MRI guided focal therapy is an emerging treatment modality.
At present, overdiagnosis and overtreatment is one of the reasons why prostate specific antigen (PSA) based screening is no longer advocated [1]. Almost 50% of the newly diagnosed prostate cancer patients have low risk cancers. The current standard treatment is based on a whole-organ approach, namely radical prostatectomy or radiotherapy, which has a substantial risk of serious complications, such as incontinence in 15–18% and erectile dysfunction in 8–36%. The majority of these patients receive definitive whole gland therapy with their treatment related morbidity [2]. Focal therapy is a novel strategy for targeted treatment of the main index lesion and may reduce treatment related morbidity. While promising, focal therapy for primary localized prostate cancer remains an experimental modality only. There are major concerns regarding the risk of residual cancer. However, focal therapy also appears to offer rewards in terms of function preservation. Minimal invasive techniques are used to treat organ confined prostate cancer while preserving the healthy tissue. Various energy sources seem to be capable for focal treatment of prostate cancer, for example, focal laser ablation, cryosurgery, high intensity focused ultrasound or irreversible electroporation [3, 4]. In 2010, focal therapy of the prostate was defined, by a consensus panel of radiologists, urologic surgeons, radiation oncologists, and histopathologists from Europe and North America, as: “A type of treatment that aims to eradicate known cancer within the prostate and at the same time preserve uninvolved prostatic tissue with the aim of preserving genitourinary function” [5]. Despite this definition, different anatomical definitions of focal therapy are described in literature: hemiablation (i.e. treatment of the tumor affected lateralized hemisphere of the prostate), hockey stick ablation (i.e. hemiablation of the prostate plus one half of the contra lateral hemisphere) and ‘true’ focal therapy (i.e. only the tumor itself is treated).
THERAPY MODALITIES IN FOCAL THERAPY:
1. Focal laser ablation Laser ablation is an ablation technique, which was originally developed to treatbrain tumors. Laser light is delivered through a fiber and when the tissue temperature around the fiber tip increases >60°C tissue is irreversibly damaged and destroyed. Laser fibers are inserted under image guidance. MRI guidance appears essential in focal LA and might prove to be the only imaging modality for correct targeting of the index lesion, facilitating accurate fiber placement, real-time monitoring of the ablation with the help of temperature mapping, and verification of complete tumor ablation. The total ablation process takes only a few minutes and can be performed in an outpatient setting.
2. High Intensity Focused Ultrasound / non focused ultrasound energy (TULSA) High intensity focused ultrasound (HIFU), is a non-invasive technique. A high intensity ultrasound beam is converged by a transducer and focused at a certain point in the tissue. The energy of the ultrasound waves is sufficient to heat up the tissue and to surpass the thermal dose threshold obligatory for coagulative necrosis in a few seconds. When the transducer consists out of multiple piezoelectric elements, greater flexibility in targeting and shaping of the focal spot can be reached. For prostate cancer, the transducer can be applied transrectal or transurethral. The latter approach is performed by using the combination of real-time MR imaging with transurethral, robotically-driven therapeutic ultrasound and closed-loop thermal feedback control to provide precise ablation of the prostate while simultaneously actively protecting critical surrounding anatomy from potential side effects.
3. Cryoablation: In cryosurgery tumor tissue is ablated by freezing. It is acknowledged as an established treatment option for men with newly diagnosed or recurrent organ-confined prostate cancer by the American Urological Association (AUA) in 2008. Image-guidance is being applied to insert cryoprobes and control the ablation.
1. Loeb S, Bjurlin MA, Nicholson J, et al. Overdiagnosis and overtreatment of prostate cancer. Eur Urol. 2014 Jun;65(6):1046-55.
2. Eggener SE, Scardino PT, Walsh PC, et al. Predicting 15-year prostate cancer specific mortality after radical prostatectomy. J Urol. 2011 Mar;185(3):869-75.
3. Walker NAF, S MRC, Norris JM, et al. A comparison of time taken to return to baseline erectile function following focal and whole gland ablative therapies for localized prostate cancer : A systematic review. Urol Oncol Semin Orig Investig. 2017;1-10.
4. Valerio M, Ahmed HU, Emberton M, et al. The role of focal therapy in the management of localised prostate cancer: A systematic review. Eur Urol. 2004;66:732-751.
5. Rosette de la RJ, Ahmed H, Barentsz J, et al. Focal therapy in prostate cancer-report from a consensus panel. J Endourol. 2010; 24(5): 775-80.