Dynamic contrast enhanced CT measurement of blood flow during interstitial laser photocoagulation: comparison with an Arrhenius damage model

Morphologic changes of mammary carcinomas in mice over time as monitored by flat-panel detector volume computed tomography

Noninvasive methods are strongly needed to detect and quantify not only tumor growth in murine tumor models but also the development of vascularization and necrosis within tumors. This study investigates the use of a new imaging technique, flat-panel detector volume computed tomography (fpVCT), to monitor in vivo tumor progression and structural changes within tumors of two murine carcinoma models. After tumor cell inoculation, single fpVCT scans of the entire mice were performed at different time points. The acquired isotropic, high-resolution volume data sets enable an accurate real-time assessment and precise measurements of tumor volumes. Spreading of contrast agent-containing blood vessels around and within the tumors was clearly visible over time. Furthermore, fpVCT permits the identification of differences in the uptake of contrast media within tumors, thus delineating necrosis, tumor tissues, and blood vessels. Classification of tumor tissues based on the decomposition of the underlying mixture distribution of tissue-related Hounsfield units allowed the quantitative acquisition of necrotic tissues at each time point. Morphologic alterations of the tumor depicted by fpVCT were confirmed by histopathologic examination. Concluding, our data show that fpVCT may be highly suitable for the noninvasive evaluation of tumor responses to anticancer therapies during the course of the disease.

Interstitial microwave thermal therapy for prostate cancer

Thermal therapy is used to kill tumors by heating them to temperatures >50 degrees C for an extended period of time. Cell death results from thermal coagulation. The energy sources available for this approach include radiofrequency electrodes, microwave antennas, laser fiberoptics, and ultrasound transducers. Each of these modalities has the potential to be delivered in a minimally invasive manner, and many theoretical and experimental investigations of these devices have been performed. This review describes current knowledge of interstitial microwave thermal therapy for prostate cancer. Examples are given from an ongoing trial in patients who have recurrent or persistent disease following radiation therapy. Future directions for pretreatment planning and real-time monitoring and control are discussed. These techniques have the potential to optimize treatments on a patient-specific basis and will be instrumental in planned future trials of this therapy as first line for prostate cancer.

Models and measurements of light intensity changes during laser interstitial thermal therapy: implications for optical monitoring of the coagulation boundary location

We have developed a multi-region spherical Monte Carlo (MC) model to simulate the dynamic changes in light intensity measured during laser interstitial thermal therapy (LITT). Model predictions were validated experimentally in tissue-simulating albumen phantoms with well-characterized optical properties that vary dynamically with LITT in a way similar to tissue. For long treatments (2.5 W, approximately 1800 s), the transient light intensity changes demonstrated better qualitative agreement with a three-region MC model (with an inner layer of fully coagulated optical properties, a middle layer of partially coagulated properties and an outer region of native properties); for short treatments (4 W, approximately 240 s), better qualitative agreement was seen with a two-region MC model (with an inner layer of fully coagulated properties and outer region of native properties). These differences were attributed to differences in coagulation formation during low- and high-powered heating regimes, respectively. At the end of heating, a three-region coagulation zone was observed for both heating schemes. Quantitatively, final light intensity changes at the end of heating were compared with changes predicted by both two- and three-region MC for the same experimentally measured coagulation size and found to agree within approximately 30% for both models. The developed MC model helps lend insight into the nature of thermal coagulation events occurring for low and high power LITT irradiation schemes.

Ultrasound properties of human prostate tissue during heating

Changes in the ultrasound (US) properties of tissue during heating affect the delivery of US thermal therapy and may provide a basis for US image monitoring of thermal therapy. The US attenuation coefficient and backscatter power of fresh human prostate tissue were measured as the tissue was heated. Samples of human prostate were obtained directly from autopsies and heated rapidly to final temperatures of 45 degrees C, 50 degrees C, 55 degrees C, 60 degrees C and 65 degrees C. A 5.0-MHz transducer was scanned in a raster pattern over the tissue and radiofrequency (RF) data were collected at 36 uncorrelated positions. Both attenuation and backscatter were measured over the frequency range 3.5 to 7.0 MHz at each min of a 30-min heating. Little change was observed in attenuation or backscatter at 55 degrees C or less. The attenuation coefficient and backscatter power increased by factors of 1.25 and 5, respectively, during the 60 degrees C heating. During the 65 degrees C heating, the same properties showed increases by factors of 2.7 and 9.

Interstitial microwave thermal therapy for prostate cancer: method of treatment and results of a phase I/II trial

PURPOSE

Interstitial microwave thermal therapy is experimental treatment for prostate cancer with the goal of curing disease, while causing fewer complications than standard treatment options. We present a method for delivering interstitial microwave thermal therapy using microwave radiating helical antennae inserted percutaneously under transrectal ultrasound guidance. We report the results of a trial of this method in 25 patients in whom primary external beam radiation therapy had previously failed. This patient group currently has limited curative options that are associated with a high complication rate. However, these recurrent tumors often remain localized to the prostate, and so they may be amenable to localized therapy.

MATERIALS AND METHODS

Patients with proved prostatic adenocarcinoma were candidates for treatment when prostate specific antigen (PSA) was 15 ng./ml. or less and prostate volume was 50 cc. or less. Followup included PSA measurement, digital rectal examination, urinalysis, and documentation of adverse events at 4, 8, 12 and 24 weeks. Sextant biopsy was performed at week 24. The procedure involved the insertion of 5 antennae percutaneously through a modified brachytherapy template. The antenna arrangement was determined based on computer simulated predictions of temperature throughout the prostate. The prostate was dissected away from the rectum by an injection of sterile saline to provide a thermal barrier that protected the rectum from thermal damage. Temperatures were monitored using interstitial mapping thermistor probes that were also inserted through the template. A minimum peripheral target temperature of 55C but less than 70C was maintained for 15 to 20 minutes, while the urethra, rectum and hydrodissection space remained below 42C. The urethra and rectum were actively cooled in addition to hydrodissection.

RESULTS

Peripheral target temperatures of 55C were achieved. The urethra and rectum remained at a safe temperature. The procedure, including setup and treatment, required approximately 2.5 hours of operating room time. At 24 weeks the PSA nadir was 0.5 ng./ml. or less in 52% of patients and 0.51 to 4 ng./ml. was achieved in an additional 40%. The negative biopsy rate at 24 weeks was 64%, assuming that 3 patients lost to followup would have had positive results. No major complications were observed and in most cases minor complications resolved within 3 months.

CONCLUSIONS

Interstitial microwave thermal therapy for prostate cancer was developed to heat the prostate safely to a cytotoxic temperature. Experience with 25 patients in whom external beam radiation therapy for prostate cancer had failed indicates that the treatment is safe. Although our series indicates that this therapy may be effective, further studies and longer followup are required in larger patient groups to confirm the potential role of this therapy as an option for recurrent and primary prostate cancer.