Volume 34, Issue 6, June 2007
Index of content:
- Joint Imaging — Therapy Symposium: Room M100J
- Image‐guided Alternative Therapies
34(2007); http://dx.doi.org/10.1118/1.2761503View Description Hide Description
HIFU has long been known to offer the potential of very precise “Trackless lesioning” but has only recently with the current high quality methods of medical imaging, become a practical possibility for clinical treatment.
Focused ultrasound uses ultrasound energy for tissue ablation. When the sound waves are focused to a small volume in the body, the intensity is high and the temperature at the focal point rises to 70–95°C, high enough to ablate the tissue. Proper treatment design will ensure that the energy density will be high at the focal point but low at other locations, and thus avoiding damages to nearby normal tissues.
The volume of ablation (lesion) following a single HIFU exposure is small and will vary according to transducer characteristics, but it is typically cigar shaped with dimensions in the order of 1–3 mm (transverse) × 8–15 mm (along the beam axis). To ablate clinically relevant volumes these lesions must be placed side by side systematically to “paint out” the target tumor.
Simply calculating an optimal treatment plan is not enough to ensure optimal outcome. Patient anatomic variability and tissue inhomogeneities have been shown to produce vastly different responses to thermal energy deposition, especially deep in the body. High quality imaging techniques can provide precise visualization and localization of the tissue damage. MR images enable the physician to localize the tumor and plan the treatment in the full 3 dimensions. Real‐time MR thermometry can provide an indication of tissue damage if critical temperatures are known.
In several centers worldwide, HIFU is now being used clinically to treatment solid tumors (both malignant and benign), including those of the brain, breast, liver, kidney, prostate, bone matastases, pancreas and soft‐tissue sarcoma. The MRgFUS unit is currently available for clinical applications.
This lecture will provide an overview of MrgFU and introduce the equipment that is commercially available for clinical applications in cancer treatment.
1. The principles of MRgFUS.
2. Advantages and limitations of MRgFUS for tissue ablation.
3. Potential clinical applications of MRgFUS for cancer treatment.
34(2007); http://dx.doi.org/10.1118/1.2761504View Description Hide Description
Purpose: This study analyzes the results of image‐guided prostate photodynamic therapy(PDT) that integrates PDTdosimetry, light source optimization, computerized light power adjustment, and volumetric real‐time light fluence calculation to deliver uniform photodynamic dose to the target volume (prostate) and spares the critical structures (rectum and bladder). Methods and Materials: All procedures are under the image guidance of transrectal ultrasound. The PDTdosimetry includes multi‐channel real‐time in‐vivo light dosimetry,absorption and fluorescence spectroscopy for 3D optical properties, drug concentrations, and tissue oxygenation. Drug concentration is also determined using fluorescence from a single optical fiber. These measurements are made before and after motexafin lutetium (MLu)‐mediated photodynamic therapy(PDT) using a computerized step motor. The light fluence rate distributions are also measured along the catheters during PDT and compared to the 3D volumetric light fluence calculations. Real‐time light fluence calculation was performed on the 3D target volumes using ultrasoundimage guidance. An optimization algorithm determines the light source strength, lengths, location, and retraction for cylindrical diffusing fibers (CDF) based on the 3D heterogeneous optical properties. The resulting light source power is feedback into a 12‐channel beamsplitter that is connected to a motorized attenuator system to control the light source intensity interactively during PDT.Results: Preliminary data have shown widespread heterogeneities of optical properties and photosensitizing drug distribution. As a result of these heterogeneities, methods to quantifying the three‐dimensional (3D) distributions of these quantities in individual prostate are essential for the successful application of PDT. Comparison of light fluence rate between real‐time measurements and calculation is performed in heterogeneous medium and the standard deviations are within 30% with a simplified model and better than 11% for an improved model. Conclusions: We have shown the rational and potential for an integrated system that is capable of obtaining critical parameters (light, drug, and oxygenation) and using the PDTdosimetry result as feedback to optimize treatment delivery. We concluded that a real‐time dosimetry and feedback system for monitoring PDT dose during treatment is both achievable and required for clinical interstitial PDT applications.
1. To explain the basic principle of PDTdosimetry.
2. To review explicit PDTdosimetry techniques to characterize tissue optical properties, drug concentration, tissue oxygen concentration, and PDT efficacy.
3. To discuss the rational and requirement for a feedback system incorporating PDTdosimetry,PDT dose optimization, and computerized light delivery.
4. Summarize the clinical results of Prostate PDT.
34(2007); http://dx.doi.org/10.1118/1.2761505View Description Hide Description
Cryoablation: Scientific Foundation, Treatment Planning and Clinical Practice.
Interest in and utilization of cryoablation as a primary therapy for many types of cancer has increased markedly in the past decade. The procedure has evolved significantly from a technology perspective with engineering advances yielding greater control of ice formation within the body as well as enhanced visualization. This, coupled with isotherm modeling and treatment planning, has resulted in the ability to accurately target tissue for cryoablation. The organ to which these advances are most often applied is the prostate. This is due to the prostate being a relatively difficult structure to treat. The passage of the urethra through the gland necessitates the use of multiple cryoprobes and the procedure is confounded by the sensitivity of adjacent structures including the neurovascular bundles, external sphincter and rectum. Even with these obstacles, modern prostate cryoablation has emerged both as a primary prostate cancertreatment option and as a salvage therapy following failed radiation therapy.
This lecture will review the fundamentals of cryobiology and the seminal work which established clinical endpoints. The technological basis of the procedure will be discussed including both fundamentals of cryoprobe design and compatibility imaging modalities. Lastly, clinical outcomes of the prostate cryoablation will be compared to radical prostatectomy (the gold standard), external beam radiation therapy, brachytherapy and IMRT.
1. Understand the damage mechanisms of cryoablation and how they differ from radiation damage.
2. Understand the fundamentals of how prostate cryoablation is performed and the technologies used to do so, and
3. Understand how the outcomes of cryoablation compare to other treatment modalities.
34(2007); http://dx.doi.org/10.1118/1.2761506View Description Hide Description