Transrectal microwave hyperthermia for advanced prostate cancer: long-term clinical results

Investigation of the use of microwave ablation with and without cooling urethral perfusion for thermal ablation of the prostate gland in canine cadavers

OBJECTIVE

To investigate the use of microwave ablation (MWA) with cooling urethral perfusion and with no perfusion (MWA-UP and MWA-NP, respectively) for prostate gland ablation in canine cadavers.

ANIMALS

Cadavers of 18 sexually intact male dogs.

PROCEDURES

After technique refinement in 2 cadavers, laparotomy with ultrasound-guided MWA-UP (n = 8) or MWA-NP (8) of the prostate gland was performed in 16 cadavers. Normograde cystourethroscopy was performed before and after treatment; recorded images were reviewed in a blinded manner for scoring of urethral mucosal discoloration and loss of integrity. Difficulty with cystoscope insertion was recorded if present. Excised prostate glands were fixed for serial sectioning, gross measurements, and calculation of percentage ablation. Percentages of prostate tissue necrosis from MWA, denuded urethral mucosa, and depth of epithelial surface loss in an adjacent section of the colon were estimated histologically. Variables of interest were statistically analyzed.

RESULTS

Difficulty with cystoscope insertion after treatment was significantly more common and scores for urethral mucosal discoloration and loss of integrity were significantly higher (indicating more severe lesions) for the MWA-NP group than for the MWA-UP group. The histologically assessed percentage of denuded urethral mucosa was also greater for the MWA-NP group. Overall median percentage prostate gland ablation was 73%; this result was not associated with prostate gland volume or chronological order of treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

MWA-UP induced subtotal thermal necrosis of prostate glands in canine cadavers while limiting urethral mucosal injury. Further study is required to optimize the technique and evaluate its safety and efficacy in vivo as a future curative-intent treatment for prostatic tumors in dogs.

Computational modelling of microwave tumour ablations

Microwave tissue heating is being increasingly utilised in several medical applications, including focal tumour ablation, cardiac ablation, haemostasis and resection assistance. Computational modelling of microwave ablations is a precise and repeatable technique that can assist with microwave system design, treatment planning and procedural analysis. Advances in coupling temperature and water content to electrical and thermal properties, along with tissue contraction, have led to increasingly accurate computational models. Developments in experimental validation have led to broader acceptability and applicability of these newer models. This review will discuss the basic theory, current trends and future direction of computational modelling of microwave ablations.

In vitrothermal therapy of AT-1 Dunning prostate tumours

To advance the utility of prostate thermal therapy, this study investigated the thermal thresholds (temperature-time) for prostate tissue destruction in vitro. The AT-1 Dunning prostate tumour model was chosen for the study. Three hundred micron thick sections were subjected to controlled temperature-time heating, which ranged from low (40 degrees C, 15 min) to high thermal exposures (70 degrees C, 2 min) (n = 6). After subsequent tissue culture at 37 degrees C, the sections were evaluated for tissue injury at 3, 24 and 72 h by two independent methods: histology and dye uptake. A graded increase in injury was identified between the low and high thermal exposures. Maximum histologic injury occurred above 70 degrees C, 1 min with >95% of the tissue area undergoing significant cell injury and coagulative necrosis. The control and 40 degrees C, 15 min sections showed histologic evidence of apoptosis following 24 and 72 h in culture. Similar signs of apoptosis were minimal or absent at higher thermal histories. Vital-dye uptake quantitatively confirmed complete cell death after 70 degrees C, 2 min. Using the dye data, Arrhenius analysis showed an apparent breakpoint at 50 degrees C, with activation energies of 135.8 kcal/mole below and 4.7 kcal/mole above the threshold after 3 h in culture. These results can be used as a conservative benchmark for thermal injury in the cancerous prostate. Further characterization of the response to thermal therapy in an animal model and in human tissues will be important in establishing the efficacy of the procedure

Repression of thermotolerance in Dunning R3327 prostate carcinoma cells by 2-deoxy-glucose

The transient addition of the cytosolic energy depletor 2-deoxy-glucose to cultures of rat prostate carcinoma cells blunted the induction of Hsp70 protein following exposure to elevated temperatures in a manner that appeared to parallel its effects on energy metabolism. While the reduction in stress-induced heat-shock protein expression by treatment with 2-deoxy-glucose had no effects on the acute loss of cellular viability after exposure to heat, the acquisition of thermotolerance in response to a conditioning stimulus was specifically repressed. Therefore, 2-deoxy-glucose will be a useful tool in the investigation of mechanisms that mediate immediate versus chronic responses to cellular stress, including the specific roles played by members of the heat-shock protein family of proteins. These results might have important implications in the design of protocols for the hyperthermic treatment of tumours.

