Brachytherapy: state‐of‐the‐art radiotherapy in prostate cancer

摘要

Contemporary treatment options for prostate cancer are considered to have similar efficacy; therefore, other differences, such as treatment-related toxicities, impact on quality of life, convenience, treatment time and cost, become important considerations in influencing treatment choice. The goal of brachytherapy is to achieve high precision, targeted radiotherapy (RT) using advanced computerized treatment planning and image-guided delivery systems to achieve a tailored ablative tumour dose to the prostate whilst sparing surrounding organs to minimize potential toxicities. Two different brachytherapy techniques can be used to treat prostate cancer: low-dose rate (LDR) brachytherapy, in which radioactive seeds are permanently implanted into prostate tissue or high-dose rate (HDR) brachytherapy, in which the radioactive source is temporarily placed into the prostate via implanted needles. When compared with external beam radiation therapy (EBRT) and radical prostatectomy (RP), both LDR and HDR brachytherapy have similar cancer control 1 and long-term survival rates, with a reduced risk of side effects 2, 3. Brachytherapy is also associated with much shorter recovery times than RP, resulting in less interference to the lives of patients 2, and offers significantly reduced overall treatment times compared with EBRT. When combined with lower infrastructure outlay, it is also cost-effective 4, 5. We would therefore contend that brachytherapy for prostate cancer is an effective, well-tolerated treatment option that offers significant quality-of-life benefits to patients and cost-saving efficiencies to healthcare providers. Patients with localized prostate cancer can be divided into three risk groups according to their pretreatment factors: PSA level, biopsy Gleason score (GS) and clinical tumour staging (cT stage). Combining these prognostic factors allows patients to be separated into three basic prognostic groups or risk classifications: low, intermediate or high risk. There are a number of such guidelines available to define these risk group classifications such as the D'Amico 6, Memorial Sloan Kettering Cancer Centre 7, European Society of Therapeutic Radiation Oncology 8 and National Comprehensive Cancer Network (NCCN) 9 classifications. The American Brachytherapy Society recommends the NCCN guidelines 10: low risk: GS ≤6 and PSA <10 ng/mL and cT stage T1–2a; intermediate risk: GS 7 or PSA 10–20 ng/mL or cT2b–2c; and high risk GS 8–10 or PSA >20 ng/mL or cT3–4. Preoperative evaluation includes CT or MRI of the pelvis, and bone scan in selected patients in the intermediate- and high-risk groups. The use of multiparametric MRI can improve primary tumour staging in patients with intermediate- to high-risk disease, identifying men with advanced T3 disease with >95% specificity 11. It can also assist with radiation planning, improving target volume delineation by identifying extra prostatic extension or seminal vesicle involvement 12. The absolute contraindications to brachytherapy include the presence of distant metastases, absence of rectum, which precludes a TRUS probe and radiation sensitivity syndromes such as ataxia telangiectasia. Although there is no absolute upper or lower age limit for brachytherapy, patients should have a good performance status and life expectancy of at least 10 years. The relative contraindications to brachytherapy include severe urinary obstruction, previous pelvic irradiation, previous TURP, large prostate volumes (>50 mL) and inflammatory bowel disease. The degree of urinary obstruction is assessed by a self-administered IPSS questionnaire 13 and urinary flow rate studies. An IPSS <15, is associated with acceptable rates of urinary toxicity 14-16. If the flow rate study is <15 mL/s and post-void residual urine volume is >100 mL, then management of the BOO is recommended before the brachytherapy treatment. Urinary obstruction may be anatomical in nature, such as bladder neck dyssynergia, urethral stri