Energy-based ablative therapy of prostate cancer: high-intensity focused ultrasound and cryoablation

Adaptation of a Clinical High-Frequency Transrectal Ultrasound System for Prostate Photoacoustic Imaging: Implementation and Pre-clinical Demonstration

OBJECTIVE

High-frequency, high-resolution transrectal micro-ultrasound (micro-US: ≥15 MHz) imaging of the prostate is emerging as a beneficial tool for scoring disease risk and accurately targeting biopsies. Adding photoacoustic (PA) imaging to visualize abnormal vascularization and accumulation of contrast agents in tumors has potential for guiding focal therapies. In this work, we describe a new imaging platform that combines a transrectal micro-US system with transurethral light delivery for PA imaging.

METHODS

A clinical transrectal micro-US system was adapted to acquire PA images synchronous to a tunable laser pulse. A transurethral side-firing optical fiber was developed for light delivery. A polyvinyl chloride (PVC)-plastisol phantom was developed and characterized to image PA contrast agents in wall-less channels. After resolution measurement in water, PA imaging was demonstrated in phantom channels with dyes and biodegradable nanoparticle contrast agents called porphysomes. In vivo imaging of a tumor model was performed, with porphysomes administered intravenously.

RESULTS

Photoacoustic imaging data were acquired at 5 Hz, and image reconstruction was performed offline. PA image resolution at a 14-mm depth was 74 and 261 μm in the axial and lateral directions, respectively. The speed of sound in PVC-plastisol was 1383 m/s, and the attenuation was 4 dB/mm at 20 MHz. PA signal from porphysomes was spectrally unmixed from blood signals in the tumor, and a signal increase was observed 3 h after porphysome injection.

CONCLUSION

A combined transrectal micro-US and PA imaging system was developed and characterized, and in vivo imaging demonstrated. High-resolution PA imaging may provide valuable additional information for diagnostic and therapeutic applications in the prostate.

Diffuse optical tomography to monitor the photocoagulation front during interstitial photothermal therapy: Numerical simulations and measurements in tissue-simulating phantoms

Near-infrared interstitial photothermal therapy (PTT) is currently undergoing clinical trials as an alternative to watchful waiting or radical treatments in patients with low/intermediate-risk focal prostate cancer. Currently, magnetic resonance imaging (MRI)-based thermography is used to monitor thermal energy delivery and determine indirectly the completeness of the target tumor destruction while avoiding damage to adjacent normal tissues, particularly the rectal wall. As an alternative, transrectal diffuse optical tomography (TRDOT) is being developed to image directly the photocoagulation boundary based on the changes in tissue optical properties, particularly scattering. An established diffusion-theory finite-element software platform was used to perform forward simulations to determine the sensitivity of changes in the optical signal resulting from a growing coagulated lesion with optical scattering contrast, for varying light source-detector separations in both longitudinal and transverse imaging geometries. The simulations were validated experimentally in tissue-simulating phantoms using an existing continuous-wave TRDOT system, in a configuration that is representative of one potential intended clinical use. This provides critical guidance for the optimum design of the transrectal applicator probe, in terms of achieving maximum sensitivity to the presence of the coagulation boundary and, consequently, the highest accuracy in determining the boundary location relative to the rectal wall.

Thermostability of biological systems: fundamentals, challenges, and quantification

This review examines the fundamentals and challenges in engineering/understanding the thermostability of biological systems over a wide temperature range (from the cryogenic to hyperthermic regimen). Applications of the bio-thermostability engineering to either destroy unwanted or stabilize useful biologicals for the treatment of diseases in modern medicine are first introduced. Studies on the biological responses to cryogenic and hyperthermic temperatures for the various applications are reviewed to understand the mechanism of thermal (both cryo and hyperthermic) injury and its quantification at the molecular, cellular and tissue/organ levels. Methods for quantifying the thermophysical processes of the various applications are then summarized accounting for the effect of blood perfusion, metabolism, water transport across cell plasma membrane, and phase transition (both equilibrium and non-equilibrium such as ice formation and glass transition) of water. The review concludes with a summary of the status quo and future perspectives in engineering the thermostability of biological systems.