Application of External Microwave Thermotherapy in Urology: Past, Present, and Future

The excellent clinical results of transurethral microwave thermotherapy (TUMT) for the treatment of symptomatic benign prostatic hyperplasia (BPH) gave to TUMT the leading position among the microwave thermotherapy modalities available for the treatment of different urologic conditions. Research in TUMT has focused on operating software, temperature monitoring, intraprostatic heat distribution, cell-kill calculations, and correlations with clinical variables. Randomized comparisons of TUMT with other established therapies for BPH, including transurethral resection, have facilitated the evaluation of the clinical outcome, durability, morbidity, and costs of the treatment. The applications of microwave thermotherapy in other urologic diseases are also presented in this review.

Minimally invasive management of the small renal tumor: review of laparoscopic partial nephrectomy and ablative techniques

The most profound change among the many that have occurred in the management of renal-cell carcinoma (RCC) in recent years is the advent of nephron-sparing surgery for masses <4 cm. The main challenge now is to reduce the morbidity associated with such procedures. Because of the problems in obtaining hemostasis, only a few highly experienced surgeons are performing partial nephrectomy laparoscopically. Numerous techniques and tools have been studied, including laparoscopic duplication of the open operation; hand-assisted surgery; double-loop and cable-tie tourniquets; ultrasonic shears; radiofrequency, microwave, and laser energy; the Endosnare; and hydro-jet dissection. Also, ablation with cold, radiofrequency energy, or high-intensity focused ultrasound is being explored. Just as open surgery for urolithiasis has been all but replaced by extracorporeal lithotripsy and endoscopic techniques, treatment of most RCCs will ultimately shift from open to minimally invasive methods.

Laser-induced hyperthermia in rat prostate cancer: role of site of tumor implantation

OBJECTIVES

To investigate the importance of the site of tumor implantation on the treatment response to laser-induced hyperthermia (LIH) of rat prostate cancer (PCa), because interventional manipulations of PCa have been reported to increase metastatic dissemination.

METHODS

Seven to nine days after either subcutaneous or orthotopic implantation of MatLyLu cells, LIH (46.5 degrees C) was induced using pulsed irradiations of a neodymium:yttrium-aluminum-garnet laser. Both local control and distant metastases were evaluated. Plasma metalloproteinase 9 (MMP-9) was tested as a possible marker of PCa progression and LIH response.

RESULTS

Twelve days after LIH treatment of subcutaneous tumors, the volumes were reduced by 64% after 8 minutes of irradiation, 73% after 10 minutes, 81% after 15 minutes, and 91.1% after 20 minutes. In the orthotopic model, the corresponding tumor reductions were 44% after 10 minutes, 61% after 20 minutes, and 65% after 30 minutes. Lung metastases were observed in only 1 animal with subcutaneous tumors. In contrast, 86% of the orthotopic tumor-bearing animals treated for 30 minutes had lung metastases compared with 23% of the untreated tumor-bearing rats. MMP-9 expression was detected in both orthotopic and subcutaneous tumor tissue and in the plasma of tumor-bearing rats. The prostate tissue of healthy rats and subcutaneous tumor-bearing rats was devoid of MMP-9. The plasma levels of MMP-9 showed a trend toward direct correlation with local tumor control but no correlation with the incidence of metastasis.

CONCLUSIONS

These data emphasize the importance of the site of tumor implantation for evaluation of the efficacy of therapeutic interventions and may warrant further studies before widespread clinical application of LIH as monotherapy.

Transurethral balloon laser enhanced thermotherapy in the canine prostate

BACKGROUND AND OBJECTIVE

Hyperthermia is performed for prostate cancer. We examined the selective induction of coagulonecrotic changes in the objective area of the canine prostate in enhancing the effect of hyperthermia and treating the target area with transurethral balloon laser enhanced thermotherapy (TUBAL-ET) using a light absorbent material.

STUDY DESIGN/MATERIALS AND METHODS

The heat exchange of ultrafine carbon particles after laser irradiation was observed in a phantom study using thermography. The carbon solution was injected at the right prostatic lobe in dogs and TUBAL-ET was performed.

RESULTS

The charcoal absorbed the Nd:YAG laser energy and apparently converted it into thermal energy in the phantom study by thermographic observation. TUBAL-ET induced coagulonecrotic changes only at the area at which carbon had been injected in the prostate gland. The necrotic tissue was almost absorbed at four weeks after treatment.

CONCLUSIONS

TUBAL-ET induces tissue damage at the target area in the prostate gland.

