Table 4 Summary of focal therapies.
Mechanism of action | Treatment approach | Indications/ contraindications | Strengths/ limitations | Important studies | Stage of modality | |
|---|---|---|---|---|---|---|
Transrectal MRI-guided focused ultrasound surgery (MRgFUS) | • Non-invasive technique • Uses mechanical energy of focused ultrasound waves to generate precise thermal energy. • Raises tissue temperature to >55 °C with resultant coagulative necrosis and precise tissue ablation margins. | • Performed under MRI guidance to monitor ablation in real-time • Transrectal approach • Patient under general anesthesia or deep sedation, in low lithotomy position on a modified MRI table. • Foley or suprapubic catheter for continuous bladder drainage • Endorectal treatment probe and balloon filled with degassed water for rectal and device cooling | Indications: Localized intermediate-risk prostate cancer suitable for focal therapy Contraindications: Any contraindication to MRI; Tumors >4–6 cm from the rectal wall; Calcifications adjacent to rectum or in the treatment beam path | Strengths: Precise targeting with MRI guidance; real-time temperature feedback; immediate post-treatment assessment with contrast-enhanced MRI Limitations: Limited access to anterior gland lesions; Calcifications in beam path may impede treatment; procedural length and additional costs compared to US-guided HIFU | Ehdaie et al. [22] Ghai et al. [24] | Phase II studies completed; FDA approval |
Transurethral ultrasound ablation (TULSA) | • Minimally invasive procedure • Delivers high-intensity directional ultrasound energy to produce ablative temperatures • Raises tissue temperature to >55 °C with resultant coagulative necrosis and precise tissue ablation margins. | • Performed under MRI guidance to monitor ablation in real-time • Transurethral approach • Patient under general anesthesia or deep sedation • Ultrasound applicator is inserted into the prostatic urethra; rectal and urethral cooling to protect surrounding tissues | Indications: Intermediate-risk prostate cancer; subtotal gland ablation Contraindications: Any contraindication to MRI; Urethral stricture or inability to place the urethral device | Strengths: MRI guidance enhances precision and safety; Real-time thermometry and feedback control for consistent ablation; immediate post-treatment assessment with contrast-enhanced MRI; Able to treat anterior lesions Limitations: Risk of urethral injury or stricture due to rigid applicator; potential for residual cancer in the presence of calcifications in beam path; increased procedure time, complexity, and cost due to MRI guidance | Klotz et al. [32] Chin et al. [29] | Phase II studies completed; FDA approval |
Focal laser ablation (FLA) | ||||||
MRI-guided FLA | • Requires interstitial placement of diode lasers • Delivers electromagnetic radiation (700–1064 nm) in the form of coherent light, typically in the near- infrared spectrum • Heat from the laser induces protein denaturation and coagulative necrosis | • MRI-guided for real-time lesion targeting and temperature monitoring • Transperineal or transrectal approach | Indications: localized, intermediate-risk prostate cancer Contraindications: large tumors may limit use | Strengths: Precise targeting with MRI guidance; real-time temperature feedback for precise control of ablation temperatures; minimizes damage to surrounding tissue Limitations: Forms cylindrical ablation zones with diameters <15 mm, requiring multiple applicators for adequate coverage; Increased procedure time, cost, and complexity due to MRI guidance | Eggener et al. [42] Walser et al. [45] | Phase II with FDA approval for soft tissue ablation |
Ultrasound-guided FLA | • Requires interstitial placement of diode lasers • Delivers electromagnetic radiation (700–1064 nm) in the form of coherent light, typically in the near- infrared spectrum • Heat from the laser induces protein denaturation and coagulative necrosis | • Guided by ultrasound or MRI-TRUS fusion for lesion localization • Transperineal or transrectal approach | Indications: Localized, intermediate-risk prostate cancer Contraindications: large tumors may limit use | Strengths: Shorter procedure times compared to MRI guidance; reduces resource utilization and costs; easier to perform and more widely accessible given ultrasound-guidance Limitations: Forms cylindrical ablation zones with diameters <15 mm, requiring multiple applicators for adequate coverage; Less precise than MRI-guided techniques as relies on cognitive or software fusion for targeting | Van Riel et al. [50] | Phase I safety and efficacy study |
Histotripsy | • Non-invasive pulsed High-Intensity Focused Ultrasound (HIFU) to induce non-thermal mechanical ablation of tissue • Shock waves lead to bubble activity at the focal point, breaking tissue into subcellular components Employs two methods: • Cavitation cloud histotripsy: High peak negative pressure, dense cavitation bubble clouds • Boiling histotripsy: Shock-induced heating generates vapor bubbles at the focal point | • Transrectal approach via ultrasound imaging. • Non-invasive; does not require transperineal or transurethral access • Enables real-time ultrasound monitoring for treatment feedback | Indications: Potential for treating localized prostate cancer; Applicable in both benign and malignant prostate tissue Contraindications: Not yet validated for large tumors; requires further research in clinical trials to establish safe guidelines | Strengths: non-thermal energy source mitigates heat-sink effects or tissue perfusion challenges; tissue selectivity to spare extracellular structures and minimize damage to surrounding structures; real-time ultrasound-based monitoring Limitations: Primarily at the preclinical stage with limited human trials | Schade et al. [72] Rosnitskiy et al. [15] | Preclinical stage |
