Temperature steering in prostate by simultaneous transurethral and transrectal hyperthermia

Interstitial microwave transition from hyperthermia to ablation: historical perspectives and current trends in thermal therapy

This work reviews the transition from hyperthermia to ablation for cancer treatment with interstitial microwave (MW) antennas. Early work utilising MW energy for thermal treatment of cancer tissue began in the late 1970s using single antennas applied interstitially or the use of multiple interstitial antennas driven with the same phase and equal power at 915 or 2450 MHz. The original antenna designs utilised monopole or dipole configurations. Early work in thermal therapy in the hyperthermia field eventually led to utilisation of these antennas and methods for MW ablation of tumours. Efforts to boost the radiated MW power levels while decreasing antenna shaft temperatures led to incorporation of internally cooled antennas for ablation. To address larger tumours, MW treatment utilised arrays that were simultaneously activated by either non-synchronous or synchronous phase operation, benefiting both hyperthermia and ablation strategies. Numerical modelling was used to provide treatment planning guidance for hyperthermia treatments and is expected to provide a similar benefit for ablation therapy. Although this is primarily a review paper, some new data are included. These new data show that three antennas with 2.5 cm spacing at 45 W/channel and 10 min resulted in a volume of 89.8 cm(3) when operated synchronously, but only 53.4 cm(3) non-synchronously. Efficiency was 1.1 (synchronous) versus 0.7 (non-synchronous). MW systems, treatment planning, and image guidance continue to evolve to provide better tools and options for clinicians and patients in order to provide better approach and targeting optimisation with the goal of improved treatment for the patient.

The position of the opposite flat applicator changes the SAR and thermal distributions of the RF capacitive intracavitary hyperthermia

The variations of the specific absorption rate (SAR) and thermal distribution in the JSHO QA phantoms were investigated by radiofrequency (RF) capacitive intracavitary hyperthermia (ICHT) applicator (AP-T01, Omron Electric Co., Kyoto, Japan) with the changing position of the opposite flat applicator (15-cm in diameter). The thermal distribution was observed with the thermographic camera and the normalized SAR distribution was calculated with the thermal data that were measured with the thermocouple thermometers. The SAR and thermal distributions of AP-T01 significantly varied with the position of the opposite flat applicator. The slope of the normalized SAR became gradual towards the side of the flat applicator. During the operating of a high flow rate (1500 ml/min) cooling system, the region between AP-T01 and the flat applicator was widely and rather homogeneously heated, except the hot spot around the end of AP-T01. This hot spot may be due to the imbalance of cooling of AP-T01 and the warming-up of the electrode. These results suggest that the RF capacitive ICHT using AP-T01 may be clinically effective on the deep-seated tumours in the direction of either the end wall, such as cervical cancers, or the upper wall, such as prostatic cancers and the mediastinal metastatic lymph nodes, if an improvement of the cooling system is achieved.

Detailed interstitial temperature mapping during treatment with a novel transurethral microwave thermoablation system in patients with benign prostatic hyperplasia

PURPOSE

To delineate in detail the temperature changes in the prostate gland and adjacent structures during treatment with a newly designed microwave thermoablation system in patients with benign prostatic hyperplasia (BPH).

MATERIALS AND METHODS

Microwave thermoablation treatment was administered to 22 BPH patients at two centers in the U.S. and Argentina using the Urologix Targis targeted transurethral thermoablation system. Continuous temperature measurements were made with widely spatially dispersed fiber optic thermosensors at 11 to 24 prostatic sites in each patient using a recently described accurate stereotactic method. Urethral and rectal temperatures were also measured.

RESULTS

Treatment using the microwave thermoablation system resulted in marked elevation of intraprostatic temperatures to as high as 80C in some patients with little or no elevation of urethral or rectal temperatures. Average temperature increased with radial distance from the urethra to a peak at 5 to 7 mm. and declined exponentially at greater distances. Higher maximum intraprostatic temperatures in individual patients were associated with a larger zone, up to 24.0 mm. in radius, of prostatic tissue exposed to thermoablative temperatures of 45C and higher. Along the longitudinal axis of the microwave treatment catheter, thermoablative temperatures were confined to a zone of 11.5 mm. from the microwave antenna midpoint apically and 11.3 mm. basally, that is, a range shorter than the length of the treatment catheter's microwave antenna (2.8 to 3.5 cm.). The mean temperature in the posterior sector of the prostate gland during treatment (43.6C; 95% CI, 41.1 to 46.1C) was significantly lower (p < 0.05) by 6.7C than that in the anterolateral prostate (50.3C; 95% CI, 48.3 to 52.3C), as a consequence of the preferential heating design of the treatment catheter. Intraprostatic mean temperature during treatment, as measured at all thermosensor sites without respect to spatial location, was 47.1C (95% CI, 44.2 to 50.0C), a value significantly higher (p < 0.05) than that measured in the urethra (39.6C; 95% CI, 36.6 to 42.6C) or rectum (37.7C; 95% CI, 36.7 to 38.7C). There was a strong correlation between the temporal pattern of fluctuation in urethral temperature and that of prostate temperature (r = 0.83; p < 0.001) during treatment.

CONCLUSIONS

Treatment with the microwave thermoablation system fulfilled the requirements for an effective and safe microwave-based BPH treatment modality by exposing obstructive tissue to high temperatures without endangering vulnerable adjacent tissues.