Supraphysiological thermal injury in Dunning AT-1 prostate tumor cells

To investigate the potential application of thermal therapy in the treatment of prostate cancer, the effects of supraphysiological temperatures (40-70 degrees C) for clinically relevant time periods (approximately 15 minutes) were experimentally studied on attached Dunning AT-1 rat prostate cancer cells using multiple assays. The membrane and reproductive machinery were the targets of injury selected for this study. In order to assess membrane injury, the leakage of calcein was measured dynamically, and the uptake of PI was measured postheating (1-3 hours). Clonogenicity was used as a measure of injury to the reproductive machinery 7 days post-injury after comparable thermal insults. Experimental results from all three assays show a broad trend of increasing injury with an increase in temperature and time of insult. Membrane injury, as measured by the fluorescent dye assays, does not correlate with clonogenic survival for many of the thermal histories investigated. In particular, the calcein assay at temperatures of < or = 40 degrees C led to measurable injury accumulation (dye leakage), which was considered sublethal, as shown by significant survival for comparable insult in the clonogenic assay. Additionally, the PI uptake assay used to measure injury post-thermal insult shows that membrane injury continues to accumulate after thermal insult at temperatures > or = 50 degrees C and may not always correlate with clonogenicity at hyperthermic temperatures such as 45 degrees C. Last, although the clonogenic assay yields the most accurate cell survival data, it is difficult to acquire these data at temperatures > or = 50 degrees C because the thermal transients in the experimental setup are significant as compared to the time scale of the experiment. To improve prediction and understanding of thermal injury in this prostate cancer cell line, a first-order rate process model of injury accumulation (the Arrhenius model) was fit to the experimental results. The activation energy (E) obtained using the Arrhenius model for an injury criterion of 30 percent for all three assays revealed that the mechanism of thermal injury measured is likely different for each of the three assays: clonogenics (526.39 kJ/mole), PI (244.8 kJ/mole), and calcein (81.33 kJ/mole). Moreover, the sensitivity of the rate of injury accumulation (d omega/dt) to temperature was highest for the clonogenic assay, lowest for calcein leakage, and intermediate for PI uptake, indicating the strong influence of E value on d omega/dt. Since the clonogenic assay is linked to the ultimate survival of the cell and accounts for all lethal mechanisms of cellular injury, the E and A values obtained from clonogenic study are the best values to apply to predict thermal injury in cells. For higher temperatures (> or = 50 degrees C) indicative of thermal therapies, the results of PI uptake can be used as a conservative estimate of cell death (underprediction). This is useful until better experimental protocols are available to account for thermal transients at high temperature to assess clonogenic ability. These results provide further insights into the mechanisms of thermal injury in single cell systems and may be useful for designing optimal protocols for clinical thermal therapy.

Prostate cancer: MR imaging and thermometry during microwave thermal ablation-initial experience

Percutaneous interstitial microwave thermoablation of locally recurrent prostate carcinoma was continually guided with magnetic resonance (MR) imaging. Phase images and data were obtained with a rapid gradient-echo technique and were used to derive tissue temperature change on the basis of proton-resonance shift. Thermally devitalized regions correlated well with the phase image findings. MR imaging-derived temperatures were linearly related to the fluoroptic tissue temperatures. MR imaging can be used to guide thermoablation.

Interstitial microwave thermoablation for localized prostate cancer

The conventional treatment for localized prostate cancer can be associated with significant morbidity and cost. Interstitial microwave thermoablation is a minimally invasive procedure used experimentally to treat selected patients with failed radiation therapy of prostate cancer at our institution. Preliminary results in these patients suggest that this treatment might be a useful alternative in selected patients with previously untreated localized prostate cancer. In this report we describe the first use of percutaneous transperineal interstitial microwave thermoablation to treat a case of primary prostate cancer. There were no treatment complications. At 18 months the patient's serum prostate-specific antigen remains undetectable, and his prostate biopsy shows no evidence of malignancy. These very preliminary but exciting results in this single patient suggest that this experimental technique should be explored further.

Heat-induced changes in the mechanics of a collagenous tissue: isothermal free shrinkage

We present data from isothermal free-shrinkage tests (i.e., performed in the absence of mechanical loads) wherein bovine chordae tendineae were subjected to temperatures from 65 to 85 degrees C for 120 to 1200 s. These data reveal four new insights into heat-induced denaturation of a collagenous tissue. First, a characteristic time for the free shrinkage appears to exhibit an Arrhenius-type relationship with temperature. Second, scaling the actual heating time via the characteristic time results in a single correlation between free shrinkage and the duration of heating; this correlation suggests a time-temperature equivalence. Third, it is the cumulative, not current, heating time that governs the free shrinkage. And fourth, heat-induced free shrinkage is partially recovered when the tissue is returned to 37 degrees C, this recovery also being time-dependent. Although these findings will help guide future experimentation and constitutive modeling, as well as the design of new heat-based clinical therapies, there is a pressing need to collect additional isothermal data, particularly in the presence of well-defined mechanical loads.