Nanoparticle-mediated thermal therapy: evolving strategies for prostate cancer therapy

PURPOSE

Recent advances in nanotechnology have resulted in the manufacture of a plethora of nanoparticles of different sizes, shapes, core physicochemical properties and surface modifications that are being investigated for potential medical applications, particularly for the treatment of cancer. This review focuses on the therapeutic use of customised gold nanoparticles, magnetic nanoparticles and carbon nanotubes that efficiently generate heat upon electromagnetic (light and magnetic fields) stimulation after direct injection into tumours or preferential accumulation in tumours following systemic administration. This review will also focus on the evolving strategies to improve the therapeutic index of prostate cancer treatment using nanoparticle-mediated hyperthermia.

CONCLUSIONS

Nanoparticle-mediated thermal therapy is a new and minimally invasive tool in the armamentarium for the treatment of cancers. Unique challenges posed by this form of hyperthermia include the non-target biodistribution of nanoparticles in the reticuloendothelial system when administered systemically, the inability to visualise or quantify the global concentration and spatial distribution of these particles within tumours, the lack of standardised thermal modelling and dosimetry algorithms, and the concerns regarding their biocompatibility. Nevertheless, novel particle compositions, geometries, activation strategies, targeting techniques, payload delivery strategies, and radiation dose enhancement concepts are unique attributes of this form of hyperthermia that warrant further exploration. Capitalising on these opportunities and overcoming these challenges offers the possibility of seamless and logical translation of this nanoparticle-mediated hyperthermia paradigm from the bench to the bedside.

Transanorectal interventions

Over the past few decades, advances in modern imaging technology have enabled less invasive approaches to diagnose and treat disease. In the field of image-guided techniques, this has seen the common adaptation of needle biopsy and catheter drainage into clinical practice. In this article we review the most common applications of transanorectal techniques. As nearly all these techniques are performed under ultrasound guidance in dayto-day practice, the review focuses almost exclusively on ultrasound-enabled techniques.

High-intensity focused ultrasound in prostate cancer; a systematic literature review of the French Association of Urology

We discuss the efficacy and safety of high-intensity focused ultrasound (HIFU) in patients with prostate cancer, to define the best indications for HIFU in daily clinical practice as primary therapy. We searched Medline and Embase for clinical studies evaluating the efficacy and safety of HIFU in prostate cancer (July 2007), and abstracts presented at the 2005-2007 annual meetings of the European Association of Urology and American Urological Association were screened. In all, 37 articles/abstracts were selected. As the data on HIFU as salvage therapy were limited, we focused on HIFU as primary therapy. Studies consisted of case series only. Included patients were approximately 70 years old with T1-T2 N0M0 disease, Gleason Score <or=7, a prostate-specific antigen (PSA) level of <or=28 ng/mL and a prostate volume of <or=40 mL. Negative biopsy rates with the Ablatherm device (EDAP TMS S.A., Vaulx-en-Velin, France) were 64-93%, and a PSA nadir of <or=0.5 ng/mL was achieved in 55-84% of patients. The 5-year actuarial disease-free survival rates were 60-70%. The most common complications were stress urinary incontinence, urinary tract infection, urethral/bladder neck stenosis or strictures, and erectile dysfunction. For the Ablatherm device, the rate of complications has been significantly reduced over the years, due to technical improvements in the device and the use of transurethral resection of the prostate before HIFU. In conclusion, HIFU as primary therapy for prostate cancer is indicated in older patients (>or=70 years) with T1-T2 N0M0 disease, a Gleason score of <7, a PSA level of <15 ng/mL and a prostate volume of <40 mL. In these patients HIFU achieves short-term cancer control, as shown by a high percentage of negative biopsies and significantly reduced PSA levels. The median-term survival data also seem promising, but long-term follow-up studies are needed to further evaluate cancer-specific and overall survival rates before the indications for primary therapy can be expanded.