Adenocarcinoma of the prostate: innovations in management

Adenocarcinoma of the prostate (CaP) in the Western world has become the most common noncutaneous human tumor. CaP is also the second most important cause of cancer deaths among the male population in the United States. Major progress was made in the past decade in better understanding this disease process, as well as in improved diagnostic accuracy. This improved diagnostic accuracy was due to wide application of prostate-specific antigen (PSA), use of transrectal ultrasound (TRUS), and greater awareness among clinicians of CaP. The use of PSA in clinical practice has resulted in a sharp increase in the number of patients diagnosed with capsule-confined tumors. The optimal treatment for capsule-confined CaP is in the process of being defined. Radical prostatectomy in the United States is currently the most commonly applied treatment for younger patients. Excellent treatment results with a 10-year actuarial survival > 80% are readily obtainable in properly selected patients. Nerve-sparing procedures helped reduce the high incidence of impotence that occurs in patients after radical retropubic prostatectomy. Radiotherapy remains the other curative treatment method in the management of CaP patients, with long-term survival rates similar to those reported in surgical series. Due to the problem of frequent preoperative tumor understaging, a routine use of postoperative irradiation to the prostatic fossa produces an excellent (> 95%) incidence of local tumor control. Management of patients with metastatic disease has undergone a considerable evolution with the development of modern hormonal management and treatment with strontium-89 to control intractable bone pain. Newer treatment methods such as hyperthermia are currently being investigated. Major efforts are directed toward the reduction of short- and long-term treatment toxicity associated with surgery, radiotherapy, and hormonal management, thus improving patient quality of life.

Temperature-correlated histopathologic changes following microwave thermoablation of obstructive tissue in patients with benign prostatic hyperplasia

OBJECTIVES

To determine the intraprostatic pathologic changes following accurately measured doses of transurethral microwave thermal energy in patients with benign prostatic hyperplasia.

METHODS

Eight patients scheduled for prostate surgery were treated for approximately 1 hour without anesthesia using a newly designed microwave treatment catheter that allows a close impedance match to prostate tissue and concentrates thermal energy preferentially in the anterior and lateral prostate gland. Interstitial, urethral, and rectal temperatures were continuously measured using a novel stereotactic thermal mapping technique. Serial sections of prostate tissue harvested during subsequent surgery were evaluated pathologically with prostate mapping.

RESULTS

Microwave treatment resulted in marked and continuous intraprostate temperature elevation, while urethral and rectal temperatures remained low. Peak intraprostate temperatures in individual patients reached as high as 80 degrees C. Mean temperature reached a maximum of 54 degrees C at a radial distance of approximately 0.5 cm from the urethra and remained 45 degrees C or higher up to a distance of 1.6 cm. The predominant pathologic findings were uniform hemorrhagic necrosis and tissue devitalization without significant inflammation. The mean distance from the urethra to the viable-necrotic tissue border was 1.6 +/- 0.2 cm (range, 0.5 to 2.5). At this border, no more than 1 mm in thickness, temperature averaged 45.7 +/- 0.6 degrees C, and there was a suggestion that pure stromal nodules were more resistant to thermal injury.

CONCLUSIONS

Microwave treatment can destroy obstructive prostate tissue while maintaining innocuous urethral and rectal temperatures. Temperatures of 45 degrees C or higher for approximately 1 hour cause uniform thermoablation of prostate tissue.

An accurate technique for detailed prostatic interstitial temperature-mapping in patients receiving microwave thermal treatment

A minimally invasive prostatic interstitial temperature-mapping technique is described that supplies accurate, detailed information on thermal doses delivered to precisely localized tissue sites. The technique employs a comparatively large numbers of thermosensors, highly accurate placement of those thermosensors at specified three-dimensional coordinates, fiberoptic technology that avoids significant interaction between the thermosensors and the applied microwave field, and continuous temperature readout. Biplane ultrasound imaging and fluoroscopy were used to ensure stereotactic accuracy of thermosensor placement. The technique was applied in 15 patients with benign prostatic hyperplasia (BPH) undergoing a 1-hour microwave thermal treatment session. The thermal mapping procedures and microwave treatment were generally well tolerated. The mean maximum temperature in the prostate and periprostatic tissue (57.9 +/- 1.9 degrees C) was significantly higher (P < 0.001) by more than 18 degrees C than that in either the urethra (39.6 +/- 0.9 degrees C) or the rectum (40.8 +/- 1.7 degrees C). In a representative patient, microwave treatment resulted in stable elevation of temperature 5 mm radially from the urethra that averaged 66.0 +/- 0.1 degrees C. At 10 mm from the urethra, the temperature averaged 50.5 +/- 0.1 degrees C. Urethral and rectal temperatures remained at innocuous levels. In conjunction with pathologic studies, this interstitial thermal mapping method should prove useful in defining the optimal thermal doses for microwave therapy. The method should also find uses in evaluating different microwave treatment systems, which can vary markedly in thermal performance, as well as other modalities that apply heat to prostatic tissue.

Cooled microwave transrectal applicator with adjustable directional beam for prostate treatment

A new intracavitary applicator design for microwave hyperthermia, particularly for transrectal prostate treatment, is presented. It includes an exchangeable multisection antenna that enables us to create a required longitudinal heating pattern, a cooling system to shift the maximum temperature away from the surface and a microwave reflecting system embedded in the cooling system that allows one to shape the irradiation beam in a transverse direction. Independent control of the longitudinal and transverse irradiation patterns of the applicator along with the cooling system, enable precise heating of selected tissues. Results of SAR measurements, E-field measurements and steady state temperature distributions, in solid and liquid tissue-equivalent phantoms are presented. Clinical performance of this applicator was evaluated earlier in patients heated intraoperatively and in a phase I clinical study. The applicator was found capable of effectively heating a tissue volume extending radially 3-25 mm from the applicator surface, angularly defined by configuration of reflecting system and longitudinally determined by specific choice of the multisection antenna.