Beta-galactosidase as a marker of HSP70 promoter induction in Dunning R3327 prostate carcinoma cells

Hyperthermia is known to improve the response of tumors to radiation or chemotherapeutic treatment when combined in multimodal strategies. The cellular response to hyperthermia is associated with the synthesis of heat shock proteins (HSP). To study the stress response in prostate cancer we have developed a clone of Dunning R3327 rat prostate carcinoma cells stably transfected with a gene construct containing the E. coli beta-galactosidase gene driven by the Drosophila HSP70 promoter. The measurement of beta-galactosidase serves as a rapid and semiquantitative assay of HSP70 gene activation. The Dunning cell clone showed evidence of incorporation of the HSP70/beta-galactosidase construct within the genomic DNA by Southern blot analysis. When compared to mock-transfected control cells, the clone showed minimal baseline beta-galactosidase activity, which significantly increased following a hyperthermic stress. The time course of beta-galactosidase elevation following heat stress paralleled the time course of cellular HSP70 elevation by Western blot analysis. These stably transfected Dunning R3327 cells may provide a useful tool to study the effects of hyperthermia, radiation, and chemotherapeutic agents on the cellular stress response and in the establishment of HSP70 as a marker of cellular resistance in the multimodal treatment of prostate cancer.

Hyperthermia inhibits proliferation and stimulates the expression of differentiation markers in cultured thyroid carcinoma cells

In the last two decades hyperthermia has increasingly been used as adjuvant therapy for the treatment of malignant tumours. The effects of heat were therefore analysed on cultured thyroid epithelial cells from patients with thyroid cancer and from non-malignant control thyroids. Purified thyroid cells were subjected to heat treatment (42.5 degrees C; 90 min). After 24 h [3H]thymidine incorporation was assessed and the expression of heat shock protein 72 (hsp72), thyroglobulin, CD54 (ICAM-I) and MHC class-Il were analysed by immunofluorescence staining. Additionally mRNA analysis was performed by Northern blotting. Whereas hyperthermia inhibited the proliferation of thyroid cells, it significantly increased the expression of hsp72, thyroglobulin, CD54 and HLA-DR (P < 0.05). Our results suggest that hyperthermia may suppress growth while supporting differentiation and immune recognition in thyroid cancer. It may therefore be beneficial as a treatment for patients with thyroid carcinoma.

Prostatic UroLume Wallstent for urinary retention due to advanced prostate cancer: a 1-year followup study

We attempt to clarify the long-term clinical reliability of the prostatic UroLume Wallstent in the treatment of urinary retention due to advanced prostate cancer. The stent was placed in 11 stage D prostate cancer patients at high surgical risk and with urinary retention unrelieved by total androgen blockade. At preoperative urethroscopy, the bladder neck and verumontanum were clearly visible and not massively infiltrated by tumor. All patients voided spontaneously at the end of the procedure. At 1 year maximum flow nomograms demonstrated the definite relief of bladder outlet obstruction and of related symptoms in the 10 cases evaluated. As expected, the stent had no evident effect on the natural history of prostate cancer. There were no major complications. Bladder outlet obstruction due to advanced prostate cancer and unrelieved by conventional medical therapy can be treated safely and effectively by the prostatic UroLume Wallstent.

Transrectal microwave hyperthermia for benign prostatic hyperplasia: long-term clinical, pathological and ultrastructural patterns

Transrectal microwave hyperthermia of the prostate was administered to 191 patients with bladder outlet obstruction due to benign prostatic hyperplasia who were either at poor operative risk or who refused surgery. Patients were divided in 2 groups according to age and they underwent either 5 or 10, 60-minute sessions of hyperthermia, with a calculated intraprostatic temperature of 42.5 plus or minus 0.5C. Light and electron microscopy showed no irreversible damage at the glandular epithelium but did demonstrate a significant increase in neoformed intraprostatic capillary-like vessels. At 1, 12 and 24 months residual urine volume was significantly decreased in the majority of patients but only a minor amelioration of urinary flow rates and subjective symptoms was observed. According to maximum flow nomograms all patients were still obstructed postoperatively. Transrectal hyperthermia cannot be considered a genuine alternative to surgery for patients with bladder outlet obstruction due to benign prostatic hyperplasia.