopic tumour defined on imaging or template bi- opsies may also be defined and will be designated CTV2 CTV 3 etc. The planning target volume is defined by the CTV1 incorpo- rating a margin for uncertainties typically of 3mm constrained to the bladder base and anterior rectal wall. This can be defined using ultrasound as shown in figure 21.8, CT as shown in figure 21.9, or MRI. The influence of prostate-water-rectal-displacement-kit (PWDK) on the catheter, prostate gland and rectum geometry and do- simetry has been investigated [35]. PWDK enables individual adjustments of water filling for achieving adequate US-image quality and to enable a better accessibility of the prostate gland at its dorsal extend via needles inserted through the template holes. In order to reduce the dose to rectum after the final image ac- quisition and planning either the water in the PWDK is emptied or the whole US-probe is removed. Even when 18-20 metallic needles have been inserted there is a movement of the prostate (probably decompression of the dorsal region) independently of the needles. The needles remain in place but the decompres- sion of dorsal prostate results in increased distance of the dor- sal border from the most dorsally implanted needles. This effect is expected to be most pronounced when the probe as whole is removed and will result in a reduction in the rectal dose.,with uncertainties over the dose delivered and DVH-based values for both CTVs/PTV and rectum itself. The 4D study results for 3D-transrectal ultrasound based treatment planning and treat- ment with unchanged patient positioning and the ultrasound probe remaining in rectum during delivery has demonstrated that under those stable conditions a stability of anatomy and im- plant of such high as 1.0 mm can be achieved during the whole period from planning to delivery [36]. The ESTRO/AAPM re- port [37] shows that under those conditions a total dosimetric uncertainty in the treatment delivery of up to 5% (for k=1) can occur. When treatment planning is based on US, then real-time in- traoperative planning technology utilizing 3D-US offers the best possible workaround for defining target volumes e.g. pros- tate gland (CTV 1) in the presence of needles. More advanced US-imaging technology can help in overcoming partly the diffi- culties of identifying the ventral gland border. There is some potential for biological planning with the use of Doppler sonography or matching of TRUS + MR spectroscopy, functional CT or MR images or 11C-choline PET. Usually, by the use of inhomogeneous dose distributions, about 20-40 % of the CTV1 volume can receive at least double the prescribed dose due to the high inhomogeneity of the dose distribution, this may be exploited in focal therapy. The planning aim doses and the dose prescription for HDR brachytherapy [17] are not fixed after external beam delivering a dose of 45-46Gy in 23-25 fractions. A single dose of 15Gy for CTV1 is increasingly being adopted. However, alternatives in- clude 15Gy in 3 fractions or 11-22Gy in 2 fractions. When HDR is used as monotherapy the following planning aim doses have been recommended: 34-38Gy in 4 fractions, 31-33Gy in 3 frac- tions or 26Gy in 2 fractions [17] Focal prostate brachytherapy Improved imaging using multifocal MR and choline PET to-

gether with transperineal template biopsies now enables the dis- tribution of cancer within the prostate to be defined with some accuracy. Based on this there is increasing interest in focal brachytherapy for low-risk localized prostate cancer rather than conventional whole gland brachytherapy [37][38]. In practice this may take two forms: i) Whole gland treatment with a focal boost to defined dominant lesions, now termed ‘focussed’ treatment ii) Focal therapy to the dominant lesion(s) alone. This may take the form of hemi-gland treatment covering the half gland containing tumour or true focal treatment to the dominant lesion alone. Patient selection and implant technique will be as described above except that for focal implants a CTV 2 will be defined and with LDR a greater concentration of seeds implanted in that area and for HDR additional catheters or needles will be required. So far, focal primary treatment seems safe and feasible, but no long term follow up has been described yet [37]. It is therefore cur- rently an experimental approach and cannot be recommended outside a clinical trial. There are some existing interdisciplinary/ international consensus meeting results and review publications advising enrolling criteria for such prospective investigations [37][39][40]. Patients can be discharged from hospital the same or the follow- ing day after completion of seed implantation and HDR treat- ment delivery. Before the patient leaves the hospital he receives instructions for radiation safety and how to manage voiding problems. Many centres prescribe an alpha-blocker to enhance the urine flow and a week of prophylactic antibiotics. Following HDR brachytherapy there are no radioprotection is- sues however after seed brachytherapy, whilst the dose outside the patient is very low and within radiation safety limits it is usu- al to recommend that for the first two months after implant chil- dren do not sit on the lap of the patient. Occasionally loose seeds migrate through the urethra and these should be picked up using a long handled tool such as a spoon and disposed of through the patient’s sanitary disposal system. For men who resume sexual activity condom use is recommended for the first two months to prevent transfer of seeds to their partner, again a very unlikely event. Cremation can cause contamination of the crematorium and liberate radioactive material into the atmosphere; it is usu- ally therefore recommended that this is not undertaken in the first two years after seed implantation. Written information re- garding the sources, radiation strength, date of implantation and contact numbers should be given to the patient for him to carry with him. After seed brachytherapy patients will usually return at 4 to 6 weeks for post implant dosimetry and clinical review. Subse- quent follow up appointments should be made at least 6 monthly in the first year and annually thereafter. Long term follow up is 11. MONITORING